Method and apparatus for filtering hydraulic fluid

Abstract

The invention provides a hydraulic fluid filtration system and method of use. The system comprises two or more vessels, a filter system comprising at least one filter arranged between the two or more vessels and a valve system. The valve system is operable transfer hydraulic fluid between the two or more vessels through the at least one filter.

Description

[0001] Method and Apparatus for Filtering Hydraulic Fluid

[0002] The present invention relates to hydraulic fluid systems and in particular to apparatus and methods for filtering hydraulic fluid. Aspects of the invention relate to apparatus and methods for filtering hydraulic fluid which may be used in a hydraulic fluid system.

[0003] Background to the Invention

[0004] Hydraulic fluid is essential for the operation of machinery and engine components. Hydraulic fluid is a non-compressible fluid which is used to transfer power, lubricate and protect components within hydraulic machinery and eguipment.

[0005] Current hydraulic systems reguire large volumes of hydraulic fluid which over time may become contaminated by wear debris due to mechanical erosion, pitting, spalling, fatigue and / or corrosion of machinery components. Hydraulic fluid may also become contaminated by infiltration of foreign particles, chemicals and / or water.

[0006] The contamination of hydraulic fluid can result in fluid degradation which limits its ability to transfer power, lubricate and protect machinery components. In an enclosed hydraulic system contaminant particles continuously circulate many thousands of times over a period of years. This may result in damage to the hydraulic system, decreased efficiency, system failures and considerable downtime for expensive repairs.

[0007] The contaminated hydraulic fluid has to be drained from the system and discarded. The removed fluid is replaced by new fluid. This fluid replacement operation may be reguired multiple times each year depending on the usage of the hydraulic system. The regular replacement of fluid and disposal of contaminated fluid is expensive and can create significant environmental issues.

[0008] It is known to provide a hydraulic fluid filter in a hydraulic system. Typically the hydraulic fluid filter is located on a high pressure, suction or return line and the hydraulic fluid passes through the filter before the hydraulic fluid is stored in a hydraulic fluid storage tank. However, over time the filter can become blocked or degraded which can further damage the hydraulic system as the blocked or degrading filter can result in foreign particles being released into the hydraulic system. Summary of the Invention

[0009] It is an object of an aspect of the present invention to obviate or at least mitigate the disadvantages of prior art hydraulic fluid filtration apparatus and methods.

[0010] It is an object of an aspect of the present invention to provide a robust, reliable and compact hydraulic fluid filtration apparatus and method of use.

[0011] It is another object of an aspect of the present invention to provide a hydraulic fluid filtration apparatus configured to be integrated in or connected to a hydraulic system of a piece of equipment.

[0012] It is a further object of an aspect of the present invention to provide a hydraulic fluid filtration apparatus and method of improving the purity of hydraulic fluid before, during and / or after it is used in a hydraulic system of a piece of equipment.

[0013] It is another object of the invention to provide a method of filtering hydraulic fluid before, during and / or after it is used in a hydraulic system of a piece of equipment.

[0014] Further aims of the invention will become apparent from the following description.

[0015] According to a first aspect of the invention, there is provided a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; and a valve system; wherein the valve system is operable to transfer hydraulic fluid between the two or more vessels through the at least one filter.

[0016] The valve system may be configured to control the transfer of hydraulic fluid back and forth between the two or more vessels through the at least one filter. The valve system may be configured to control the alternating transfer of hydraulic fluid between the two or more vessels through the at least one filter. The valve system may be configured to control reciprocating flow of hydraulic fluid back and forth between the two or more vessels through the at least one filter. The valve system be configured to alternate the flow direction of hydraulic fluid back and forth between the two or more vessels through the at least one filter.

[0017] The system may be configured to cycle hydraulic fluid back and forth between the two or more vessels through the at least one filter until a desired cleanliness level of the hydraulic fluid has been reached.

[0018] The valve system may be configured to select at least one filter to pass hydraulic fluid through. The hydraulic fluid filtration system may comprise a control unit configured to control the actuation of one or more valves in the valve system. The control unit may be configured to control reciprocating flow of hydraulic fluid back and forth between the two or more vessels through the at least one filter. The control unit be configured to alternate the flow direction of hydraulic fluid back and forth between the two or more vessels through the at least one filter. The at least one filter may be arranged in a flow path between the two or more vessels. The at least one filter may have a micron rating selected from the range of 10nm to 100pm. The micron rating may be selected from the range of 100nm to 25pm.

[0019] The system may comprise at least one pump. The at least one pump may be a fluid pump, impeller or thruster. The at least one pump may be a reversible pump. The at least one pump may be configured to pump hydraulic fluid between the two or more vessels through the at least one filter at a flow rate range of between 0.1 to 200 litres per minute. The flow rate range may be between 1 to 10 litres per minute.

[0020] The control unit may be configured to generate a control signal to the at least one pump to control the flow of hydraulic fluid between the two or more vessels through the at least one filter.

[0021] The system may comprise at least one heating device. The heating device may be configured to increase the temperature of the hydraulic fluid to a desired temperature. The heating device may be configured to increase the temperature of the hydraulic fluid to a desired temperature to assist in the removal of water and / or air from the hydraulic fluid. Circulating hydraulic fluid may pass through at least a part of the heating device to heat the hydraulic fluid. The heating device may be incorporated into the at least one filter or a housing of at least one filter. The at least one heating device may be an electrical heater, friction generating device and / or a heat exchange device. The friction generating device may comprise a valve operable to create heat by increasing internal fluid friction in the fluid and thereby raising its temperature. The electrical heater may be configured to heat a buffer fluid and raise the hydraulic fluid temperature by forced convection and / or parallel or counter flows of the heated buffer fluid and the hydraulic fluid. The at least one heating device may comprise a tube conveying a heating fluid such as water in parallel or counterflow.

[0022] The system may comprise at least one cooling device. The cooling device may be configured to reduce the temperature of the hydraulic fluid to a desired temperature. The cooling device may be configured to reduce the temperature of the hydraulic fluid to a desired temperature to assist in the removal of water and / or air or another fluid or phase from the hydraulic fluid. Circulating hydraulic fluid may pass through at least a part of the cooling device to cool the hydraulic fluid. The cooling device may be incorporated into the at least one filter or a housing of at least one filter. The at least one cooling device may be a Peltier cooling device. The at least one cooling device may be a powered cooling source such as a heat pump. The at least one cooling device may be a heat exchanger. The at least one cooling device may comprise a tube conveying a cooling fluid such as water in parallel or counterflow.

