Drainage port for a transfer pump and a method of using the same

Abstract

A positive displacement pump 100 having a preferred operating orientation relative to gravity, comprising a cavity (fig.2, 150) and a drainage system (fig.2, 180) configured for removing liquid and / or gas from a lower section of the cavity while the pump is in its preferred operating orientation relative to gravity. The drainage system may be in the lowermost section of the cavity. There may be two or more drainage systems on opposite ends of the cavity. A method of removing a liquid and gas mixture from a positive displacement pump using the drainage system described.

Description

Technical Field The present disclosure relates to a drainage port for a transfer pump and a method of using the same, and particularly, but not exclusively, to a drainage port for a transfer pump for unidirectional pumping of a liquid. Background Transfer pumps are widely used in various different fields to move liquids. However, there is always a need for improvement in efficiency in pumps to improve fluid transfer rates. There is therefore a need for a transfer pump that can both efficiently keep up with the increased demand for fluid transfer and can effectively run uninterrupted without the need for constant maintenance. The present invention results from Applicant’s work in using a drainage port to improve the efficiency of their transfer pump by removing unwanted liquid and / or gas from the transfer pump. Summary According to a first aspect of the current disclosure, there is provided a positive displacement pump having a preferred operating orientation relative to gravity, and comprising a cavity. The positive displacement pump further comprising a drainage system for removing liquid and / or gas from a lower section of the cavity while the pump is in its preferred operating orientation relative to gravity. Removing liquid from a lower section of the cavity reduces build-up of unwanted moisture in the pump cavity. Unwanted moisture can reduce the efficiency of the pump leading to loss of pumping pressure. Optionally, the preferred operating orientation relative to gravity is such that the drainage system is located at the lower section of the cavity. In its preferred operating orientation relative to gravity, the pump is orientated such that a shuttle assembly is located at the top of the pump, and the drainage system is located at the bottom of the cavity. This operating orientation ensures that the drainage system is located at the lower section of the cavity and gravity can act on the liquid within the cavity to bring it to the lower section of the cavity. Optionally, the positive displacement pump is orientated such that drainage system is located on a ground-facing side of the positive displacement pump. Optionally, the cavity is configured to accommodate an actuating piston, wherein the actuating piston is configured to reciprocally move between two extremities of the cavity. Optionally, the cavity is centrally located between two valve assemblies configured to unidirectionally pump a liquid. Optionally, the drainage system is located at a lowermost section of the cavity. The piston is configured to sweep the lowermost internal surface of the cavity. Having the drainage system at the lowermost section of the cavity allows the sweeping motion of the piston to drain the liquid and / or gas out of the drainage system. Optionally, the drainage system only removes liquid from the cavity of the positive displacement pump. Optionally, the drainage system drains liquid and / or gas from a lowermost section of the cavity when the positive displacement pump is in its preferred operating orientation relative to gravity. Liquid and / or gas will usually build up in the lowermost section of the cavity due to gravitational forces. Locating a drainage system at the lowermost section of the cavity will result in more efficient removal of unwanted liquid and / or gas from the cavity. Optionally, the drainage system is configured to separate a drained liquid and gas mixture into a separated gas portion and a separated liquid portion. Separating the liquid from the drained liquid and gas mixture allows the separated air to be recycled back into the positive displacement pump, ensuring minimal pressure loss in the cavity of the positive displacement pump. Optionally, the positive displacement pump comprises two or more drainage systems. Two drainage systems located on either side of the lowermost section of the cavity allows for liquid and / or gas to be removed from both sides of the positive displacement pump. Additionally, this ensures that the gas and / or liquid is equally drained from both sides of the positive displacement pump, helping to maintain a pressure balance between both sides of the cavity during operation. Optionally, the one or more drainage systems each comprise a drainage port. Optionally, the one or more drainage ports comprise a one-way valve configured such that the drained liquid and / or gas only travels out of the cavity. During operation of the pump, the