Improved extendable ladder system

Abstract

A ladder extension system comprises a plurality of pulleys to help reduce the drawing force needed to extend the ladder. The system also comprises an auto-arrest device AAD 30 to help secure the rop

Description

Background There are several professions in which an individual will require the use of a ladder to reach the necessary height to carry out their work. In some cases, the task may require the use of a multi-section ladder in order to have sufficient length to reach the height needed, for example, builders, painters or firefighters that need to reach the top of a building’s exterior. In use, such multi-section ladders comprise a series of overlapping layers, each comprising a ladder with multiple rungs. When needed, the user can slide the inner layers of the ladder upwards, locking the layer in place using Ladder Pawls to extend the length of the ladder to reach greater heights. In some cases, the fully extended ladder may be several stores tall and therefore it will be impractical for a user to try to extend the ladder fully on their own. To this end, ladders may incorporate an extending ladder system configured to allow the user to extend a larger ladder easily. Typically, such a system comprises a rope or cord that the user can pull to actuate the system and extend the ladder to the required length. The problem with such systems is that for larger ladders the amount of force required to actuate the system may be too high for the user. More specifically, as the length and weight of the ladder increase the amount of drive force needed to actuate the extending ladder system is increased. This effect may also result in the user extending the ladder more slowly. This can be a problem in some applications of the system especially fire-fighting wherein the user will be required to deploy the ladder as quickly as possible. Therefore, there is a need to provide an improved ladder-extending system that can reduce the amount of drive force needed to extend the ladder and thereby reduce the time needed to extend the ladder. Further, the system should be designed to reduce the risk of the rope, or cord of the ladder becoming tangled or separating from the system so that the ladder can be deployed quickly with minimal risk of failure. It is also desirable for the claimed system to be configured to be retrofitted such that the improved system can be incorporated into existing ladders and replace the older systems. Summary The present invention provides an improved extending ladder system configured to allow a multi-layer ladder to be extended by applying dive force to a rope, or chord, attached to the system. Wherein the claimed system allows the ladder to be extended with less force than the current systems. This improved system will also comprise a kit of parts, that will allow the user to replace the pre-existing systems already used on other ladders. A multi-section ladder may also be termed a multi-section or multi-tier ladder and is a ladder having a plurality of ladder sections where sections additional to a base section can be extended and secured in an extended position to extend the usable length of the ladder for climbing. The currently used system comprises a pair of pulleys positioned at opposite ends of the ladder, with a rope, or cord coupled to a lower rung of a ladder section or ladder tier that passes through the pulleys. These parts are configured such that, when the rope is pulled the rope rotates over the pulleys and draws the two pulleys together, in doing so the section of the ladder is extended as the lower pulley is pulled upwards by the pulled rope, thus extending the ladder. For safety, one of the pulleys would comprise an Auto-arrest device (AAD) configured to stop the rope from moving and prevent the ladder from collapsing. More specifically, the AAD comprises a spring-loaded member wherein when the rope is under tension, for example, while the rope is being driven, the spring is extended allowing the rope to move through the AAD. The force on the rope pulls the pulley wheel away from a stop. However, should the user release the rope, the rope passing through the AAD is no longer under tension, this releases the spring pushing the stop member, such as a toothed member, into the rope to hold it in place. This will prevent the ladder from collapsing when the rope is dropped. Instead, the user must feed the rope back through the AAD slowly, so that the rope tension keeps the spring compressed as the rope moves through the AAD when collapsing the ladder. As previously noted, one of the problems such systems face, especially when used by firefighters, is the need for the ladder to be deployed quickly. To address this problem, it is preferable to reduce the amount of draw i.e. pulling force that must be applied to the rope or cord to actuate the pulleys and extend the ladder. Several changes have been made to the pulley systems currently used in such ladders to achieve this effect. The first change made to the improved system is that the system comprises an additional pulley such as to provide a pulley block such that the system comprises a pair of pulleys, such as together in a pulley block as part of in addition to the AAD. This additional pulley reduces the force that will need to be applied to extend the ladder. It is noted that the two pulleys used would have different designs as one pulley requires only a single wheel while the other will require a pair of wheels as the rope, or chord, will pass through the double pulley twice as the rope will loop twice through the system, referencing the loop made as the rope extends from the top of the system to the bottom of the system. This layout helps reduce the draw force required when actuating the pulleys. Additionally, the separate loops help to reduce the risk of the rope, or chord, becoming stuck as it moves through the components of the system. On the ladder, the components will be arranged such that the single wheel pulley and AAD are parallel at the top end of the ladder and the double pulley is positioned proximate to the bottom of the ladder, when the ladder is collapsed (not extended), on the layer of the ladder to be extended, such as on a rung of the ladder. In the preferred embodiment of the claimed system, the rope will follow the following path through the system. Starting at the top of the ladder, the end of the rope or chord will be attached to a rung of the ladder using a suitable stirrup that will be riveted into place to secure it to the ladder. The loose end of the rope will then pass through the frame of the single-wheel pulley to help keep the line straight as it moves down the ladder towards the second pulley this can help prevent the rope from becoming tangled with the second loop of the rope. It is noted that this aperture in the pulley frame is preferably an oval-shaped aperture with extends along the length of the ladder, so as to restrict the sideward motion of the rope without restricting vertical motion. Additionally, the round edges of the aperture will reduce the risk of the rope being caught or cut by the edges of the aperture as it moves through the frame. Here the rope makes its first loop passing through the first wheel of the two-wheel pulley. It is noted that the wheels of the two-wheel pulley will be placed vertically adjacent to each other, in this case, the first wheel refers to the wheel that is positioned closer to the top of the ladder. It is noted that it is preferable for the first wheel to have a smaller size compared to the second wheel such that the first loop, created when the rope passes over the first wheel can fit within the second loop created when the same rope passes over the second wheel. This reduces the volume occupied by the rope helping to reduce the size of the overall system while also reducing the risk of the loops becoming tangled as the rope passes through the system. The rope will then extend up the ladder to loop around the wheel of the single pulley completing the first loop, then the rope extends down the ladder a second time to be looped around the second wheel of the two-wheel pulley. Then the rope extends up the ladder again to be passed through the wheel of the AAD. After which the rope extends down the ladder to the user allowing them to pull the rope to actuate the system. These loops reduce the force required to actuate the pulleys and move the ladder. Additionally, the two loops as described above help to ensure that the rope remains under tension regardless of the position of the ladder, this ensures that the rope does not go slack and become tangled as the ladder is extending or receding. It is noted that the wheels of the pulley are all aligned such that the flat sides of the wheel rest against the rungs of the ladder, this ensures that the rope remains in a plane parallel to the plane of the ladder as it moves through the system. This arrangement helps to prevent the rope from becoming entangled with the rungs of the ladder as it moves through the system. It also allows the pulleys to be placed flat against the ladder reducing the volume of the system and allowing the system to be more compact, so that the component of the system can be housed between layers of the ladder without hindering the movements of the same ladder sections. It is noted that the wheel of the AAD is perpendicular to the other wheels in the system as this wheel needs to eject the rope to the user allowing them to pull the rope away from the ladder to actuate the pulleys. It is noted that another change to the system to assist in reducing the driving force is to change the materials used in the system. For example, the frames of the pulley and AAD may be formed from a light metal such as aluminium, while components of the pulley such as the wheels may be formed from a plastic such as nylon. In both cases, these materials are lightweight, thereby reducing the weight of the system. As the system has a reduced weight the amount of drive force needed to actuate the system is reduced. It is further noted that in the preferred embodiment, the wheels used in each of the pulleys and the AAD would comprise a U-shaped profile, wherein around the circumference of the wheel, the centre of the wheel will be recessed relative