[0023] The system may comprise at least one cooling device and / or at least one heating device. The temperature of the hydraulic fluid may be increased and / or reduced at different stages of filtration. The system may be configured to control and / or adjust the temperature of the hydraulic fluid. The system may be configured to control and / or adjust the temperature of the hydraulic fluid at different stages of filtration. The temperature of the hydraulic fluid may be first increased and then reduced. The temperature of the hydraulic fluid may be first reduced and then increased. The temperature of the hydraulic fluid may be increased and / or reduced to assist in the removal of water and / or air from the hydraulic fluid.

[0024] The temperature of the hydraulic fluid may be increased and / or reduced to reduce the fluid viscosity and / or allow an otherwise high viscosity fluid to be processed.

[0025] Each of the vessels may comprise at least one inlet and at least one outlet. At least one valve may be configured to selectable open a pathway between at least one vessel outlet and at least one filter inlet. At least one valve may be configured to selectable open a pathway between at least one filter inlet and a first vessel outlet or a second vessel outlet. At least one valve may be configured to selectable open a pathway between at least one filter outlet and at least one vessel inlet. At least one valve may be configured to selectable open a pathway between at least one filter outlet and a first vessel inlet or a second vessel inlet.

[0026] The at least one filter may comprise a filter housing. The filter housing may comprise a magnet. The filter housing may comprise an electromagnet. The magnet or electromagnet may be configured to attract ferrous particles to the magnet or electromagnet.

[0027] The electromagnet may be operable between a first condition where the electromagnet is active and attracts ferrous particles in the fluid to the electromagnet, and a second condition when the electromagnet is inactive and ferrous particles in the fluid are not attracted to the electromagnet.

[0028] The hydraulic fluid filtration system may comprise at least one sensor. The at least one sensor may be selected from the group including particle counter, humidity sensors, light sensor, optical sensor, capacitance sensor, flow meter, density sensor, viscosity sensor, pressure sensor, temperature sensor, liquid level indicators, ultrasonic sensor, magnetostrictive sensor, level probes, rod sensor, limit sensor, level and fill level switches, spectroscopy sensor, optical spectrometry sensor and / or float switches. The particle counter may be a digital, laser and / or a camera particle counter.

[0029] The system may comprise apparatus to assist in the removal of air from the hydraulic fluid. The system may comprise an ultrasonic device such as an ultrasonic transducer. The ultrasonic device may be configured to transmit pulse waves or vibrational waves through at least a part of the hydraulic fluid. The pulse waves or vibrational waves may be configured to remove dissolved gasses and / or entrained air bubbles from the hydraulic fluid. The system may comprise a degassing device to remove air and / or gas from the hydraulic fluid. The degassing device may be selected from the group comprising vortex separator, cyclone separator, vacuum degasser, fluid agitator, deaerator and / or centrifugal deaerator.

[0030] The geometry of the system may be designed to assist air rising out from the fluid. The geometry of the system may be designed to minimise the creation or maintenance of bubbles in the hydraulic fluid. The diameter of tubing, inlets and / or outlets may be configured to minimise bubble flow effect in hydraulic fluid. The shape of the tubing, inlets and / or outlets may be selected to minimise bubble flow effect in hydraulic fluid. The shape of the tubing, inlets and / or outlets may be selected to minimise the creation or maintenance of bubbles in the hydraulic fluid. The shape of the tubing, inlet and / or outlet may be selected from the group comprising circular, rectangular, trapezoidal or spiral.

[0031] The at least one filter may comprise a filter material. The filter material may be selected from the group comprising fibers, paper, cellulose, synthetic fiber, mesh, metal mesh, carbon, activated carbon, a water absorption material, sodium acrylate and an additive adding material. The additive adding material may increase or decrease the density, weight and / or viscosity of the fluid. The additive adding material may release one or more additives to restore the concentration of the additive in the hydraulic fluid. The filter may be configured to dewater and / or degas the hydraulic fluid.

[0032] The two or more vessels may be storage vessels. The two or more vessels may be treatment vessels. The two or more vessels may be configured to store and / or treat hydraulic fluid. The hydraulic fluid may be a petroleum- based hydraulic fluid. The hydraulic fluid may be a hydraulic oil. The hydraulic fluid may be a synthetic hydraulic fluid. Each of the two or more vessels may be separate vessels or compartments. Each of the two or more vessels may be separate tanks. The two or vessels may be part of a single tank. Each of the two or vessels may be separate vessels or compartments in a single tank.

[0033] The valve system may comprise two or more filters. The valve system may be configured to pass hydraulic fluid through the two or more filters. The valve system may be configured to pass hydraulic fluid through the two or more filters sequentially. The filter material of the two or more filters may be the same. The filter material of the two or more filters may be different.

[0034] A first filter may comprise a water absorption material to remove water from the hydraulic fluid. A second or further filter may comprise cellulose to filter the dewatered hydraulic fluid. A second or further filter may be configured to prevent or mitigate an upstream or previous filter being overwhelmed, blocked and / or saturated. Each of the at least one filter may have a different micron rating. The two or more filters may each have a different micron rating. The micron rating may be selected from the range of 10nm to 100pm. The micron rating may be selected from the range of 100nm to 25pm.

[0035] The control unit may be configured to switch flow from one filter to another filter. The control unit may be configured to select flow through a particular filter depending on sensor data. The control unit may be configured to redirect flow from a first filter to a second filter based on measured sensor data. The control unit may be configured to select flow through a particular filter depending on particle count measurement. The control unit may be configured to redirect flow from a first filter to a second or further filter based on measured particle count data.

[0036] The control unit may be configured to redirect flow from a first flow cycle where hydraulic fluid is transferred between the two or more vessels through a high micron filter to a second flow cycle where hydraulic fluid is transferred between the two or more vessels through a low micron filter. The control unit may be configured to redirect flow from the first flow cycle to the second flow cycle based on measured particle count data.

[0037] The system may be configured to cycle hydraulic fluid back and forth between the two or more vessels through a first filter until a first desired level of cleanliness or purity of the hydraulic fluid has been reached. The system may be configured to cycle hydraulic fluid back and forth between the two or more vessels through a second filter until a second desired level of cleanliness or purity of the hydraulic fluid has been reached. The system may be configured to cycle hydraulic fluid back and forth between the two or more vessels through a third or further filter until a third or further desired level of cleanliness or purity of the hydraulic fluid has been reached.