reciprocal motion of the piston may draw the liquid and / or gas back into the cavity, therefore, a one way valve at the one or more drainage ports stops the liquid and / or gas from re-entering the cavity after it has been drained. Optionally, the one or more drainage systems each comprise one or more drainage ports, and, the one or more drainage ports may be retrofittable to the positive displacement pump. This allows positive displacement pumps that do not contain a drainage port to be fitted out with one or more drainage ports. Optionally, the two or more drainage systems are located on opposing sides of the cavity. According to a second aspect of the present disclosure, there is provided a method of removing a liquid and gas mixture from a positive displacement pump; the positive displacement pump having a preferred operating orientation relative to gravity, and a cavity within the pump having a lower section when the pump is in its preferred operating orientation relative to gravity, and the cavity having a drainage port in the lower section of the cavity. The method comprises reciprocally moving a piston within the cavity, the movement of the piston pushing the liquid and gas mixture from within the cavity through the drainage port and out of the cavity. Removing liquid from a lower section of the cavity reduces build-up of unwanted moisture in the pump cavity. Unwanted moisture can reduce the efficiency of the pump leading to loss of pumping pressure. Optionally, the drainage port is in a lowermost section of the cavity. Liquid and / or gas will usually build up in the lowermost section of the cavity due to gravitational forces. Locating a drainage system at the lowermost section of the cavity will result in more efficient removal of unwanted liquid and / or gas from the cavity. Optionally, the second aspect further comprises the step of injecting gas into the cavity to cause the reciprocal movement of the piston. Optionally, the cavity comprises first and second drainage ports in the lower section of the cavity, and wherein the movement of the piston pushes the liquid and gas mixture from within the cavity through the two drainage ports and out of the cavity. Two drainage systems located on either side of the lowermost section of the cavity allows for liquid and / or gas to be removed from both sides of the positive displacement pump. Additionally, this ensures that the gas and / or liquid is equally drained from both sides of the positive displacement pump, helping to maintain a pressure balance between both sides of the cavity during operation. Optionally, the reciprocal movement of the piston pushes the liquid and gas mixture from within the cavity alternately through the first and second drainage ports and out of the cavity. This ensures that the gas and / or liquid is equally drained from both sides of the positive displacement pump, helping to maintain a pressure balance between both sides of the cavity during operation. Optionally, the method further comprising the step of separating gas from the drained liquid and gas mixture. Separating the liquid from the drained liquid and gas mixture allows the separated air to be recycled back into the positive displacement pump, ensuring minimal pressure loss in the cavity of the positive displacement pump. Optionally, the method further comprising injecting the separated gas back into the cavity to cause the reciprocal movement of the piston. Recycling the separated gas back into the positive displacement pump ensures minimal pressure loss in the cavity of the positive displacement pump. Optionally, the method further comprising the step of discarding the separated liquid from the mixture of gas and liquid. Discarding the liquid ensures no liquid is recycled back into the positive displacement pump, reducing the moisture levels within the cavity of the positive displacement pump. Optionally, the reciprocal movement of the piston is actuated by a pilot air valve configured to divert an injected gas between a first side of the cavity and second side of the cavity. Optionally, the positive displace pump comprises one or more exhaust valve pins configured to move the pilot air valve between a first configuration wherein it diverts the injected gas to the first side of the cavity and a second configuration wherein it diverts the injected gas to the second side of the cavity. The exhaust valve pins are actuated through contact of the piston during operation. The exhaust valve pins divert a small portion of the pressurized gas from within the cavity back through the pilot air valve, causing it to move between its first and second configurations. Further features and advantages of the first and second aspects of the present disclosure will become apparent from the claims and the following description. Brief Description of Drawings Embodiments of the present disclosure will now be described by way of example only, with reference to the following diagrams, in which:- Figure la shows a schematic cross-sectional view of the positive displacement pump during operation; Figure lb shows the