to the outer edges. This recess helps to guide the rope as it passes over the wheel, ensuring that the rope does not slide off the wheel when it is not in tension. It is noted that the insides of this recessed portion may include a grove or track which is configured to increase the friction between the rope and the surface of the wheel, this lowers the risk of the rope becoming detached from the pulley as the system is actuated, and ensured the rope movements will rotate the wheels of the pulley. Another feature of the preferred embodiment of the pulleys is that the wheels of the pulley are fastened into place using a specialised pin. More specifically, each pulley comprises a base frame and front plate or guard, wherein the wheel is positioned between the base and the front plate, wherein each of the base, the wheel and the front plate comprises an aperture allowing the pulley pin to be passed through each of these components when the apertures are aligned. It is noted that the pin comprises a head at one end, wherein the head has a radius wider than the body of the pin such that the head of the pin will rest on the pulley to hold the pin in place. The other end of the pulley pin comprises an aperture that passes through the body of the pin, such that once the pin is inserted into the pulley the user can pass a suitable fastener or member, such as a fastening pin, through the aperture in the pulley pin to secure the second end of the pin in place, the fastener and the pin head both prevent the pin from moving and falling out of the pulley once it has been inserted. It is noted that these pulleys may be made from the same material as the pulley wheel to help reduce the weight of the pulley. Preferably, the pulley pins are stainless steel this reduces any galvanic effects on the pulley or the body and is wear-resistant. Preferably, wheels are nylon, this reduces friction both on the pulley pin and on the rope. Preferably, the body of the pulley or pulley block is aluminium so as to reduce weight and eliminate any galvanic effects with the ladder which is normally / preferably aluminium. A pulley block refers to a structure wherein a plurality of pulley wheels is assembled alongside one another in a common body. It is also noted that the pulley pins would preferably comprise a gripping feature on the bottom surface of the pin head, in this case, the bottom surface refers to the surface of the pin head that faces and contacts the pulley. The purpose of this gripping feature is to increase the friction between the pin and the pulley to prevent the pin from rotating as the wheel of the pulley rotates. This prevents kinetic energy from being lost from the rope due to the pin being rotated. In the preferred embodiment, the bottom surface of the pin head may comprise a boss, with a none circular shape, and then the first aperture that the pin passes through when inserted into the pulley is configured to have the same shape as the boss on the pin head, this way once the boss is inserted into the aperture it will prevent the pin from rotating when the wheel rotates this reduces friction and wear, particularly when metal-to-metal contact such as body-to-pin rotation is avoided. Further, the pulley pin pressure is therefore reduced by having a larger contained surface. It is also noted that this not only reduces the amount of kinetic energy that is transferred from the pulley wheel to the pin but also reduces the risk of the pin becoming loose or worn as the wheel rotates as the pin is locked firmly in place. In addition to the features described above the claimed pulleys may also include guiding walls configured to guide the rope as it passes through the pulley. These walls help to prevent the rope from disengaging the pulley wheels even when the rope is not under tension. The consequence of the wall shape curvature also reduces contact friction with the rope and hence reduces rope wear. These walls also help to protect the rope from external forces that may damage or wear the rope. To this end, the walls are preferably made of aluminium, which to the extent that it may come into contact with a rope is less abrasive than steel to have sufficient strength to support and protect the rope. However, it is noted that the walls may comprise a combination of steel and aluminium to help reduce their overall weight. The AAD comprises a pulley wheel and a frame similar to the pulleys described above, with the exception that the wheel in the AAD will be positioned so that the plane of the wheel is perpendicular to the plane of the ladder. This orientation of the wheel allows the loose end of the rope to be ejected away from the ladder so that the user can pull on the rope to extend the ladder. The AAD further comprises a frame that will be mounted to the ladder rung, which includes a face plate that covers the centre of the wheel so as to protect the wheel from outside forces, and may also act as a guiding wall helping to prevent the rope from detaching from the wheel of the AAD. Additionally, the AAD comprises a spring-loaded member positioned adjacent to the wheel, such that the end of the rope that passes through the AAD is positioned between the wheel and the member, this member will be configured such that when the rope is slack, meaning not under tension, the spring snaps the AAD closed, thereby trapping the rope with the member and preventing the rope from moving. This prevents the pulleys of the system from being actuated thereby holding the ladder in its current position. This can prevent the ladder from retracting, for example, when the user releases the rope. This prevents unintentional retractions of the ladder. This in turn prevents the ladder from falling once deployed which lowers the risk of harm to individuals on the ladder, as they will not become trapped between the collapsing section of the ladder and there is a lower risk of the ladder falling down. As mentioned above, the AAD acts to snap closed upon release of the rope, thus increasing the safety margin and the potential for the rope to move through the pulleys and the ladder to collapse. Even a relatively short movement may be important as upon a ladder retracting in a section ladder the rungs pass past one another and effectively have a shearing / scissor action which can be a safety issue, particularly given the weight of ladders, several hundred kilograms of ladders used, for example in fire safety. A preferred use of the present invention is with, in or as part of rescue ladders for fire services which are inherently very substantial. In respect of the snap action the use of the aluminium body and the nylon pulley is particularly advantageous as this reduces the mass of the pulley for any given pulley size and hence reduces the inertia of the AAD and hence its rate of closure is improved. Then when the user pulls on the end of the rope, putting the rope under tension, the rope forces the member open, extending the spring in the AAD, thereby allowing the rope to move through the pulley system allowing the ladder to extend. When retracting the ladder, the user will need to keep the rope under tension, feeding the rope slowly back into the AAD. This ensures the ladder can still be deployed quickly but will only retract when the user intentionally feeds the rope into the system under the tension making the retraction of the ladder more controlled. In the claimed system the AAD may further comprise a sheath positioned around the spring in the AAD. The purpose of this sheath is to keep the elongated axis of the spring in line with the member and thereby prevent any non-axial movements of the spring. More specifically the sheath allows the spring to compress and expand along the longitudinal axis but does not allow the spring to move or bend laterally. This configuration ensures that the spring does not lose kinetic energy through these lateral movements. This in turn helps to reduce the amount of force needed to compress the spring. As a result, the amount of draw force needed to open the AAD can be reduced. Lastly, it is noted that the type of rope, or chord, used for the system is preferably designed to reduce the amount of draw force needed to actuate the system. This means that the material for the rope is preferably lightweight. It is also noted that if the ladder is being used by firefighters there are other considerations, such as a need to ensure the rope does not absorb water, that will likely drip down from a fire hose, as this can result in the weight of the rope increasing and may also increase the diameter of the rope. Both of these make it more difficult for the user to pull the rope through the pulley system. To this end, the rope is preferably a plastic, more preferably a nylon or polyester rope., as this is a relatively lightweight and waterproof material. It is noted that the commonly used rope comprises or consists of nylon which the rope is nylon 11, as the material is lightweight and waterproof, and is sufficiently impact resistant such that the material will not warp or tear after repeated uses. However, in the preferred embodiment, a more preferable material may be where the rope comprises, predominantly comprises or consists of nylon 6. Nylon 6 may be preferable as it has a higher heat resistance compared to nylon 11, this can be especially useful when the rope is being used by firefighters. Additionally, nylon 6 rope has a lower elasticity, this helps to reduce the required drive force needed to actuate the pully as the rope will expand less before becoming under tension thereby wasting less energy when the rope is being pulled. As previously mentioned, a beneficial feature is the snap action of the AAD. However, the effect of this is that the rope is stopped more abruptly and as such elasticity of the rope is of greater importance. The use of nylon 6 is therefore particularly preferable in the present invention due to the rapid closure of the AAD and the need to reduce the elastic extension of the rope and hence the aforementioned scissoring action, which will be even more deleterious if it effectively is repeated in a yo-yo type repetition due to rope elasticity. In embodiments wherein both the rope and the pulley wheels are made from plastic, there may be a risk of static charge building in the