[0038] The system may be configured for iterative filtration of hydraulic fluid back and forth between the two or more vessels through at least one filter.

[0039] The system may be configured to process 100 litres of hydraulic fluid to an ISO 4406 reading of at least 0 / 0 / 0 within 72 hours. The system may be configured to process hydraulic fluid to an ISO 4406 reading of 0 / 0 / 0. The hydraulic fluid filtration system may be mounted on or in a housing or frame. The two or more tanks may be made of plastic or metal. The floor of the two or more tanks may be sloped or may comprise a channel. The sloped floor or channel may be configured to drain as much contaminant from the tank at the end of each cycle. The geometry of the two or more tanks may be configured to redirect contaminants to move towards the tank outlet. The tank outlet may be designed to have no traps or crevices.

[0040] The system may comprise a disposal tank to deposit accumulated foreign particulate material and / or debris separated from the hydraulic fluid.

[0041] According to a second aspect of the invention, there is provided a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; a valve system; wherein the valve system is operable to control an alternating transfer of hydraulic oil between the two or more oil storage vessels through at least one filter.

[0042] The system may comprise a control unit. The control unit may be configured to control the actuation of at least one valve in the valve system.

[0043] The control unit may be configured to switch flow from one filter to another filter. The control unit may be configured to select flow through a particular filter depending on sensor data. The control unit may be configured to redirect flow from a first filter to a second filter based on measured sensor data. The control unit may be configured to select flow through a particular filter depending on water content, particle count measurement or other sensor measurements. The control unit may be configured to redirect flow from a first filter to a second or further filter based on water content, measured particle count data or other sensor measurement data.

[0044] The control unit may be configured to change flow direction of hydraulic fluid between the two or more vessels. The control unit may be configured to change flow of hydraulic fluid between the two or more vessels based on sensor data. The control unit may be configured to change flow of hydraulic fluid between the two or more vessels based on particle count data. The control unit may be configured to redirect flow from a first flow cycle where hydraulic fluid is transferred between the two or more vessels through a high micron filter to a second flow cycle where hydraulic fluid is transferred between the two or more vessels through a low micron filter (lower than the first cycle filter). The control unit may be configured to redirect flow from the first flow cycle to the second flow cycle based on measured particle count data.

[0045] Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa.

[0046] According to a third aspect of the invention, there is provided a method of removing contaminants from hydraulic fluid comprising: transferring the hydraulic fluid back and forth between two or more vessels through at least one filter.

[0047] Embodiments of the third aspect of the invention may include one or more features of the first aspect or second aspects of the invention or their embodiments, or vice versa.

[0048] According to a fourth aspect of the invention, there is provided a method of removing contaminants from hydraulic fluid comprising: providing a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; a valve system; transferring the hydraulic fluid back and forth between the two or more vessels through the at least one filter.

[0049] The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a first filter until a first desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a second filter until a second desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a third or further filter until a third or further desired level of cleanliness or purity of the hydraulic fluid has been reached. The number of times the hydraulic fluid is transferred back and forth between the two or more vessels through a filter depends on the level of contamination of the hydraulic fluid and / or the desired level of cleanliness or purity of the hydraulic fluid to be reached.

[0050] The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter two or more times. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter at least five times. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter at least ten times. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter at least twenty times. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter between twenty and one hundred times. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter between one hundred times and two hundred times. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter between one hundred times and five hundred times. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a filter between one hundred times and one thousand times.

[0051] The method may comprise removing contaminants from a vessel by contacting a volume of filtered hydraulic fluid with the contaminants and diffusing particles of the contaminants into the filtered hydraulic fluid. The method may comprise removing contaminants from a vessel by contacting transferred hydraulic fluid with the contaminants and diffusing particles of the contaminants into the transferred hydraulic fluid. The method may comprise removing fluid comprising contaminants from a vessel by contacting a volume of filtered hydraulic fluid with the fluid comprising contaminants and diffusing particles of the contaminants from the fluid comprising contaminants into the filtered hydraulic fluid. The method may comprise removing impurities from a vessel by contacting a volume of filtered hydraulic fluid with the contaminated fluid and diffusing particles of impurities from the contaminated fluid into the filtered hydraulic fluid.

[0052] The method may comprise diffusing contaminants present in at least one of the vessels into the transferred hydraulic fluid. The method may comprise diffusing contaminants present in each vessel into the transferred hydraulic fluid. The method may comprise diffusing contaminants present in a first vessel into the transferred hydraulic fluid before it is transferred to the second vessel through the at least one filter. The method may comprise diffusing particles of impurities present in the vessel into the transferred hydraulic fluid. The method may comprise diffusing contaminants from each of the two or more vessels into the hydraulic fluid each time the hydraulic fluid is transferred back and forth between the two or more vessels through the at least one filter.

[0053] The method may comprise measuring and / or monitoring at least one characteristic or parameter of the hydraulic fluid. The at least one characteristic or parameter of the hydraulic fluid may be selected from the group comprising temperature, pressure, viscosity, particle count, gas content, air content, water content and / or humidity.

[0054] The method may comprise measuring a particle count of at least a sample of the hydraulic fluid. The method may comprise measuring a particle count of at least a sample of the hydraulic fluid each time it passes through a filter.

[0055] The method may comprise switching flow from one filter to another filter. The method may comprise selecting flow through a particular filter depending on sensor data. The method may comprise redirecting flow from a first filter to a second filter based on measured sensor data. The method may comprise selecting flow through a particular filter depending on measured particle count. The method may comprise redirecting flow from a first filter to a second or further filter based on measured particle count data.

[0056] The method may comprise redirecting flow from a first flow cycle where hydraulic fluid is transferred between the two or more vessels through a high micron filter to a second flow cycle where hydraulic fluid is transferred between the two or more vessels through the low micron filter. The method may comprise redirecting flow from the first flow cycle to the second flow cycle based on measured particle count data.

[0057] The method may comprise dewatering and / or degassing the hydraulic fluid before measuring a particle count.