positive displacement pump of Figure la at a different stage during operation; Figure lc shows the positive displacement pump of Figures la and lb at another different stage during operation; Figure 2a is a blown-up view of a central portion of the positive displacement pump of Figure la; Figure 2b is a blown-up view of a central portion of the positive displacement pump of Figure lb; and Figure 2c is a blown-up view of a central portion of the positive displacement pump of Figure lc. Detailed Description Figure la shows a schematic cross-sectional view of a positive displacement pump 100 during operation. In Figure la, the pump 100 is in the process of displacing fluid. The pump comprises a first valve assembly llOi and a second valve assembly 1 lOii. The first valve assembly llOi and the second valve assembly HOii are identical in their functions. The first valve assembly 1101 and the second valve assembly HOii are reflections of each other relative to a central line A-A running down the centre of the pump 100. Each of the valve assemblies llOi, HOii comprises a pressure responsive suction valve 115i, 115ii (hereon referred to as 'suction valve’) and a pressure responsive delivery valve 120i, 120ii (hereon referred to as ‘delivery valve’). The suction valves 115i, 115ii are located on a downward facing portion of the valve assemblies 1 lOi, HOii when the pump 100 is in its preferred operating orientation. The delivery valves 1201, 12011 are located on an upward facing portion of the valve assemblies 1101, llOii when the pump 100 is in its preferred operating orientation. The delivery valves 120i, 120ii are located on opposing sides to the suction valves 115i, 115ii on their respective valves assemblies llOi, llOii. The suction valves 115i, 115ii each comprise a suction ball 116i, 116ii. The suction valves 115i, 115ii each comprise a suction valve cage 117i, 117ii and a suction valve seat 119i, 119ii. The suction valve cage 117i, 117ii is designed to restrain the suction ball 116i, 116ii during inflow of fluid through the suction valve 115i, 115 ii into the valve assemblies 1101, llOii. During outflow of fluid through the delivery valves 120i, 120ii, the suction valves 115i, 115ii remain in a closed configuration in which fluid flow through the suction valve is prevented. During outflow, the suction valve balls 116i, 116ii are forced through pressure and / or gravity into their respective suction valve seats 119i, 119ii, maintaining a seal on the suction valves 115i, 115ii. This ensures that flow through the valve assemblies 1 lOi, llOii is unidirectional. When the positive displacement pump 100 is in its preferred operating orientation, the suction valves 115i, 115ii and delivery valves 120i, 120 ii are configured such that gravity forces their respective suction valve balls 116i, 116ii and delivery valve balls 121i, 121ii into their respective suction valve seats 119i, 119ii and delivery valve seats 124i, 124ii. By responding to gravity, the suction valves 115i, 115ii and delivery valves 120i, 120ii can return to their respective closed configurations faster, thus increasing efficiency in terms of power used to pump the fluid and in terms of backflow. The delivery valves 120i, 120ii each comprise a delivery valve ball 12li, 12 lii. The delivery valves 12Oi, 12Oil each comprise a delivery valve cage 122i, 122ii and a delivery valve seat 124i, 124ii. The delivery valve cage 122i, 122ii is designed to restrain the delivery valve ball 12li, 12lii during outflow of fluid from the valve assemblies llOi, llOii through the delivery valve 120i, 120ii. During inflow of fluid through the suction valves 115i, 115ii, the delivery valves 120i, 12 Oii need to remain closed and sealed up. During inflow, the delivery valve balls 121i, 12111 are forced through pressure and / or gravity into their respective delivery valve seats 124i, 124ii, maintaining a seal on the delivery valves 120i, 12011 The pump 100 further comprises a piston 125 located centrally between the two valve assemblies llOi, llOii. The piston 125 reciprocally moves from side to side between the two valve assemblies 1101,1 lOii. The piston 125 is connected to a shaft 127 which extends in both directions away from the piston 125 towards the two valve assemblies llOi, llOii. The reciprocal motion of the piston 125 will be described in more detail later on. Each end of the shaft 127 is connected to a rigid plate 130i, 130ii. The rigid plates 1301 130ii on each side of the shaft 127 are designed to draw fluid into / expel fluid out of the valve assemblies 1101 llOii during operation. When the piston 125 moves towards valve assembly 110i, rigid plate 13Oi is expelling fluid from valve assembly 110i, and rigid plate 13Oil is drawing fluid into valve assembly llOii. Likewise, when the piston 125 moves away from valve assembly llOi, rigid plate 130i is drawing fluid into valve assembly llOi, and rigid plate 13 Oii is expelling fluid out of valve assembly llOii. The reciprocal motion of the piston 125 connected to the rigid plates 130i, 130ii via the shaft 127 means one of the valve