plastic rope. However, in most embodiments, the ladder the rope is attached to is made of metal, therefore the rope may be grounded through the ladder. In all cases, the anchored end of the rope is attached to said ladder via the stirrup and rivets described above and therefore should always be able to discharge safely through the ladder before the charge builds to dangerous levels. The claimed invention may further comprise a kit of parts that may be used to provide a ladder with the claimed expansion system, or a system that may be retrofitted onto ladders that are also being used. To this end the simplest form of the kit would comprise the pulleys and AAD as described above that can be retrofitted onto existing ladders using the ropes that are used in the current system. The kit may then include additional parts, such as the rope as described above and a suitable stirrup and rivets to anchor the rope to the ladder, and may include a suitable ladder that can utilise the extension system. The kit of parts may include suitable tools for fastening the fasteners used to couple the parts of the system together, including a rivet gun for the stirrup rivets. The tool and the fasteners are optically valuable components for the kit as otherwise it has been found that users may improvise with their equipment and the specific tolerances and application force used further desirable may not be applied, the fasteners are important to the safety and efficiency of the product. By using a system as described above the user is able to utilise a multilayer extending ladder that can be deployed quickly with little risk of the ladder collapsing when in use. The extension system of the present invention also incorporates features designed to reduce the amount of pulling / draw force necessary to extend the ladder manually, allowing the ladder to be deployed more safely, efficiently and even potentially faster, and allowing the extension system to be used by a wider range of ladders. Detailed Description The claimed invention is illustrated in the following figures: Figure 1 - depicts the parts of the single-wheel pulley Figure 2 - depicts the parts of the double-wheel pulley Figure 3 - depict an example auto-arrest device (AAD) with a spring sheath Figure 4 - depicts the parts needed to form the example AAD of Figure 3 Figure 5 - depicts an example of the claimed system attached to a ladder, with views from the front and rear of the ladder Figure 6 - depicts a ladder utilising the claimed system Figure 7 - depicts an example single-wheel pulley and double-wheel pulley with anti-pooling features Figure 7A - depicts a variant of the double wheel pulley of Figure 7 Figure 7B - depicts a variant of the single-wheel pulley of Figure 7 The claimed invention as depicted in the figures comprises the following parts, note that like reference numerals are used to indicate like parts through the figures. 10 - Single wheel pulley 11- Pulley base 12 - Pulley wheel 13 - Faceplate / guard 14 - Oval aperture 15 - Pulley pin 16 - Fastener pin 17 - Fastener 20 - Double wheel pulley 21 - Pulley base 22 - Primary pulley wheel (large) 23 - Secondary pulley wheel (small) 24 - Faceplate / guard 25, 25’ - Pulley pin 26, 26’ - Fastener pin 27 - Side guards 30 - Auto-arrest device (AAD) 31 - Base frame 32 - Faceplate 33 - Arresting member 34 - Spring 35 - Mounting frame 36 - Pully wheel 37 - Spring sheath 40 - Ladder 41 - Ladder support legs 42 - Ladder rung 43 - Ladder inner section 44 - Ladder outer section 46 - Ladder base support 50 - Rope 51 - Stirrup 60 - Base anti-pooling aperture 61 - Wheel anti-pooling aperture 62 - Flat surface pulley wheel The claimed invention provides an improved system for extending multi-tier ladders. In particular, the present invention provides an enhanced extension line system for multi-tier ladders, specifically designed to improve safety and ease of use in fire services. This is achieved by providing a system that reduces the driving force that needs to be applied to the ladder to expand and retract the different tiers. The claimed system comprises at least a pair of pulleys and an auto-arrest device (AAD) with a suitable rope, or chord passed through each of these components with one end of the rope secured to a section of the ladder via a stirrup. Wherein the components are arranged on the ladders such that when a user applies a driving force to the loose end of the rope, the pulleys are actuated and the tiers of the ladder extend. Figure 1 depicts the first type of pulley used in the claimed system specifically a single-wheel pulley 10. The pulley comprises a base frame 11, which provides a support structure that can be mounted to a rung of the ladder and to which the other components of the pulley can be mounted to. This base is preferably shaped to be substantially planar, or flat, so as to reduce the volume of the overall pulley and to ensure that the bulk of the pulley does not obstruct the movement of the various ladder tiers. This base is preferably formed from metal to ensure that the base is sufficiently strong to support the various components mounted to it and ensures that the frame can withstand potential impacts for example if the ladder falls over. In the current system, such bases are typically made from 304 stainless steel to ensure they are weather-resistant and sufficiently strong, however, these frames can be quite heavy. Therefore, the claimed invention would preferably use an alternative metal or alloy which would have less weight while still being suitably weather resistant, especially resistant to water as the ladder is likely to be used outdoors where it could rain, but also because the hose used by the firefighter in the ladder may also spill water onto the system. To this end the frame may be formed from suitably strong aluminium, such as 5251 aluminium, which has a reduced mass compared to the steel frame, however, it is also weaker, meaning it is more likely to bend and deform when impacted or under stress. Therefore, the preferred embodiment of the pulley frame would comprise a combination of stainless steel and a lighter metal, such as a combination of 5251 aluminium and 304 stainless steel, wherein the sections made from aluminium reduce the overall mass of the pulley and the inclusion of steel sections ensures the overall structure has high durability. It is also noted that the base 11 comprises a plurality of apertures configured to receive fasteners such as bolts, or pins, to fasten the base 11 onto a suitable ladder and also to fasten the different components on the pulley 10 onto the base 11. It is noted that the base frame 11 may comprise an additional aperture configured to allow water to pass through the surface of the base 11. These apertures prevent water from pooling on the pulley, as such pooling may cause additional wear to the components of the pulley. Lastly, the frame comprises a large aperture configured to allow the rope used in the system to pass through the frame. In this case, the base 11 comprises an oval aperture 14. This aperture is necessary as the claimed system uses multiple pulleys, creating separate loops of rope, therefore the aperture allows the rope to pass through the pulley on a first pass to form the inner loop before going over the wheel of the pulley when forming the second outer loop. This rope aperture preferably comprises a round shape such as an oval or circle to ensure there are no sharp corners that may cut or otherwise damage the surface of the rope as it passes over the edge of the aperture 14. It is noted that the oval shape is more preferable as it will allow the rope to have more freedom to move along the elongate axis of the aperture. This additional freedom will allow the rope to move vertically as well as allow the rope to more easily move out of the plane of the base 11, without putting the rope under additional stress. This will allow the user to align the rope with other components of the system more easily. The first component that is mounted to the base 11 is the pulley wheel 12. It is noted that this pulley 10 only requires a single wheel 12. The wheel 12 that is coupled to the pulley 10 will preferably be made from a lightweight material, such as a plastic or polymer, like nylon, to reduce the overall weight of the pulley. However, it is noted that such wheels may be more vulnerable to impacts. Therefore, in some cases the wheel 12 may be made of metal similar to the base 11, however it is noted that such metal wheels will require bearings housed near the rotational axis of the wheel to reduce the wear of the axis the metal wheel will rotate around, this may include ball bearing or roller bearings. However, it is noted that the inclusion of any type of bearing may further increase the mass of the wheel with the inertial effects mentioned above. As such the plastic wheel is preferable, especially as the base 11 is configured to support and at least partially protect the wheel 12, meaning the relative weakness of the material is less of a hindrance compared to the heavier weight of the metal wheel. It is noted that the lighter weight of the plastic wheel may also reduce the amount of force needed to rotate the wheel 12, this allows the pulley to be actuated with less drive force on the rope. Regardless of the material chosen, it is preferable that the wheel 12 have a U-shaped profile along its circumference. This refers to a profile wherein, along the circumference or edge of the wheel 12, the centre of the edge is receded compared to the outer edges, creating an indentation along the wheel’s circumference with sufficient volume to house the rope that is passed over the wheel 12. This trench along the edge of the wheel 12, prevents the rope from moving laterally as the wheel rotates, as the raised edges of the profile will prevent the rope from sliding. This reduces the risk of the rope becoming detached from the wheel 12 when the wheel is rotating or when the rope is not under tension. It is also noted that when the rope is under tension the lack of lateral moment can help ensure that more energy is transferred from the rope to the wheel 12 in the radial direction, this ensures that the rope turns the wheel 12 more efficiently meaning the wheel can be rotated with less driving force applied