[0058] The contaminants may be selected from the group comprising solid particles, metal particulates, impurities, wear particles, fibres, free radicals, solutes, chemicals, water, gas and / or air. The hydraulic fluid may be new hydraulic fluid. By “new hydraulic fluid” it is meant hydraulic fluid which has not been used in a hydraulic system. The method may be used to remove contaminants and / or increase the purity of new hydraulic fluid before it is first introduced and used in a hydraulic system.

[0059] The hydraulic fluid may be recycled hydraulic fluid or recovered hydraulic fluid previously used in a hydraulic system. The filtration system may be an online system where the hydraulic fluid is temporarily extracted from and / or is circulating in a hydraulic system. The filtration system may be an offline system where the hydraulic fluid is extracted from and / or is removed from the hydraulic system before filtration.

[0060] Embodiments of the fourth aspect of the invention may include one or more features of the first to third aspects of the invention or their embodiments, or vice versa.

[0061] According to a fifth aspect of the invention, there is provided a method of removing contaminants from new hydraulic fluid prior to introducing the hydraulic fluid into a hydraulic system comprising: providing a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; a valve system; transferring the hydraulic fluid back and forth between the two or more vessels through the at least one filter.

[0062] The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a first filter until a first desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a second filter until a second desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a third or further filter until a third or further desired level of cleanliness or purity of the hydraulic fluid has been reached.

[0063] The method may comprise measuring and / or monitoring at least one characteristic or parameter of the hydraulic fluid. The at least one characteristic or parameter of the hydraulic fluid may be selected from the group comprising temperature, pressure, viscosity, particle count, gas content, air content, water content and / or humidity.

[0064] Embodiments of the fifth aspect of the invention may include one or more features of the first to fourth aspects of the invention or their embodiments, or vice versa.

[0065] According to a sixth aspect of the invention, there is provided a method of removing contaminants from hydraulic fluid from a hydraulic system comprising: providing a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; a valve system; transferring the hydraulic fluid back and forth between the two or more vessels through the at least one filter.

[0066] Embodiments of the sixth aspect of the invention may include one or more features of the first to fifth aspects of the invention or their embodiments, or vice versa.

[0067] According to a seventh aspect of the invention, there is provided a method of removing contaminants from hydraulic fluid in a hydraulic system of a piece of equipment comprising: providing a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; a valve system; connecting the hydraulic fluid filtration system to the hydraulic system; transferring the hydraulic fluid back and forth between the two or more vessels through the at least one filter.

[0068] The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a first filter until a first desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a second filter until a second desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a third or further filter until a third or further desired level of cleanliness or purity of the hydraulic fluid has been reached.

[0069] The method may comprise measuring and / or monitoring at least one characteristic or parameter of the hydraulic fluid. The at least one characteristic or parameter of the hydraulic fluid may be selected from the group comprising temperature, pressure, viscosity, particle count, particle content, gas content, air content, water content and / or humidity. The particle content may be selected from the group comprising metal particles, non-metal particles, minerals, fibres and / or free radicals.

[0070] Embodiments of the seventh aspect of the invention may include one or more features of the first to sixth aspects of the invention or their embodiments, or vice versa.

[0071] According to an eighth aspect of the invention, there is provided a method of removing contaminants from hydraulic fluid from a hydraulic system comprising: providing a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; a valve system; extracting hydraulic fluid from the hydraulic system; transferring the hydraulic fluid back and forth between the two or more vessels through the at least one filter.

[0072] The method may comprise reintroducing treated hydraulic fluid into the hydraulic system.

[0073] Embodiments of the eighth aspect of the invention may include one or more features of the first to seventh aspects of the invention or their embodiments, or vice versa.

[0074] According to a ninth aspect of the invention, there is provided a method of recycling hydraulic fluid comprising: providing a hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; transferring the hydraulic fluid back and forth between the two or more vessels through the at least one filter to remove contaminants from hydraulic fluid. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a first filter until a first desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a second filter until a second desired level of cleanliness or purity of the hydraulic fluid has been reached. The method may comprise transferring the hydraulic fluid back and forth between the two or more vessels through a third or further filter until a third or further desired level of cleanliness or purity of the hydraulic fluid has been reached.

[0075] The method may comprise measuring and / or monitoring at least one characteristic or parameter of the hydraulic fluid. The method may comprise measuring and / or monitoring at least one characteristic or parameter of the hydraulic fluid each time the hydraulic fluid passes through the filter. The at least one characteristic or parameter of the hydraulic fluid may be selected from the group comprising temperature, pressure, viscosity, particle count, gas content, air content, water content and / or humidity.

[0076] Embodiments of the ninth aspect of the invention may include one or more features of the first to eighth aspects of the invention or their embodiments, or vice versa.

[0077] Brief Description of the Drawings

[0078] There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

[0079] Figure 1 is a schematic view of a hydraulic fluid filtration system in accordance with a first embodiment of the invention;

[0080] Figure 2 is a flow chart of a filtration operation using the hydraulic fluid filtration system of Figure 1 ;

[0081] Figure 3A to 3C are a perspective, exploded and partially cross-sectional views of a hydraulic fluid filtration system in accordance with an embodiment of the invention;

[0082] Figure 4 is a schematic view of the flow circuit of the hydraulic fluid filtration system of Figure 3A; Figure 5 is a schematic view of the flow circuit of the hydraulic fluid filtration system of Figure 3A showing a back flush fluid circuit; and

[0083] Figures 6A to 6C are particle size count plots over time for the three different micron levels.

[0084] Detailed Description

[0085] Figure 1 is a flow circuit of a filtration system 10. The system comprises two tanks 12a 12b which store hydraulic fluid. Each of the tanks 12a, 12b are fluidly connected to a filter system 14 via a valve system 16. In this example the tanks are made of steel and each has a storage capacity of 205 litres. However, the tanks may be made of other materials and may have a range of sizes and storage capacities.

[0086] The filter system 14 in this example comprises five filters 14a, 14b, 14c, 14d and 14e. The filters may each have a different micron rating. In this example filter 14a is a 10pm filter; filter 14b is a 3pm filter, filter 14c is a 1pm filter; filter 14d is a 100nm filter and filter 14e is a 10pm filter. The filters in this example are made of cellulose. However, one or more filters may be made of an alternative filter material.

[0087] The valve system 16 comprises four filter valves 18a, 18b, 18c and 18d. The filter valves are configured to control flow into and out from each filter. The valve system 16 optionally has a pressure reducing valve 20 to regulate the pressure in the flow circuit to prevent high pressure build up through the filters.