assemblies llOi, llOii will be drawing fluid into itself through its respective suction valve 115i, 115ii, whilst the other valve assembly llOi, llOii will be expelling fluid out of itself through its respective deliveiy valve 12 Oi, 12 Oii. The pump 100 further comprises flexible seals 135i, 135ii. The flexible seals 135i, 135ii are fixed to the rigid plates 130i, 130ii, creating a seal between the fluid being drawn into / expelled out of the valve assemblies 115i, 115ii and the space which the piston 125 and shaft 127 occupy. The flexible seals 135i, 135ii are designed to flex during the reciprocal motion of the piston 125 and the rigid plates 13 Oi, 130ii. Figure la shows the pump 100 during operation wherein the piston 125 is at a fully extended position towards the second valve assembly 115ii and away from the first valve assembly 115i. In this instance the second valve assembly 115ii has just expelled fluid through its delivery valve 12Oii. The delivery valve ball 121ii is sitting in its open configuration in its delivery valve cage 122ii, allowing fluid to pass through the delivery valve 120ii. The suction valve ball 116ii is sitting in its closed configuration in its suction valve seat 119ii, creating a seal that stops any fluid from passing through the suction valve 115ii. Furthermore, at the same time, the first valve assembly 115i has just drawn fluid through its suction valve 1151 The suction valve ball 116i is sitting in its suction valve cage 117i, allowing fluid to pass through the suction valve 1151 The delivery valve ball 120i is sitting in its delivery valve seat 124i, creating a seal that stops any fluid from passing through the delivery valve 1201 Figure lb shows the pump 100 directly after its position in Figure la. In Figure lb, the piston 125 moves away from the second valve assembly 115ii towards the first valve assembly 1151 The movement of the piston 125 decreases the pressure in the second valve assembly HOii drawing fluid into the second valve assembly 11 Oh through the suction valve 115ii. At this instance, the suction valve ball 116ii is sitting in its open configuration in its suction valve cage 117ii, allowing fluid to flow through the suction valve 115ii. At the same time, the delivery valve ball 121ii is sitting in its closed configuration in its delivery valve seat 124ii, creating a seal at the delivery valve 12 Oh, ensuring that no fluid escapes. At the same time, whilst fluid is being drawn into the second valve assembly 11 Oii, fluid is being expelled out of the first valve assembly 11 Oi. The piston 125 moving towards the first valve assembly llOi reduces the volume available for fluid and increases the pressure in the first valve assembly 1101, causing fluid to be expelled through the delivery valve 120i. The suction valve 115i is in a closed configuration and the delivery valve 12 Oi is in an open configuration. The suction valve ball 116i is sitting in its suction valve seat 119i, creating a seal at the suction valve 116i, ensuring that no fluid escapes. The delivery valve ball 12 li is sitting in its delivery valve cage 122i, allowing fluid to exit through the delivery valve 120i. Figure 1c shows the pump 100 directly after its position in Figure lb. In Figure lb, the piston 125 is at a fully extended position towards the first valve assembly 115i and away from the second valve assembly 115ii. In this instance the first valve assembly 115i has just expelled fluid through its delivery valve 120i. The delivery valve ball 12li is sitting in its open configuration in its delivery valve cage 12 2i, allowing fluid to pass through the delivery valve 120i. The suction valve ball 116i is sitting in its closed configuration in its suction valve seat 119i, creating a seal that stops any fluid from passing through the suction valve 115i. Furthermore, at the same time, the second valve assembly 115ii has just drawn fluid through its suction valve 115ii. The suction valve ball 116ii is sitting in its open configuration in its suction valve cage 117ii, allo wing fluid to pass through the suction valve 115ii. The delivery valve ball 120ii is sitting in its closed configuration in its delivery valve seat 124ii, creating a seal that stops any fluid from passing through the delivery valve 120ii. This reciprocating process continues, constantly drawings fluid through the suction valves 115i, 115ii and expelling it through the delivery valves 120i, 120ii. Turning now to Figure 2a, there is shown a blown-up view of a central portion of the positive displacement pump 100 during operation as shown in Figure la. The pump 100 defines a cavity 150 and further comprises a piston 125 located with the cavity 150. During operation, the piston is reciprocally moved between a fully extended position on the right (as shown in Figure 2a) of the cavity 150 and a fully extended position on the left (as shown in Figure 2c) of the cavity 150. The pump 100 further comprises a first aperture 160 and a second aperture 165. The first and second apertures 160, 165 both connect the cavity 150 to a shuttle assembly 170. In Figure 2a, the