to the rope. However, one problem with using the plastic wheel, is that the relatively smooth surface of the wheel 12 will reduce the amount of friction between the wheel 12 and the rope attached to the pulley 10. This lack of friction may reduce the amount of energy that is transferred between the pulled rope and the wheel 12. Therefore, it may be preferable for the system to include features that are configured to increase the friction between the wheel 12 and the rope. Specifically, the surface of the U-shaped profile in the wheel 12 may include friction features, such as a trench or groove, or features similar to the tread on a tyre. Wherein the feature is configured to increase the friction between the surface of the wheel 12 and the surface of the rope to ensure that the energy from the pulled rope is transferred to the wheel to actuate the pulley 10. This ensures that the pulley 10 assists in the movement of the rope thereby reducing the pull force that needs to be applied to extend the ladder. Another component that is coupled to the base 11 is the front plate 13, sometimes referred to as a front guard as the purpose of the plate 13 is to partially cover the surface of the wheel 12 so as to protect the wheel from impact, while still allowing space for the rope to be wrapped around the wheel 12. To this end, the plate 13 comprises a piece of metal that is configured to be attached to the base 11, via fastener apertures proximate to one or both ends of the front plate 13, such as the depicted fastener 17. The plate will further comprise a raised portion between the ends that is configured to be positioned over the wheel 12, such that the body of the plate covers the top surface of the wheel, noted that in this case, the top surface refers to the surface of the wheel 12 facing away from the base 11. This way the plate 13 can intercept any impacts that would hit the top surface of the wheel 12, thereby protecting the wheel. As previously noted, the plate 13 will be made from metal, and as with the base, there needs to be a compromise between reducing the pulley’s weight and providing improved durability. Therefore, the plate 13 may be made from aluminium, or a combination of aluminium and steel as described for the base 11, as this would reduce the overall weight of the pulley. However, given the relatively small size of the plate 13 and the fact that the purpose of this plate is to provide protection, it may be preferable that the plate 13 be made from aluminium to minimise weight, as this would have less effect on the weight of the pulley 10 compared to using a base made entirely of stainless steel. It is noted that the raised portion of the front plate 13 also comprises an aperture. This aperture is configured to align with the aperture in the centre of the wheel 12, and a corresponding aperture within the base 11. These apertures when aligned are configured to receive a fastener or member that will act as the axis which the wheel 12 will rotate around. The ends of this fastener or member will be configured to hold the fastener or member in place without impeding the rotation of the wheel 12. In the depicted example the axis fastener is in the form of a pulley pin 15. This pulley pin is configured to have a head that is wider than the body of the pin, such that when the pin 15 is passed through the aligned apertures as described above the head of the pin will rest on the surface of the base 11 or front plate 13 thereby stopping the pin from passing through the pulley 10. The end of the pin body remote from the pin head comprises a small aperture that passes through the body of the pin in a direction perpendicular to the pin body’s elongated axis. These apertures are configured to receive a further fastener or member such as the depicted fastener pin 16. This further fastener is configured to prevent the pulley pin 15 from being removed once inserted, thereby securing the pulley pin 15 in place within the pulley 10. As noted, the pin will act as the rotational axis for the wheel 12, therefore it is preferable to have the pulley pin 15 be made from stainless steel and the pulley from nylon as previously mentioned as the wheel 12, as this ensures that neither the pin 15 nor wheel 12 providing an optimal combination of resistance to wear and reduced mass. However as noted earlier, there may be concerns regarding the relative weakness of the plastic used for both the wheel 12 and the pin 15, therefore the user may incorporate bearings as described for the metal wheel to help reduce the force acting on the pin 15. In such cases, it may be preferable to use the roller bearing over one or more ball bearings, to ensure that the weight from the rope and any frictional force from the wheel 12 is dispersed over a wider area to reduce the force acting on the pin 15. Further, it is noted that there can be a problem wherein the pulley pin 15 is free to rotate, thereby the pin may draw kinetic energy out of the wheel 12 when the wheel tries to rotate making it more difficult for the user to rotate the wheel 12. To address this problem, the pulley pin 15 should comprise one or more features configured to prevent the pin 15 from rotating. For example, the bottom surface of the pin head, which refers to the surface of the pin head in contact with the pulley 10 may comprise a gripping feature, such as a protrusion or grooves configured to increase the friction between the surface of the pin head and the surface of the pulley, thereby preventing the pulley pin from rotating as the wheel 12 spins. However, it is noted that with such a feature there is still a possibility of the pin 15 rotating. Therefore, a different method is needed to prevent the pin 15 from rotating. The preferred method of preventing the pin 15 from rotating is depicted in the example pulleys 10,20. This method comprises the use of a boss on the bottom surface of the pin head, wherein said boss has a non-circular polygonal shape, wherein the first aperture of the aligned apertures that receives the pulley pin 15 which has a shape that matches the shape of the boss. This can be seen in the depicted example by the square aperture in the face plate 13. With this configuration, the boss on the pin head will be inserted into the first aperture, once inserted the pin 15 will no longer be able to turn as the boss will not be able to turn within the first aperture. This provides an improved method of ensuring that the pin 15 does not rotate as the wheel 12 rotates. In doing so the transfer of energy between the wheel 12 and the rope will be more efficient. Figure 2 provides an example of the other type of pulley used in the claimed system, specifically the diagram shows the parts of a double-wheel pulley 20. As previously noted, the claimed system uses additional pulleys to reduce the driving force needed on the rope to extend the multi-tiered ladder. As part of this, the claimed system forms multiple loops with the rope of the system to better disperse for force applied to the system allowing the ladder to be extended more easily, to accommodate these multiple loops the system requires at least one double wheel pulley 20 wherein each loop of the rope will pass over a different wheel. To this end, the pulley requires two wheels with sufficient space for the rope to pass over each wheel. It is noted that in the preferred embodiment, these wheels will be positioned adjacent to one another, being separated vertically in the direction of the ladder’s longitudinal axis. This arrangement helps to keep the width of the double wheel pulley to a minimum and also helps to reduce the width of the overall system as this arrangement for the wheels 22,23 allows the rope loops to be positioned one inside the other meaning less space is needed for the rope loops. It is also noted that the wheels of the double wheel pulley 20 should be co-planar, that is to say, the adjacent wheels 22,23 should be parallel and positioned to be in the same plane to further reduce the volume of the pulley. By taking these measures to reduce the size of the pulley 20, the user can minimise the weight of the system and ensure that the parts of the system can be coupled to a wider range of ladders due to their smaller more compact design. It is noted that the double-wheel pulley 20 comprises similar components to the single-wheel pulley 10, in which the double-wheel pulley comprises a base 21, wheels 22,23 and a front plate 24 similar to the ones described above for the single-wheel pulley 10. Additionally, these components are held together with fasteners and pulley pins 25,25’ as described above. It is noted that these components would be made from the same materials as the corresponding component of the single wheel pulley 10 as outlined above to reduce mass while maintaining sufficient strength and durability. However, there are some key differences in the design of the double-wheel pulley 20 when compared to the single-wheel pulley 10. Firstly, the double wheel pulley 20 includes an additional wheel 23 in place of the oval aperture 14. However, is noted that both wheels 22,23 are still coupled between a base plate 21 and front guarding plate 24, and each is held in place using a respective pulley pin 25, 25’ just like the wheel in the single wheel pulley 10, with the front plate 24 comprising a raised portion long enough to cover the surface of both wheels, while ensuring there is enough space to loop the rope radial around each of the wheels 22,23. Further, each of the wheels 22,23 is preferably made from plastic, like nylon, and will preferably comprise a II-shaped profile around their circumference as described for wheel 12 of the single wheel pulley 10. The difference is that the double wheel pulley 20 may require wheels of different sizes, namely a larger primary wheel 22 and a smaller secondary wheel 23. It is noted that the primary wheel 22 may be the same size as the wheel 12 used in the single wheel pulley 10, or maybe smaller to make it easier to fit two wheels on a single base 21. In any case, the secondary wheel 23 is significantly smaller than the primary wheel 22. This is so the rope loop formed around the secondary wheel 23 can more easily fit within the loop formed around the primary wheel 22. It is noted that the width of these loops when the