[0088] The valve system 16 comprises an outflow valve 22 connected to outlet 26a on tank 12a and outlet 26b on tank 12b. The valve system 16 also comprises an inflow valve 24 connected to inlet 28a on tank 12a and inlet 28b on tank 12b. The system comprises a detection system 30 to monitor contamination in the hydraulic fluid which in this example is a particle counter 32.

[0089] Figure 2 is a flow chart 80 describing the operation of the filtration method using the system 10. As shown in Figure 1 and step 82 of Figure 2 the hydraulic fluid to be treated is stored in tank 12a. Valve 22 is open to a pathway between flow path 40 and 42. A pump 70 connected to flow path 42 draws hydraulic fluid from tank outlet 26a on vessel 12a to flow path 44 to the filter valves. First filter valve 18a is actuated to open a path to first filter 14a. The hydraulic fluid passes through a 10pm filter 14a and large contaminates are removed from the fluid. The filtered fluid passes from the filter 14a though flow path 46. To monitor the purity of the hydraulic fluid, valve 60 provides a small amount of pressure resistance to provide flow through flow path 48 to particle counter 32 as well as though flow paths 50 and 52 to the inflow valve 24. Valve 24 is actuated to open a flow path to the tank inlet 28b and the treated fluid enters tank 12b. In this example purity sampling is performed continuously.

[0090] The fluid in tank 12a continues to pass through the filter system to tank 12b until a low level indicator in tank 12a detects a low fluid level. The indicator provides a signal to stop the pump. This prevents air being drawn into the filter system. In this example tank 12b has a high level indicator to prevent overflow. The high level indicator may detect a high induced oil fill level and switch off the pump drawing the fluid in. This high level indicator may also act as a switch off in the event that the fluids temperature has led to expansion and over spill.

[0091] When the low level indicator in tank 12a detects a low fluid level the pump 70 is stopped and the outflow valve 22 is actuated to then open a pathway between flow path 41 connected to the tank 12b outlet and flow path 42. The pump 70 connected to flow path 42 gradually draws hydraulic fluid from tank 12b to flow path 44 to the filter valves. In a first filtration operation the first filter valve 18a is actuated to open a path to first filter 14a. The hydraulic fluid passes through 10pm filter and large contaminates are removed from the fluid. The filtered fluid passes from the filter 14a though flow path 46. When a purity sampling is required a valve in location 60 can be closed and the treated hydraulic fluid passes through flow path 48 to particle counter 32 and though flow paths 50 and 52 to the valve 24. Valve 24 is actuated to open a flow path to the tank inlet 28a and the treated fluid enters tank 12a. The fluid in tank 12b continues to pass through the filter system to tank 12a until a low level indicator in tank 12b detects a low fluid level to prevent air being drawn into the filter system. Similar to tank 12b, tank 12a also has a high level indicator to prevent overflow.

[0092] The above sequence of passing the hydraulic fluid back and forth between tanks 12a and 12b through the first 10pm filter 14a is continued until the reduction in the level of contaminants measured by the particle counter drops to a desired preset target level. This indicates that the majority of contaminants in fluid are less than 10pm and are not being removed by the 10pm filter 14a.

[0093] In this example by passing the hydraulic fluid a first pass through a 10 micron filter from the first tank to the second tank, 99.9% of all particles greater than 10 micron are removed from the fluid. By returning that fluid back through the filter from the second tank to the first tank the fluid is further cleaned.

[0094] The cleaner fluid returning into the first tank will be exposed to a small amount of contaminated fluid containing foreign particles on the walls and base of the first tank. The particles are drawn to the cleaner fluid entering the first tank by diffusion. There is no need to physical sweep the tank walls remove the contaminated fluid. The contaminated fluid migrates into the clean fluid by diffusion of small scale matter into a very pure fluid. Passing the fluid again from the first tank to the second tank 99.9% of the remaining 0.01% particles of the fluid is further removed. By repeating this back and forth filtration cycle multiple times e.g. 50 cycles, a high purity / cleanliness of fluid may be obtained.

[0095] At this stage shown as step 84 of Figure 2, the sequence of passing the hydraulic fluid back and forth between tanks 12a and 12b is adjusted by actuating the second filter valve 18b to open a path to the second filter 14b and passing fluid through the 3pm second filter 14b instead of the first filter 14a. The hydraulic fluid is passed back and forth between tanks 12a and 12b through the second 3pm filter 14b until the reduction in the level of contaminants measured by the particle counter drops to a preset level. This indicates that the majority of contaminants in the fluid are less than 3pm and are not being removed by the 3pm filter 14b.

[0096] At this third stage shown as step 86 of Figure 2 the sequence of passing the hydraulic fluid back and forth between tanks 12a and 12b is adjusted by actuating the third filter valve 18c to open a path to the third filter 14c and passing fluid through the 1pm third filter 14c instead of the second filter 14b. The hydraulic fluid is passed back and forth between tanks 12a and 12b through the third 1pm filter 14c until the reduction in the level of contaminants measured by the particle counter drops to a preset target level. This indicates that the majority of contaminants in fluid are less than 1 pm and are not being removed by the 1 pm filter 14c. At this fourth stage shown as step 88 of Figure 2 the sequence of passing the hydraulic fluid back and forth between tanks 12a and 12b is adjusted by actuating the fourth filter valve 18d to open a path to the fourth filter 14d and passing fluid through the 100nm filter 14d instead of the third filter 14c. The hydraulic fluid is passed back and forth between tanks 12a and 12b through the fourth 100nm filter 14d until the reduction in the level of contaminants measured by the particle counter drops to a preset target level. This indicates that the majority of contaminants in fluid are less than 100nm and are not being removed by the 100nm filter 14d.

[0097] As the 100nm filter is fine and delicate, over time the 100nm filter 14d may degrade and disintegrate. This can introduce filter fibre particles and debris into the fluid. Optionally a fifth filter 14e is provided with a higher micron rating of 10 pm and is configured to capture and remove filter fibre particles should filter 14d disintegrate, shown as step 90 of Figure 2. The hydraulic fluid is passed back and forth between tanks 12a and 12b through the fifth 10 pm filter 14e.

[0098] Optionally a control system may control the selective switching between the filters based on the particle counter data. The system may be an automated system.