shuttle assembly 170 has injected gas through the first aperture 160 into the cavity 150, pushing the piston 125 towards the right side of the cavity 150. As the piston 125 is pushed towards the right side of the cavity 150, gas that was previously in the cavity 150 is exhausted through the second aperture 165 back into the shuttle assembly 170. The pump 100 further comprises a first drainage system 180 and a second drainage system 185, both located at a lower section of the cavity 150. The first drainage system 180 comprises a first drainage port 181 and the second drainage system 185 comprises a second drainage port 186. The first drainage port 181 and second drainage port 186 are both in bi-directional fluid connection with the cavity 150. During operation, a fluid portion of the exhausted gas and / or liquid is filtered out of the exhausted gas and / or liquid, ensuring that any flow of gas back through the first and second drainage ports 181, 186 no longer comprises liquid. Alternatively, the first drainage port 181 and second drainage port 186 may both comprise one-way valves, such as check valves, that only allow the liquid and / or gas to travel unidirectionally outward from the cavity 150. The first drainage port 181 and second drainage port 186 may be a ball check valve, diaphragm check valve, swing check valve, or any other suitable alternative. The first drainage port 181 and second drainage port 186 are both configured such that liquid and / or gas can be removed from the cavity 150 without requiring additional input of force from the pump 100. Additionally, the first drainage port 181 and second drainage port 186 may both be configured such that liquid and / or gas can not be drawn back into the cavity 150 through either one of the first drainage port 181 and second drainage port 186. The first and second drainage systems 180, 185 remove liquid and / or gas from a lower section of the cavity 150 while the pump 100 is in its preferred operating orientation relative to gravity. In Figure 2a, as the piston 125 is pushed towards the right side of the cavity 150, the piston 125 sweeps a lowermost internal surface 190 of the cavity 150, pushing liquid and / or gas out of the second drainage port 186. Turning now to Figure 2b, there is shown a blown-up view of a central portion of the positive displacement pump 100 during operation as shown in Figure lb. The shuttle assembly 170 is now injecting gas into the cavity 150 through the second aperture 165, causing the piston 125 to move from the right side of the cavity 150 towards the left side of the cavity 150. As the piston 125 moves towards the left side of the cavity 150, air is exhausted out of aperture 160 into the shuttle assembly 170. As the piston 125 moves towards the left side of the cavity 150, the piston 125 sweeps the lowermost internal surface 190 of the cavity 150, causing any liquid within the cavity to build up at the lowermost end of the piston 125. This sweeping then pushes liquid and / or gas out of the first drainage port 181. Turning now to Figure 2c, there is shown a blown-up view of a central portion of the transfer pump 100 during operation as shown in Figure 1c. The shuttle assembly 170 is still pumping air into the cavity 150 through the second aperture 165, causing the piston 125 to move from the right side of the cavity 150 towards the left side of the cavity 150. The piston 125 has now moved towards the leftmost extremity of the cavity 150, resulting in all of the air on the left side of the piston 125 being exhausted out of aperture 160 into the shuttle assembly 170. As the piston 125 moves towards the left side of the cavity 150, the piston 125 sweeps the base 190 of the cavity 150 pushing liquid and / or gas out of the first drainage port 181. Once the piston 125 has reached its leftmost position (as shown in Figure 2c) within the cavity 125, all of the liquid and / or gas built up on the left side of the piston 12 5 is removed through the first drainage port 181. The reciprocal motion of the piston 125 is caused by alternating the direction of the flow of gas being injected into the cavity 150 through the first and second apertures 160,165. As the direction of gas flow is changed, the piston 125 moves from side to side within the cavity 150, allowing the valve assemblies llOi, HOii to pump liquid. Likewise, the movement of the piston 125 from side to side pushes liquid and / or gas out of the first and second drainage ports 181, 186. This results in liquid and gas mixture being alternately drained from the cavity 150 through the first and second drainage ports 181,186 out of the cavity. Once the gas and / or liquid is drained from the first and second drainage ports 181,186, the gas and / or liquid is pushed through a filter and the liquid portion is separated from the gas portion. The gas portion is then recycled back into the shuttle assembly 170 through one of the first or second apertures 160,165 and injected back into the cavity 150 through either one of the first and second apertures 160, 165. The liquid portion is discarded. Recycling