rope is under tension will be determined by the width of the respective wheel the loop is formed around. To this end, the innermost wheel, relative to the centre of the ladder should be smaller than the outer wheel. In some cases, the wheels 22,23 may be sized in a 2:1 ratio however, such a large size difference may result in the secondary wheel 23 being too small to support the weight applied by the rope, thereby increasing the risk of the secondary wheel 23 breaking under stress when the rope is under tension, and may have too small a surface to have good traction with said rope when the wheel 23 turns, thereby increasing the risk of the rope sliding across the wheel 23 without turning it. As such it is preferable for the primary and secondary wheels 22,23 to have a small difference in their size ratio. A preferred ratio would have the wheels sizes be 95:60 this means the wheels 22,23 are closer in size while still providing enough difference in the width of the loops of rope that they form for the loops of rope to fit inside one another, without the sides of the loops rubbing together, as this may cause additional wear to the rope when the system is actuated. However, it is noted that depending on the thickness of the rope to be used the ratio of the wheels 22,23 may be adjusted to provide larger or smaller loops of rope as necessary. Another difference between the single-wheel pulley 10 and the double-wheel pulley 20 is the inclusion of one or more side guards 27. These side guards 27 serve two purposes as they protect the rope and wheels 22,23 of the pulley 20 from potential impacts from the side. They also form a guiding channel to help direct the rope as it passes over the wheels of the pulley. More specifically, the side guard 27 can act as a barrier between the outer loop of rope formed over the primary wheel 22, and the inner loop of rope formed over the secondary wheel 23. The side guards 27 may also be positioned to prevent the rope from decoupling from the wheels 22,23 by limiting the space radially around one or both of the wheels 22,23. As with the face plate 24, the side guard 27 will preferably be made from a durable material to absorb the force of impacts on the pulley 20. As such the side guards are preferably made of metal, in particular a chemically resistant durable metal like stainless steel. Though as previously noted such a plate may be too heavy, so in some cases the guard 27 may comprise a mixture of metals, or alloys, which combines the durable material, like the aforementioned stainless steel with a more lightweight material like aluminium to reduce the overall mass. In the depicted example, the pulley comprises a pair of side guards 27, these side guards are coupled to the base 21 by a pair of fasteners, such by means of a rivet. The use of rivets in the present invention is preferable as they cannot be shaken loose in normal use. The side guards 27 comprise raised walls that cover the sides of the wheels 22,23. It is noted that the wall of the depicted side guards 27 are in two sections. These sections comprise a broader section which covers the larger primary wheel 22 and a smaller section that covers the side of the secondary wheel 23. It is noted that the broader sections in the depicted example cover a portion of the top and side of the primary wheel 22, this allows the wall to protect the wheel 22 in two directions and ensures that the loop of rope around the wheel 22 does not disengage the wheel 22. It is noted that these walls may include an angled portion towards the end of the wall proximate to the secondary wheel 23 which deflects the wall away from the centre of the pulley 20. This angle portion will help to guide the rope back towards the wheel 22 should the rope move laterally; it also allows the outer loop of the rope to widen as it moves away from the wheel 22. This allows the smaller loop of rope to fit within the larger loop more easily. In the depicted example, the smaller sections of the side guard are positioned to cover the side of the secondary wheel 23 thereby protecting the wheel 23 from impact. Further, it can be seen that the smaller sections of the side guard 27 are narrower than the larger portion, in this case, narrower refers to the wall being closer to the centre of the pulley 20. These narrower wall sections ensure that the wall is close enough to the surface of the secondary wheel 23 to prevent the inner loop of the rope from disengaging from the wheel 23. This narrower wall section also acts as a separator between the two loops of rope that pass through the double loop pulley 20. More specifically, the smaller inner loop will contact the inward-facing surface of the wall, between the small section and the wheel 23, while the larger outer loop contacts the outward-facing surface of the narrow wall section, referring to the side facing away from the wheel 23. This way the narrower wall section acts as a separator ensuring the rope from the loop does not become entangled as they enter or leave the pulley. This can prevent the rope loops from becoming entangled when the rope is not under tension, or when the ladder sections are moving. Figure 3 depicts an example of an auto arrest device (AAD) 30 that is used as part of the claimed system, the depicted example includes a new spring sheath 37 also depicted in the figure. Figure 4 depicts all of the parts needed to form the example AAD 30 depicted in Figure 3. The AAD 30 is a safety device that is used to prevent the multi-tier ladder from collapsing, which in this case refers to the section of the ladder folding back down to its original position before the ladder was extended. The AAD 30 works by having a pulley wheel 36 and locking member 33 positioned such the rope used to extend the ladder passes between the wheel 36 and the member 33. Wherein one of the wheels 36 or member 36 is spring loaded such that the wheel 36 and member 33 are forced together. The member is optionally a cam in the cam may have a toothed service both providing faster action .This results in the rope becoming trapped between the wheel 36 and the member 33, thereby locking the extension system in place as the rope can no longer move through the pulleys 10,20 thereby locking the tiers of the ladder in place. However, this only occurs when the rope is not under tension, for example after the ladder is extended or when the user accidentally releases the rope while operating the ladder. This helps prevent the ladder from collapsing when the ladder is extended or being extended. This lowers the risk of injuries when there are individuals on the ladder as there is less risk of the ladder collapsing and falling under the individuals on the ladder. It may also protect the ladder from being worn or damaged as the user collapses the ladder for storage after use. This is because the AAD 30 has the added effect of limiting the speed at which the ladder can be collapsed. This way the tiers of the ladder can only be lowered slowly to prevent excess wear to the ladder caused by friction between the moving tiers. This will also prevent the ladder from collapsing too quickly wherein the ladder may impact the ground or the lower layers of the ladder possibly damaging the ladder. Therefore, the use of the AAD 30 not only makes the ladder safer to use but may also help increase the operational lifespan of the ladder. To achieve this effect as previously mentioned either the member 33 or the wheel 36 is spring loaded, so that when the spring contracts the member 33 and wheel 36 are forced together trapping the rope between them. However, when the user pulls the rope, bringing the rope under tension, the force exerted by the rope onto the surface of the wheel 36 or the member 33 will cause the spring to extend. This contraction will separate the wheel 36 and member 33 thereby allowing the rope enough space to move through the AAD 30, this will allow the rope to move through the system allowing the ladder to expand or collapse depending on the direction of the rope’s movements. This also means that the rope has to be under tension to allow the ladder to collapse. This means that in use, the user must pull the rope to put it under tension and then feed the rope slowly into the AAD 30 to collapse the ladder. As previously mentioned, Figure 3 depicts a spring sheath 37. This sheath 37 is a piece that can be included in the AAD 30 and is comprised to house the spring used to operate the AAD mechanism as described above. The sheath 37 comprises an opening with sufficient volume to house the spring, with sufficient length to allow the spring to expand and contract in order to operate the AAD 30. However, the opening of the sheath 37 will be shaped so that the spring cannot move laterally, which in this case refers to any direction other than along the elongated axis of the spring, along which the spring expands and contracts. The spring is restricted within its lateral envelope, without the detriment such as by impairment of the physical spring function. This restriction of the spring’s moment ensures that the kinetic energy applied to the spring is not wasted on unnecessary movements, which can reduce the amount of force needed to contract the spring. This sheath can also prevent the spring from becoming detached from the AAD 30 as the restricted movement can prevent the spring from sliding out of the AAD mechanism and can also reduce the risk of the spring becoming tangled when expanding and contracting particularly due to ingress of extraneous material, such as detritus which may be a significant problem particularly in firefighting applications. Additionally, the sheath 37 protects the spring since its sides surround it, protecting it from impact. Figure 4 depicts the parts of the preferred embodiment of the AAD 30 used in the claimed system. In the depicted example it is shown that the AAD30 comprises a base frame 31, which includes a protective face plate 32, an arresting member 33, a spring 34 and pulley wheel 36 coupled to a mounting frame 35, and the spring sheath 27 as described above. The base frame 31 comprises a metal frame that is used to mount the AAD 30 to the ladder and is also used as a base for the other features of the AAD to be mounted. Similar to the base 11,21 of the pulleys, the base of the AAD 