[0099] Although the system above describes the sequentially filtration through all five filters it will be appreciated the system may comprise less than or more than five filters. It will be appreciated that the system may comprise filter micron levels different to the above example. It will also be appreciated that the method may not require that the fluid is passed through all filters. The filtration method may be conducted until a desired fluid cleanliness or purity is reached.

[0100] The system described in Figures 1 and 2 can be used to sequentially filter used hydraulic fluid to remove contaminants. Additional or alternatively the system can be used to remove contaminants from new hydraulic fluid before it is first introduced into a hydraulic system.

[0101] ISO 4406 is the standard which specifies the code to be used in defining the quantity of solid particles in a fluid used in a given hydraulic fluid power system. According to this standard, a code number is assigned to particle count values derived at three different micron levels: 4 microns, 6 microns and 14 microns. The ISO code is assigned based upon Table 1. Under ISO 4406 there is a typical particle count scheme which divided the count of particles per millilitre. Therefore a particle count of 15 / 13 / 11 means between 160 and 320 particles at 4 microns; 40 to 80 particles at 6 microns and between 10 and 20 particles at 14 microns.

[0102] Table 1 is an ISO 4406 particle concentration table in particles per milli itre.

[0103] New hydraulic fluid is typically found to have an ISO Code of between 18 / 17 / 16 and 14 / 13 / 11 although this can vary significantly. An ISO Code of 11 means that per ml of fluid there are between 10 and 20 particles of 14pm size. These particles are a size which lies between 500 and 400 grit size as typically found in industrial grinding paste. As the hydraulic fluid will pass through a hydraulic system from high to low pressure and back again thousands of times, these particles have the potential to cause great damage. However, by processing new hydraulic fluid through the system 10 as described above in relation to Figure 1 and 2 before it is used in a hydraulic system, particles can be removed from the hydraulic system which may mitigate wear to the hydraulic system.

[0104] Figures 3A to 3C and 4 show a filtration system 100. The system 100 is similar to the filtration system 10 described in relation to Figures 1 and 2 and will be understood from the description of Figures 1 and 2. However the system is configured to remove water from hydraulic fluid. The system comprises two tanks 112a and 112b which store hydraulic fluid. Each of the tanks 112a, 112b are fluidly connected to a filter system 114 via a valve system 116. The tanks are made of steel and each has a storage capacity of 205 litres. However, the tanks may be made of other materials and may have a range of sizes and storage capacities. Figure 3C shows a cross sectional view of tank 112b, the features of the tanks 112a and 112b in this example are the same. In Figure 3C the connection tubes have been removed for clarity. Each tank has an inlet 128 and an outlet 126. The tanks are arranged such that fluid returning to each tank via the inlet 128 travels down the inner sides or walls of each tanks which cleans the walls removing any collected debris or dirt. The tanks have braces and baffles 115 which provide the tanks with structural support. The floor 117 of the tanks in this example are sloped. The sloped floor 117 is configured to drain as much contaminant from the tank at the end of each cycle. The sloped floor is designed naturally to provide a self-purging / draining bottom / floor. Each tank has an upper fluid level sensor 119a to prevent overfilling and a lower fluid level sensor 119b to prevent air being drawn into the filtration system.

[0105] In this example the filter system 114 comprises four filters 114a, 114b, 114c and 114d. The filters have a different micron rating. Filter 114a is a 10pm filter; filter 114b is a 3pm filter, filter 114c is a 1pm filter; and filter 114d is a 100nm filter. The filters in this example are made of different filter material. Filters 114a is made of a water absorption material such as sodium acrylate. Filters 114b, 114c and 114d are made of cellulose.

[0106] In this example an electromagnet is located in the housing of filter 114b to remove and collect ferrous materials from the hydraulic fluid. Alternatively the electromagnet may be incorporated into a flow path. The actuation of the electromagnet may be controlled to allow selective collection and / or controlled release of the collected ferrous materials to a particular filter at a preferred time. This mitigates the magnet becoming overwhelmed or blocked due to collected ferrous materials.

[0107] The system also comprises a control unit 130, particle counter 132. Optionally the system may comprise heating devices, cooling devices and / or acoustic transducers to assist in removal of air and water from the hydraulic fluid (not shown).

[0108] As best shown in Figure 4, in use, hydraulic fluid to be treated is stored in a first tank such as tank 112a. The control unit 130 actuates a valve 122 to open a pathway between flow path 140 and 142. A pump 170 connected to flow path 142 draws hydraulic fluid from tank 112a to flow path 144 to the filter valves.

[0109] First filter valve 118a is actuated to open a flow path to first filter 114a. The hydraulic fluid passes through the 10pm filter where water is absorbed by the water absorbing material and large contaminates (10pm or more) are removed from the fluid. The filtered fluid passes from the filter 114a though flow path 146. When a purity sampling is required valve 160 is closed (fully or partially) and the treated hydraulic fluid passes through flow path 148 to particle counter 132 and though flow paths 150 and 152 to the inflow valve 124. Valve 124 is actuated to open a flow path to the tank inlet 128b and the treated fluid enters tank 112b.

[0110] The fluid in tank 112a continues to pass through the filter system to tank 112b until a low level indicator in tank 112a detects a low fluid level. This prevents air being drawn into the filter system. In this example tank 112b has a high level indicator to prevent overflow. The high level indicator may detect a high induced oil fill level and switch off the pump drawing the fluid in. This high level indicator may also act as a switch off in the event that the fluids temperature has led to expansion and over spill.

[0111] When the low level indicator in tank 112a detects a low fluid level the pump 170 is stopped and the outflow valve 122 is actuated to open a pathway between flow path 141 connected to the tank 112b outlet and flow path 142. The pump 170 connected to flow path 142 draws hydraulic fluid from tank 112b to flow path 144 to the filter valves. In a first filtration operation the first filter valve 118a is actuated to open a path to first filter 114a. The hydraulic fluid pass through 10pm filter where water is absorbed by the water absorbing material and large contaminates missed in the first pass (10pm or more) are removed from the fluid. The filtered fluid passes from the filter 114a though flow path 146. When a purity sampling is required valve 160 is closed (fully or partially) and the treated hydraulic fluid passes through flow path 148 to particle counter 132 and though flow paths 150 and 152 to the valve 124. Valve 124 is actuated to open a flow path to the tank inlet 128a and the treated fluid enters tank 112a.