the gas portion ensures that there is no pressure loss within the shuttle assembly 170 and cavity 150, resulting in improved efficiency. The reciprocal motion of the piston 125 is controlled by alternating which one of the first and second apertures 160, 165 the gas is injected into the cavity 150 through. This is controlled by the shuttle assembly 170 which comprises a pilot air valve 171. The pilot air valve 171 is moved between a left configuration and a right configuration. When in its left configuration, the pilot air valve 171 creates a direct flow path between the pressurized gas inlet and the first aperture 160. Likewise, when in its left configuration, the pilot air valve 171 creates a direct flow path between the second aperture 165 and a gas exhaust. The left configuration of the pilot air valve 171 permits gas to enter the cavity 150 through the first aperture 160, pushing the piston 125 towards the right side of the cavity 150. As the right side of the cavity 150 is now in a direct flow path with the gas exhaust, it is no longer under pressure, and, therefore, the force of the piston 125 being pushed towards the right side of the cavity 150 forces the gas out of the second aperture 165 and the second drainage port 186. Once the piston 125 has reached its fully extended position towards the right side of the cavity 150, the piston 125 contacts a first exhaustvalve pin (not shown). This contact opens up a flow path for the gas within the cavity 150 back towards the pilot air valve 171. Pressurized gas now travels back towards the pilot air valve 171, causing it to displace to its right position. When the pilot air valve 171 is in its right position, a direct flow path is created between the pressurized gas inlet and the second aperture 165. Likewise, when in its right configuration, the pilot air valve 171 creates a direct flow path between the first aperture 160 and the gas exhaust. The right configuration of the pilot air valve 171 permits gas to enter the cavity 150 through the second aperture 165, pushing the piston 125 towards the left side of the cavity 150. As the left side of the cavity 150 is now in a direct flow path with the gas exhaust, it is no longer under pressure, and, therefore, the force of the piston 125 being pushed towards the left side of the cavity 150 forces the gas out of the first aperture 160 and the first drainage port 181. Once the piston 125 has reached its fully extended position towards the left side of the cavity 150, the piston 125 contacts a second exhaust valve pin (not shown). This contact opens up a flow path for the gas within the cavity 150 to travel back towards the pilot air valve 171. Pressurized gas now travels back towards the pilot air valve 171, causing it to displace to its left position. The gas exiting the pilot air valve 171 through the gas exhaust is then passed through an air regulator permitting the gas to be recycled and reused. Alternatively, the gas exiting the gas exhaust is vented to the atmosphere and new gas is brought in to create the reciprocal movement of the piston 125. Alternatively, the gas exhaust is valve actuated creating a controlled pressurized environment with the pump 100. It will be appreciated that other methods of controlling gas flow between the gas inlet and the cavity may be used. Different configurations of the pilot air valve may be used. During exhaustion of gas from either side of the cavity 150, gas and / or liquid is forced through either the first or second drainage ports 181,186. The gas portion of the exhausted gas and / or liquid exhausted through the first drainage port 181 is in fluid connection with the first aperture 160 through a passage 161 on the side of the first aperture 160. The gas portion exhausted out of the first drainage port 181 is exhausted out of the cavity at the same time as the gas exhausted through the first aperture 160. The fluid connection between the first drainage port 181 and the first aperture 160 ensures pressure is maintained between all the gas and / or liquid on the left side of the piston 125 at any given time. Likewise, the gas portion of the exhausted gas and / or liquid exhausted through the second drainage port 186 is in fluid connection with the second aperture 165 through a passage 166 on the side of the second aperture 165. The gas portion exhausted out of the second drainage port 186 is exhausted out of the cavity at the same time as the gas exhausted 5 through the second aperture 165. The fluid connection between the second drainage port 186 and the second aperture 165 ensures pressure is maintained between all the gas and / or liquid on the right side of the piston 125 at any given time. Although particular embodiments of the disclosure have been disclosed herein in detail, 10 this has been done by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the summary / appended claims. It is contemplated by the inventors that various substitutions, alterations, and 15 modifications may be made to the invention without departing from the scope of the invention as defined by the summary / claims.