30 comprises a frame made from metal. As with the other bases, the metal needs to be chemically resistant and durable to protect the other components of the AAD 30. It is noted that in the case of the pulleys 10,20 the bases 11,21 were formed using a plate onto which the other components are mounted. In contrast, the base frame 31 of the AAD 30 is a hollow frame that houses the components within the space in the centre of the frame. The reason for this is that the section of the rope that passes through the AAD 30 needs to be guided away from the ladder so that the user may pull the rope. As such the wheel 36 and the rope will be positioned perpendicular to the plane of the base and the ladder. Therefore, the base 31 needs to be configured such that the rope and wheel 36 can pass through the base 31, while ensuring the AAD 30 has as flat a profile as possible, by housing all the perpendicular components within the hollow centre of the frame so the user can ensure that the AAD 30 has a small volume. As noted with the pulleys 10,20 the smaller volume and near flat profile ensure that the system does not obstruct the movements of the ladder, and minimises the weight of the system, thereby reducing the force needed to extend the ladder. As with the other bases, the user will use a base frame 31 made from a material that is chosen based on the compromise of reducing weight while also providing durability. Therefore, the user may choose a metal, an alloy or a combination of metals and alloys, such as stainless steel, aluminium or a mixture thereof. It is also noted that the depicted example of the base 31 includes an optional face plate 32 which is configured to extend over the gap in the centre of the base frame 31 in a position that will cover at least a portion of the pulley wheel 36. It should be noted that a similar plate may also be used to protect the other components of the AAD 30 so long as there are sufficient gaps between the plates to allow the rope to pass through the AAD 30. As with the other face plates, plate 32 will be coupled to the base 31 using suitable fasteners, such as a plurality of bolts, and will be made from the same material as the base, or a more durable metal / alloy to provide better durability, such as being made from stainless steel only. It is also noted that in addition to the apertures required to fasten the face plate 32 onto the base 31, the sides of the base frame 31 will comprise further fastener apertures configured to receive the fasteners required to secure the other components to the base frame. These apertures will be positioned along the legs of the frame around the edge of the central gap. The component to be mounted to the frame is the spring sheath 37 as described above this sheath helps to protect and limit the movement of the spring 34 specifically to ensure the spring is working within its lateral &axial envelope. The sheath will be configured to fill at least a portion of the gap within the frame 31 and will comprise a channel wide enough to receive one or more of the AAD mechanism components. In some cases, the sheath 37 will house the spring 34 only, however in the depicted example the sheath can house the spring 34, the arresting member 33 and the mounting frame 35. It is noted that the sheath will comprise apertures that are configured to align with the fastener apertures of the frame 31 to allow the components within the sheath 37 to be fastened to both the sheath 37 and the frame 31. It is noted that the sheath 37 is preferably made from a lightweight material to limit the mass of the AAD 30. It is also noted that though the sheath 37 should be durable it will be protected in part by the base frame 31. Because of this, the preferred material for the sheath 37 is a plastic, such as nylon, similar to the plastics used for the various pulley wheels within the system. The next component of the AAD 30 is the arresting member 33 in the form of a toothed cam. This member is configured to controllably grip the rope within the AAD 30 to prevent the rope from moving. However, the user also needs to be able to open the member when they apply force to the rope. Therefore, the arresting member 33 may be a spring-loaded such that when the rope is under tension the spring contracts, retracting and releasing the member 33. In other cases, the member 33 may be mounted to a rotational axis, like the one shown in Figure 4 allowing the member to freely rotate when it is not forced closed by the spring-loaded mechanism. When this member is freely rotating it will allow the rope to pass through the AAD 30. Note that in the depicted example the rotating member is shaped such that it has a curved surface that will contact the surface of the rope. This curved surface allows the member to be rotated by the movement of the rope should the rope become detached from the pulley wheel 36. This way the AAD 30 may be tripped to trap the rope should it become detached from the wheel 36. This ensures the AAD 30 will stop the rope if the rope travels through the AAD 30 too quickly as described above, even when the spring is contracted, as the rotating member 33 will trap the rope between the curved surface of the member and the surface of the wheel 36. Additionally, the surface of the member 33 that contacts the rope will preferably include gripping features, these features are configured to increase the amount of friction between the member 33 and the surface of the rope. These gripping features may include grooves tread, or protrusions like the ones on the surface of the depicted member 33. The AAD also comprises a pulley wheel 36 like the ones used in the pulleys 10,20 described above. As with the other wheels, the wheel 36 preferably has a U-shaped profile around its circumference to provide a guiding channel that will prevent the rope from sliding off the wheel 36. This channel may also include gripping features such as trenches, groves or protrusions to increase the friction between the rope and the wheel 36. It is also noted that the wheel 36 is preferably formed from a plastic, like nylon for the same reasons as the other wheels used in the system. However, the wheel may also be made of aluminium. It is also noted that the U-shape channel in the wheel 36 will help to guide the rope into the rest of the system, this means that a user may be able to actuate the system even when they are pulling the rope at an angle relative to the ladder as the sides of the wheel 36 will guide the rope and stops the rope from sliding off of the wheel 36. However, unlike the wheels 11,21 of the pulleys 10,20 the wheel 36 of the AAD is not coupled to the base using a pin but is instead mounted to a mounting frame 35, wherein there is a pin that passes through the centre of the wheel 36 and the ends of the mounting frame 35 it is noted that just like the base frame 31, the mounting frame 35 is also hollow to allow the wheel 6 to rotate freely within the frame 35, it is also noted that the hollowed out portion of the mounting frame 35 is wide enough to house both the wheel 36 and the member 36 with enough space for the rope to pass between the wheel 36 and the member 33. It is also noted that the ends of the axis that passes through the wheel 36 will also pass through a slot within the base frame 31. Wherein the ends of the axis can be fastened to the base frame 31 via a suitable fastener such as a pin or nut, that will allow the axis of the wheel to slide up and down the slot thereby allowing the wheel 36 to slide up or down depending on whether the rope is under tension. The top of the mounting frame 35 is coupled to one end of the spring 34 used to control the AAD 30. The other end of the spring 34 is then anchored to the base frame 31 and / or sheath 37, via a pin, member or fastener. In this arrangement when the rope is under tension the force from the rope will push the wheel 36 downwards, as the axis of the wheel slides down the slot in the base frame 31. This will in turn extend the spring 34 via the movement of the mounting frame. When the spring 34 is extended this way the gap between the wheel 36 and member 33 widens allowing the wheel 36 to rotate and allowing the rope to pass through the AAD 30 allowing the system to be actuated. Similarly, when the rope is no longer under tension the spring will contract pulling up the mounting frame 35 a wheel 36, causing the rope to become trapped between the wheel 36 and member 33 thereby locking the system and locking the ladder in its current position. It is noted that due to the use of multiple rope loops and lighter system components, the amount of force needed to actuate the ladder extension system is reduced. Therefore, in such a system the spring 34 used in the claimed system may be weaker than the spring used in a conventional system, this refers to the spring needing less force to be extended. This weaker spring further reduces the amount of force needed to actuate the system. However, it is noted that there is a limit to how weak the spring can be based on UK standards EN 1147:2010 section 7.1 which specifies that the force needed to actuate the ladder extension system can be no more than 500N and no less than 260N. Therefore, the spring requires sufficient strength that when a force under 260N is applied to the rope the AAD 30 will close. It is also noted that the member 33 may be shaped such that if a force of over 500N is applied to the rope the friction on the member 33 will rotate the member closed even when the spring 34 is extended. The reduced spring rate is proportional to the weight of the extending sections and not related to the pull force. (The force acting on the rope extends the spring by the method of constant tension action through the rope, if this tension is interrupted (user removes hands from rope) the AAD spring will compress back to its nominal resting position and the Toothed CAM with rotate and lock the rope against the CAM face and the Pulley, this action can only be operated and used whilst the extended / moving sections are not Pawled (locked onto the adjacent ladder rungs by means of the Ladder Pawl mechanism. Figure 5 depicts the claimed ladder extension system coupled to a ladder 40, showing the view from the front and rear sides of the ladder 40. It is noted that the depicted