[0112] The above sequence of passing the hydraulic fluid back and forth between tanks 112a and 112b may be repeated multiple times through the water absorbing 10pm filter 114a until the reduction in the level of contaminants measured by a humidity sensor and a particle counter drops to a preset target level. This indicates that the water has been removed from the fluid or reduced to a desired level and that the majority of contaminants in fluid are less than 10pm.

[0113] At this stage, the control unit adjusts the filtration sequence by actuating the second filter valve 118b to open a path to the second filter 114b and passing fluid through the second filter 114b which is a 3pm cellulose filter instead of the first filter 114a. As the water content of the hydraulic has been removed or significantly reduced the risk of damage to the cellulose by water is mitigated. The hydraulic fluid is passed back and forth between tanks 112a and 112b through the second 3pm filter 114b multiple times until the reduction in the level of contaminants measured by the particle counter drops to a preset level. This indicates that the majority of contaminants in fluid are less than 3pm and are not being removed by the 3pm filter 114b.

[0114] At this third stage the control unit adjusts the filtration sequence by actuating the third filter valve 118c to open a path to the third filter 114c and passing fluid through the 1 pm third filter 114c instead of the second filter 114b. The hydraulic fluid is passed back and forth between tanks 112a and 112b through the third 3pm filter 114c multiple times until the reduction in the level of contaminants measured by the particle counter drops to a preset target level. This indicates that the majority of contaminants in fluid are less than 1 pm and are not being removed by the 3pm filter 14c.

[0115] At this fourth stage the control unit adjusts the filtration sequence by actuating the fourth filter valve 118d to open a path to the fourth filter 114d and passing fluid through the 100nm filter 114d instead of the third filter 114c. The hydraulic fluid is passed back and forth between tanks 112a and 112b through the fourth 100nm filter 14d multiple times until the reduction in the level of contaminants measured by the particle counter drops to a preset target level. This indicates that the majority of contaminants in fluid are less than 100nm.

[0116] The presence of air bubbles in hydraulic fluid may affect the accuracy of the particle counter reading. Figure 6A to 6C show particle size count plots over time for the three different micron levels. Figure 6A is the isolated particle count data for 4pm plot over time. Figure 6B is the isolated particle count data for 6pm plot over time. Figure 6C is the isolated particle count data for 14pm plot over time. Air bubbles may cast a shadow which can be mis-interpreted by the particle counter as ‘particles. In each of the plots the ‘real’ particles are shown by the data points which trend towards the base line. As shown in Figures 6A to 6C at 6pm and in particular 4pm, air bubbles do not float out of the fluid easily. The mid plot ‘cloud’ of points are actually for the most part air bubbles, these effect the detector in the laser and cast a shadow on the sensor, so are counted as ‘particles. Figure 6C shows that at 14pm, the bubble particle count reduces with time more readily.

[0117] The system may comprise apparatus to assist in the removal of air from the hydraulic fluid. In one example an ultrasonic device such as an ultrasonic transducer may be integrated into the system to remove dissolved gasses and / or entrained air bubbles from the hydraulic fluid. The ultrasonic device may create ultrasonic cavitation transferring any air microbubbles into large bubbles with burst at the surface of the hydraulic fluid. In another example vortex separators may be used to remove air from the hydraulic fluid.

[0118] Additionally or alternatively the geometry of the system may be designed to assist in air rising out from the hydraulic fluid. The diameter of tubing, inlets and / or outlets may be configured to minimise bubble flow effect in hydraulic fluid. The shape of the tubing, inlets and / or outlets may be selected to minimise bubble flow effect in hydraulic fluid. The shape of the tubing, inlet and / or outlet may be selected from the group comprising circular, rectangular, trapezoidal or spiral.

[0119] The tank inlets may be arranged such that fluid returning to each tank travels down the inner sides or walls of each tanks which cleans the walls removing any debris or dirt. The floor of the two or more tanks may be sloped or may comprise a channel. The sloped floor or channel may be configured to drain as much contaminant from the tank at the end of each cycle. The geometry of the two or more tanks may be configured to redirect contaminants to move towards the tank outlet.

[0120] Additionally or alternatively to particle counter sensors the system may comprise other sensors or instruments selected from the group of humidity sensors, light irradiation, capacitance, flow meters, density sensors, viscosity sensors, pressure sensor, temperature sensor, liquid level indicators, ultrasonic sensors, magnetostrictive sensors, level probes, rod sensors, limit sensors, fluid level switches, fill level switches and / or float switches. As shown in Figure 5 the system including tanks and filters may be periodically flushed to removed collected contaminants from a filtration operation. After a filtration operation a quantity of clean hydraulic fluid is introduced into tank 112a, the control unit actuates the pump 170 to pump in a reverse direction shown as arrows “C” in Figure 5. The flow continues along flow path 152, into the first filter 114a back flushing the filter to remove collected filtrate. The flushing fluid passes along flow path 144 to flow path 180 and is collected in waste tank 182. The process may be repeated for the second tank 112b. The control unit sequentially opens pathways to the each of the filters to flush out any built up contaminants in the each of the filters.

[0121] Although the above example describes the use of a filter material comprising a water absorption material to dewater the hydraulic fluid it will be appreciated that additionally or alternatively the system may include other dewatering means including separation by gravity, heating, cooling, positive pressure dehydrators, centrifugal segregation or vacuum dehydrators.

[0122] It will be appreciated that the above system may be a closed or offline system where a measured batch of hydraulic fluid is introduced into the system, treated and discharged once a desired improved treated condition has been reached. It will also be appreciated that the above system may be an open or online system where the system is in fluid communication with a hydraulic system of a piece of equipment and hydraulic fluid is drawn from the hydraulic system in controlled measured amounts, treated and discharged back into the hydraulic system once a desired improved treated condition has been reached.

[0123] Aspects of the invention may provide a hydraulic fluid filtration system capable of circulating hydraulic fluid through a filter passing back and forth between two vessels. Each time the fluid passes from one vessel to the other vessel the fluid is progressively cleaned. By repeatedly passing the fluid back and forth through the filter a high level of cleanliness or purity of the hydraulic fluid may be obtained.