Claims

1. A positive displacement pump having a preferred operating orientation relative to gravity, the positive displacement pump comprising:a cavity; anda drainage system configured for removing liquid and / or gas from a lower section of the cavity while the pump is in its preferred operating orientation relative to gravity.

2. The positive displacement pump of claim 1, wherein the drainage system drains liquid and / or gas from a lowermost section of the cavity when the positive displacement pump is in its preferred operating orientation relative to gravity.

3. The positive displacement pump of any preceding claim, wherein the cavity is configured to accommodate an actuating piston, and wherein the actuating piston is configured to reciprocally move between two extremities of the cavity.

4. The positive displacement pump of any preceding claim, wherein the cavity is centrally located between two valve assemblies configured to unidirectionally pump a liquid.

5. The positive displacement pump of any preceding claim, wherein the drainage system is located at a lowermost section of the cavity.

6. The positive displacement pump of any preceding claim, wherein the drainage system is configured to separate a drained liquid and gas mixture into a separated gas portion and a separated liquid portion.

7. The positive displacement pump of any preceding claim, wherein the positive displacement pump comprises two or more drainage systems.

8. The positive displacement pump of claim 8, wherein the two or more drainage systems are located on opposing sides of the cavity.

9. The positive displacement pump of any preceding claim, wherein the one or more drainage systems each comprise a drainage port.

10. A method of removing a liquid and gas mixture from a positive displacement pump; the positive displacement pump having a preferred operating orientation relative to gravity, and a cavity within the pump having a lower section when the pump is in its preferred operating orientation relative to gravity, and the cavity having a drainage port in the lower section of the cavity, the method comprising: reciprocally moving a piston within the cavity, the movement of the piston pushing the liquid and gas mixture from within the cavity through the drainage port and out of the cavity.

11. The method of claim 10, wherein the drainage port is in a lowermost section of the cavity.

12. The method of claim 10 or 11, further comprising the step of injecting gas into the cavity to cause the reciprocal movement of the piston.

13. The method of any one of claims 10 to 12, wherein the cavity comprises first and second drainage ports in the lower section of the cavity, and wherein the movement of the piston pushes the liquid and gas mixture from within the cavity through the two drainage ports and out of the cavity.

14. The method of claim 13, wherein the reciprocal movement of the piston pushes the liquid and gas mixture from within the cavity alternately through the first and second drainage ports and out of the cavity.

15. The method of any one of claims 10 to 14, the method further comprising the step of separating gas from the drained liquid and gas mixture.

16. The method of claim 15, the method further comprising injecting the separated gas back into the cavity to cause the reciprocal movement of the piston.

17. The method of claim 15 or 16, the method further comprising the step of discarding the separated liquid from the mixture of gas and liquid.

18. The method of any one of claims 10 to 17, wherein the reciprocal movement of the 5 piston is actuated by a pilot air valve configured to divert an injected gas between a first side of the cavity and second side of the cavity.

19. The method of claim 18, wherein the positive displace pump comprises one or more exhaust valve pins configured to move the pilot air valve between a first configuration 10 wherein it diverts the injected gas to the first side of the cavity and a second configuration wherein it diverts the injected gas to the second side of the cavity.

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