system shows the state of the system when the ladder is extended as shown by the proximity of the single-wheel pulley 10 and double-wheel pulley 20. In this example, it can be seen how the different components are arranged to be coplanar with each other and with the rungs 42 of the ladder. It is noted that each of the pulleys 10,20 and the AAD are coupled to specific rungs 20 on the ladder using suitable fasteners, such as bolts or rivets, such as M6 bolts, that will pass through the frame of the component and the rung of the ladder. In the depicted example the single wheel pully 10 and AAD 30 are mounted between the 19th and 18th rung near the top of the ladder on a lower tier of the ladder 40, thereby anchoring the position of these components as the section of ladder they are mounted to will remain stationary. While the double wheel pulley 20 is mounted between the 2nd and 3rd rung on a higher tier of the ladder 40. This way the pulley will be positioned at opposite ends of the ladder 40 when the ladder is collapsed and are pulled together by the rope when the system is actuated. the figure also depicts how the rope 50 is coupled to the rest of the system. This rope 50 will have dimensions based on the standards set out in EN 1147:2010 section 7.2 which states that the rope, referred to as the line in the standard has a minimum diameter of 8mm for ladders that require a driving force below 260N to extend, and a minimum radius of 14mm for ladders that require a drive force between 260N and 500N to extend. It is noted that this diameter will determine the diameter needed for the U-shaped channels within the wheels of the system, and will affect the size of other components within the system which are used to guide the rope, such as the side guards 27 and the mounting frame 35. Once the diameter of the rope 50 is chosen the user can ensure that the size of the other components is adjusted appropriately. It is noted that the rope 50 comprises a 3-strand worsted yarn as per the standards for such a system, as this type of yarn provides the desired durability and strength to support the ladder. It is also noted that the yarn may be pre-stretched, this can be preferable as the stretched yarn reduces the elasticity of the worsted yarn. By reducing the elasticity of the rope 50 the amount of force needed to drive the system is reduced as the rope will not stretch before it begins to move. As for the material chosen to create the yarn, there are different considerations the user will need to make. For example, the user will need to choose a material that is not water absorbent, thereby preventing the yarn from absorbing water, from rain or the water that spills from a firefighter’s hose. This is important as the rope 50 will become heavier and may also cause the rope to expand which may cause the rope 50 to become jammed when traveling through the system. Further, if the ladder is being used in firefighting the user may want to choose a material that is heat resistant to prevent the rope from potentially melting when positioned near a burning building. To this end, it is noted that a typical material used for the rope in current systems for firefighter ladders is polyester. Nylon provides a water-resistant yarn that is relatively lightweight, with sufficient strength to endure the driving force applied to the rope 50. However, a preferable material may be nylon 6, as this material is also water-resistant and has similar mechanical properties as nylon 11, however, nylon 6 is more heat resistant than nylon 11, thereby making it more suitable for use in a firefighter’s ladder. In the claimed system one end of the rope 50 will be secured to the ladder 40 via a stirrup 51 attached to the end of the rope 50. It is noted that this stirrup 51 will be attached to a rung of the ladder, preferably the rung above the one that the single wheel pulley 10 is attached to which in the depicted example would be the 20th rung of the ladder. The stirrup 51 will be attached using a suitable fastener such as a rivet. Rivets are preferable as they are typically stronger than other forms of fasteners like a bolt. In the preferred embodiment, the stirrup will be attached using a plurality of rivets to ensure it is attached securely and to limit any lateral movements of the stirrup. In the depicted example the stirrup is secured with six pop rivets. Once the stirrup 51 is secured the user may pass the rope through the other components to form the rope loops that will actuate the ladder 40. When using the components as described above, the rope 50 will follow the following path through the system: first, the rope extends down the ladder passing through the oval aperture 14 in the single wheel pulley 10, then around the smaller secondary wheel 23 of the double wheel pulley. Then the rope 50 goes up the ladder and around the wheel 12 of the single-wheel pulley 10, forming the first loop of rope. Then the rope extends back down the ladder around the larger main wheel 22 of the double wheel pulley 20, ensuring that the outer loop is separated from the first loop by the narrow wall of the side guard 27. Then the loose end of the rope 50 extends up the ladder 40 and over the wheel of the AAD 30 in the direction that ejects the rope 50 out of the back of the AAD 30 in a direction away from the ladder 40 so that the user can pull on the loose end of the rope 50. With this arrangement, the force applied to the rope 50 is exerted to the ladder through the two loops described above which reduces the amount of force required to be applied to the rope 50 to lift the load of the ladder 40 when it is expanding. Figure 6 depicts the complete ladder 40 that incorporates the claimed ladder extending system. It is noted that this ladder 40 is in the collapsed or folded state, as such the components of the system are separated with the single wheel pulley 10 and AAD 30 at the top of the ladder 40 and the double wheel pulley 30 proximate to the bottom of the ladder 40. Is noted that this ladder provides additional features that help to support the ladder 40 when it is extended. These features include the base support 45, comprising the bar and feet at the base of the ladder that helps to lower the ladder’s centre of gravity. The ladder 40 also comprises two support legs 41 or bars that are attached to the side of the ladder and can be folded out to form additional feet, specifically when the support legs 41 are folded out they form an A-shaped frame that provides additional support to the ladder. With these additional support features the user will be able to deploy the ladder swiftly with the claimed system without the risk of the ladder falling over. It is noted that by using the above system the driving force needed to extend the ladder is reduced, this also means if a user applies the same force they would normally apply to a current ladder. The ladder will extend faster which can be important in an emergency situation but also means that ladder support features like the ones described above are more likely to be required. Therefore, the preferable form of the ladder 40 used with the claimed system would include such supporting features to help anchor the ladder and prevent it from falling. Figure 7 depicts examples of the pulleys used in the system that include additional features to help prevent water pooling in the components of the system. In particular, the pulleys 10,20 may include apertures 60 within their respective bases, such that any water on the surface of the pulley may drain through the apertures. Such apertures may also be included in the frame 31 of the AAD 30. It is noted that in the depicted examples all of the pulley wheels 12,22,23,36 are configured to be wider along their edges, creating a recess around the centre of the wheels. This recess helps to reduce the amount of material used in each wheel thereby reducing their mass. However, water can easily pool within these recesses. In some cases, the wheels may also include one or more apertures 61 through the wheel to allow the pooling water to drain. In other cases, the wheels 62 will be configured to have a flat profile so that when the ladder is upright any water will simply slide off the wheels as there will be no recesses where water can pool. These anti-pooling features can be very important when the system is being used by firefighters. Not only does the water increase the risk of wear or rust on the system components but when the ladder is proximate to a burning building this pooled water may be heated into steam which may be hazardous to the individuals on the ladder. If the individual is not wearing protective gear they may be burned by the steam, and even if they are protected the stream may impede the person's vision as they are using the ladder. It is noted that the claimed invention also includes a kit of parts that can be used to form the claimed invention and / or retrofit the claimed system onto an existing ladder. In its simplest 5 form, the kit would comprise the pulleys 10,20 and AAD 30 used in the system as described above. A user may use such a kit to retrofit the system onto an existing ladder, removing the current pulleys and AAD and replacing them with the components in the kit. It is noted that this kit may also comprise all of the fasteners necessary to couple these components to a ladder. Some kits may also include a rope 50 as described above to ensure the rope is the 10 appropriate size for the recessing in the pulley wheels. The kit may further comprise a ladder 40, like the multi-tier ladder depicted in Figure 6. Such kits would be utilised by individuals who do not have a suitable ladder to retrofit the system. In some cases, this kit of parts may also include the appropriate tools for coupling the claimed system to a ladder. These tools may include screwdrivers, spanners or similar tools 15 needed to fasten the various fasteners used to couple the components of the system together. The system may also include a drill for forming holes within the appropriate rung of the ladder to attach the system, however, if the ladder came as part of the kit, then such apertures may already be formed within the rungs 42 of the ladder 40. Lastly, the kit may include a rivet gun for attaching the rivets to the stirrup 52 to the ladder 40.