[0124] The inventors have found that providing two vessels and repeatedly passing hydraulic fluid back and forth through a filter system between the vessels a high level of cleanliness or purity of the hydraulic fluid may be obtained without the need for a large number of filters, tanks or a large apparatus footprint . The inventors have also found that the vessels or equipment does not require cleaning between filtration cycles. The inventors have found that after a first filtration cycle although the filtered fluid is returned to the contaminated first vessel, which may contain fluid with impurities, by repeatedly passing fluid back and forth though the filter system the impurities are gradually removed from both vessels and the hydraulic fluid over time.

[0125] Throughout the specification, unless the context demands otherwise, the terms 'comprise' or 'include', or variations such as 'comprises' or 'comprising', 'includes' or 'including' will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. Furthermore, relative terms such as”, “inlet” .“outlet” and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations. The term “outlet” shall be construed as being an opening which, dependent on the direction of the movement of fluid may also serve as an “entry”, and vice versa.

[0126] The invention provides a hydraulic fluid filtration system and method of use. The system comprises two or more vessels, a filter system comprising at least one filter arranged between the two or more vessels and a valve system. The valve system is operable transfer hydraulic fluid between the two or more vessels through the at least one filter. The present invention may provide a robust, reliable and compact hydraulic fluid filtration apparatus and method of use capable of removing contaminants from hydraulic oil before, during and / or after it is used in a hydraulic system of a piece of equipment.

[0127] An embodiment of the invention may provide a filtration system comprising multiple filters wherein should one filter be compromised or degrade the fluid passes through another filter and the contaminants and / or degraded filter components are captured by the filter rather than passing into the hydraulic system of a piece of equipment.

[0128] An embodiment of the invention may provide a hydraulic fluid filtration system configured to be integrated in or connected to a hydraulic system of a piece of equipment. The hydraulic fluid filtration system may filter hydraulic fluid online or offline.

[0129] The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention herein intended.

Claims

Claims1. A hydraulic fluid filtration system comprising: two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; and a valve system; wherein the valve system is operable to transfer hydraulic fluid back and forth between the two or more vessels through the at least one filter.

2. The system according to claim 1 wherein the valve system is configured to cycle hydraulic fluid back and forth between the two or more vessels through the at least one filter until a desired cleanliness level of the hydraulic fluid has been reached.

3. The system according to any of claim 1 or claim 2 comprises a control unit configured to control the actuation of one or more valves in the valve system.

4. The system according to any preceding claim wherein the at least one filter has a micron rating selected from the range of 10nm to 100pm.

5. The system according to any preceding claim comprises at least one pump, wherein the at least one pump is a reversible pump.

6. The system according to any preceding claim comprises at least one heating device configured to increase the temperature of the hydraulic fluid to a desired temperature to reduce the fluid viscosity and / or assist in the removal of water and / or air from the hydraulic fluid.

7. The system according to any preceding claim comprises at least one cooling device configured to reduce the temperature of the hydraulic fluid to a desired temperature to reduce the fluid viscosity and / or assist in the removal of water and / or air from the hydraulic fluid.

8. The system according to any preceding claim wherein the at least one filter comprises a filter housing wherein the filter housing comprises at least onedevice selected from the group of a magnet, electromagnet, cooling device and / or heating device.

9. The system according to any preceding claim wherein the hydraulic fluid filtration system comprises at least one sensor selected from the group including particle counter, humidity sensor, light sensor, optical sensor, capacitance sensor, flow meter, density sensor, viscosity sensor, pressure sensor, temperature sensor, liquid level indicators, ultrasonic sensor, magnetostrictive sensor, level probes, rod sensor, limit sensor, level and fill level switches, spectroscopy sensor, optical spectrometry sensor and / or float switches.

10. The system according to any preceding claim comprises a degassing device selected from the group comprising vortex separator, cyclone separator, ultrasonic transducer, vacuum degasser, fluid agitator, deaerator and / or centrifugal deaerator.11 . The system according to any preceding claim wherein the at least one filter comprises a filter material selected from the group comprising fibers, paper, cellulose, synthetic fiber, mesh, metal mesh, carbon, activated carbon, a water absorption material, sodium acrylate and an additive adding material.

12. The system according to any preceding claim wherein the valve system comprises two or more filters.

13. The system according to claim 12 wherein valve system is configured to selectively pass hydraulic fluid through the two or more filters sequentially.

14. The system according to claim 12 or claim 13 wherein the two or more filters each have a different micron rating selected from the range of 10nm to 100pm.

15. The system according to any preceding claim wherein the valve system is configured to select flow through a particular filter depending on sensor data.

16. A method of removing contaminants from hydraulic fluid comprising: providing a hydraulic fluid filtration system comprising:two or more vessels; a filter system comprising at least one filter arranged between the two or more vessels; a valve system; transferring the hydraulic fluid back and forth between the two or more vessels through the at least one filter.

17. The method according to claim 16 comprising transferring the hydraulic fluid back and forth between the two or more vessels through a first filter until a first desired level of cleanliness or purity of the hydraulic fluid has been reached.

18. The method according to claim 16 or claim 17 comprising transferring the hydraulic fluid back and forth between the two or more vessels through a second filter until a second desired level of cleanliness or purity of the hydraulic fluid has been reached.

19. The method according to any of claims 16 to 18 comprising transferring the hydraulic fluid back and forth between the two or more vessels through a third or further filter until a third or further desired level of cleanliness or purity of the hydraulic fluid has been reached.

20. The method according to any of claims 16 to 19 comprising measuring and / or monitoring at least one characteristic or parameter of the hydraulic fluid wherein the at least one characteristic or parameter of the hydraulic fluid is selected from the group comprising temperature, pressure, viscosity, particle count, gas content, air content, water content and / or humidity.

21. The method according to any of claims 16 to 20 comprising selecting flow through a particular filter depending on sensor data.

22. The method according to any of claims 16 to 21 wherein the hydraulic fluid is new hydraulic fluid wherein contaminants are removed from the hydraulic fluid before it is first introduced and used in a hydraulic system.

23. The method according to any of claims 16 to 22 wherein the hydraulic fluid is recovered hydraulic fluid previously used in a hydraulic system.

24. The method according to any of claims 16 to 23 comprising connecting the hydraulic fluid filtration system to a hydraulic system and temporarily extracting hydraulic fluid from hydraulic system and / or filtering hydraulic fluid circulating in the hydraulic system.

25. The method according to any of claims 16 to 24 comprising extracting hydraulic fluid from the hydraulic system.

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