Claims

1. A ladder extension system configured to be coupled to a layered ladder to extend one or more of the layers, the system comprising;a pair of pulleys located at opposing ends of one of the ladder layers, the first pulley comprises a single pulley wheel configured to rotate in a direction parallel to the plane of the ladder rungs coupled to a frame, wherein the frame comprises a rope aperture for receiving a rope before it is wrapped around the pulley wheel;the second pulley comprises a pair of pulley wheels configured to rotate in a direction parallel to the plane of the ladder rungs coupled to a frame, wherein the pair of wheels is displaced laterally such that a rope can wrap around each wheel to form separate rope loops;an auto-arrest device, or AAD, coupled to a point of the ladder proximate to the first pully, wherein the AAD comprises a frame with a pulley wheel coupled to the frame configured to rotate in a direction perpendicular to the plane of the ladder, and a locking member positioned proximate the wheel coupled to a spring, wherein when the spring is not contracted the locking member is pushed into a first position that is configured to apply force to the wheel to prevent it from turning, and wherein when force is applied to contract the spring the locking member is moved to a second position that frees the wheel to rotate; anda rope, with a first end configured to be anchored to a ladder via a stirrup, and loose at a second end wherein the length of the rope is passed through the pulley wheels of the pulleys and AAD such that pulling on the loose end of the rope will extend the layered ladder.

2. The ladder extension system of claim 1, wherein each of the pulley wheels of the pair of pulleys and the AAD comprises wheels and the rope is made from a Nylon polymer.

3. The ladder extension system of claim 2, wherein the pulley wheels are made from either Nylon 6 or Nylon 11.

4. The ladder extension system of claims 1 to 3 wherein the pulley wheels comprise a profile around their circumference, wherein the edges of the profile are raised relative to the centre of the profile5. The ladder extension system of any preceding claim wherein the pulley wheels comprise gripping features along their circumference, wherein the gripping features comprise at least one of a plurality of grooves, trenches or protrusions.

6. The ladder extension system of any preceding claim wherein the sides of the pulley wheels comprise a flat profile surface.

7. The ladder extension system of claims 1 to 5, wherein the sides of the pulley wheel comprise a recessed trench configured to reduce the overall mass of the pulley wheel, and wherein the trench comprises at least one aperture to allow liquids to drain from the trench.

8. The ladder extension system of claim 7, wherein the pulley wheels comprise a Nylon polymer cover that covers the open end of the trench.

9. The ladder extension system of any preceding claim wherein the AAD comprises a sheath configured to at least partially surround the spring such that the spring can expand and contract but cannot move laterally within the AAD.

10. The ladder extension system of any preceding claim, wherein the pulley frame comprises one or more guiding walls coupled to at least one side of the frame, and configured to guide the rope around the pulley wheels coupled to the frame.

11. The ladder extension system of any preceding claim, wherein the pulley frames comprise a face plate that is configured to cover at least a portion of the pulley wheels coupled to the frame, wherein the face plate comprises an aperture configured to receive a fastener that is passed through the pulley wheels to couple the plate and wheel to the frame.

12. The ladder extension system of claim 11, wherein the aperture in the face plate is a non-circular shape, and the head of the fastener includes a boss with the same shape as the aperture such that the fastener cannot rotate within the aperture.

13. The ladder extension system of any preceding claim, wherein the frame of the pulley and AAD are made of aluminium or an aluminium alloy.

14. The ladder extension system of any preceding claim, wherein the frame of the pulleys and AAD comprise apertures to allow liquid to drain through the frame.

15. The ladder extension system of any preceding claim wherein the rope aperture of the first pulley has an oval shape.

16. The ladder extension system of any preceding claim wherein the wheels of the second pulley are displaced vertically, which refers to a direction parallel to the elongated axis of the ladder the system is coupled to, such that the first upper wheel is closer to the first pulley relative second lower wheel, and wherein the upper wheel has a smaller diameter than the lower wheel.

17. The ladder extension system of any preceding claim wherein the AAD comprises a protective plate that is configured to be coupled to the frame of the AAD in a position that covers at least a portion of the wheel of the AAD, such that the rope is positioned between the plate and the wheel.

18. A fire ladder comprising a plurality of layers, each layer comprising a plurality of steps and configured to slide over each other, and the ladder extension system of claims 1 to 17.

19. The fire ladder of claim 18 wherein the ladder further comprises two support legs, wherein one end of the support leg is coupled to a side of the ladder and is configured to allow the leg to pivot about the coupled end.

20. A method of using the ladder extension system of claims 1 to 17 to extend a layered ladder, the method comprising the steps of:pulling the end of the rope remote from the ladder, such that the rope is under tension, the tension of the rope opens the AAD;continue to pull the rope, causing the pulley wheels to rotate, and pull the second pulley towards the first pulley and AAD, such that the moving pulley extends the sliding layer of the layered ladder.

21. The method of claim 20, further comprising steps to collapse the extended layer ladder, the method comprising the steps of;pulling the end of the rope remote from the ladder such that the rope is under tension, opening the AAD,pushing the rope slowly towards the ladder, feeding the rope back into the AAD to rotate the pulley wheel in the opposite direction, extending the rope loop between the pulleys,lowering the second pulley away from the first pulley and AAD, thereby collapsing the layer of the layered ladder.

22. A kit of parts comprises the ladder extension system of claims 1 to 17, comprising a one-wheel pulley, a two-wheel pulley, an AAD, a polymer rope and a stirrup, with fasteners configured to attach the components to a layered ladder, and rivets to couple the stirrup to one end of the rope.

23. The kit of parts of claim 22 further comprising the layered ladder of claims 16 and 17.

24. The kit of part of claims 22 and 23 further comprises tools configured to couple the component of the extension system to the layered ladder, via the fasteners and rivets.

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