Hydraulic pump for pumping viscous fluid from a lubricant reservoir

Abstract

The present disclosure relates to a hydraulic pump for pumping viscous fluid, such as lubricant grease, from a lubricant reservoir (3), and a grease pump system (1) for pumping lubricant grease. The present disclosure further relates to a method for reducing air locks of a hydraulic pump (1) when supplying lubricant grease from a lubricant reservoir. One embodiment relates to a hydraulic pump for pumping fluid from a lubricant reservoir (3), the hydraulic pump comprising a positive displacement rotary pump having a housing (8), a low pressure inlet (4) for connection to the lubricant reservoir (3) and a high pressure outlet (5), an external case drain port (6) arranged to drain leakage from a high pressure side of the positive displacement rotary pump (1) into the housing (8) thereof, an external case drain flow path (16, 17) connecting the external case drain port (6) and the lubricant reservoir (3), and a pressure relief valve (7) located in the external case drain flow path (16, 17), the pressure relief valve (7) being configured to open and allow fluid to flow towards the lubricant reservoir (3) upon a predefined minimum fluid pressure being exceeded by fluid in the external case drain flow path (16, 17).

Description

[0001] Hydraulic pump for pumping viscous fluid from a lubricant reservoir

[0002] The present disclosure relates to a hydraulic pump for pumping viscous fluid, such as lubricant grease, from a lubricant reservoir, for example for use in a grease pump system for pumping lubricant grease into a central lubrication system. The present disclosure further relates to a method for reducing the risk of air locks of a hydraulic pump when supplying lubricant grease from a lubricant reservoir.

[0003] Background

[0004] Highly viscous fluids such as lubricant grease or fat often contain small air bubbles incorporated in the fluid. Hence, when pumping highly viscous fluids, there is constantly a risk that larger air bubbles will be present in the pumping chamber of the positive displacement rotary pump, which may cause the pump to stall, i.e. reduce or stop the flow of fluid through the pump, because the compressible larger air bubble will hinder the pumping function of the positive displacement rotary pump, that is, the pump becomes air locked.

[0005] Air locks may also arise when the viscous fluid not itself flows and fills the suction inlet of the pump, which may cause air to be mixed into the fluid on the suction side of the pump.

[0006] One example of how to reduce air locks in a pump system is provided in WO 2021 / 105362 disclosing two serially connected positive displacement pumps where the second pump removes air bubbles introduced into the pumping chamber of the first pump. However, it doubles the cost of the pump system if two pumps are needed for a task that can be handled by a single pump.

[0007] Summary

[0008] A purpose of the present disclosure is to provide a cost efficient solution to reduce or eliminate the risk of air locks of a hydraulic pump when supplying a lubricant, in particularly lubricant grease from a lubricant reservoir, such that the hydraulic pump becomes less prone to experience the presence of air bubbles present in the pump chamber of a magnitude that causes the pump to air lock. Positive displacement rotary pumps are pumps using the actions of rotating cogs or gears to transfer fluids, rather than the backwards and forwards motion of reciprocating positive displacement pumps. The rotating element develops a liquid seal with the pump casing and creates suction at the pump inlet. Fluid, drawn into the pump, is enclosed within the teeth of its rotating cogs or gears and transferred to the discharge pump outlet. The simplest example of a positive displacement rotary pump is the gear pump. There are two basic designs of gear pump: external and internal. An external gear pump consists of two interlocking gears supported by separate shafts (one or both of these shafts may be driven). Rotation of the gears traps the fluid between the teeth moving it from the inlet, to the discharge, around the casing. No fluid is transferred back through the centre between the gears, because they are interlocked. An internal gear pump operates by same principle, but the two interlocking gears are of different sizes with one rotating inside the other. The cavities between the two gears are filled with fluid at the inlet and transported around to the discharge port, where it is expelled by the action of the smaller gear. Gear pumps are lubricated by the pumped fluid and are ideal for pumping oils and other high viscosity liquids. Two other designs similar to the gear pump are the lobe pump and vane pump. A further class of rotary pumps uses one or several, meshed screws to transfer fluid along the screw axis. Positive displacement rotary pumps are often used for pumping fluids with a certain viscosity such as oil, paints, resins or foodstuffs.

[0009] Positive displacement rotary pumps, such as an external gear pump, are suitable for pumping viscous fluids, like oil or grease. Drainage are often provided in such pumps, either internal drainage or external drainage, in order to handle leakage through clearances in the pump, typically the small clearance between the gears. An internal drainage merely recirculates the leaked fluid inside the pump, whereas the use of an external drainage requires more active handling of the leaked fluid, e.g. it can be guided to a waste reservoir or recirculated to a lubricant reservoir. However, with highly viscous fluids, like grease, there is an increase in air bubbles that are locked within the grease. This will inevitably increase the risk of air locks of the hydraulic pump. Drainage of the pump ensures that many of air bubbles are leaked out through the drainage, but with an internal drainage the air bubbles merely enter the pump again and even with an external drainage the air bubbles will just enter the system again if recirculated, and if the leaked fluid is discarded a lot of the desired fluid is wasted. Positive displacement rotary pumps are typically provided with a case drain to handle fluid that escapes from the pressurized area of the high pressure outlet side of the positive displacement rotary pump, for example through tiny clearances and through the bearings of the axles of the wheels, and drain that fluid to the external of the housing of the pump, a so-called external case drain. The present inventor has realized that the drain can be utilized to prevent air locks of the pump. The drain can be used as a return channel to guide escaping lubricant back to the lubricant reservoir, and together with the lubricant, the smaller or larger air bubbles of the lubricant will escape as well. By providing the case drain flow path connecting the case drain port of the pump and the lubricant reservoir, from which the rotary pump draws lubricant, with a pressure relief valve being configured to open and allow fluid to flow towards the lubricant reservoir upon a predefined minimum fluid pressure being exceeded by fluid in the external case drain flow path, it is achieved that lubricant and air from the case drain port is only allowed back to the lubricant reservoir in small amounts at a time, thus splitting larger air bubbles into smaller air bubbles in lubricant of the lubricant reservoir. Hereby, the risk of larger air bubbles building up in the lubricant reservoir by being recirculated through the positive displacement rotary pump is eliminated since the feeding of larger air bubbles into the rotary pump from the lubricant reservoir is reduced, hereby reducing the risk of air lock of the rotary pump, which occurs when a sufficient number of air bubbles merges and fill a substantial part of the pressure area at the high pressure outlet side where the wheels merges.

[0010] Hence, the present disclosure in general relates to a hydraulic pump having an external drain channel with a pressure relief valve provided to control flow of fluid out of the case drain port and back into the lubricant reservoir. The positive displacement rotary pump is typically a gear pump, such as an external gear pump.

[0011] Thus, the present disclosure relates in a first aspect to a hydraulic pump for pumping fluid from a lubricant reservoir, the hydraulic pump comprising a positive displacement rotary pump having a housing, a low pressure inlet for connection to the lubricant reservoir and a high pressure outlet, a case drain port arranged to drain leakage from a high pressure side of the positive displacement rotary pump through the housing to an external side of the housing, an external case drain flow path connecting the case drain port and the lubricant reservoir, and a pressure relief valve located in the external case drain flow path, the pressure relief valve being configured to open and allow fluid to flow towards the lubricant reservoir upon a predefined minimum fluid pressure being exceeded by fluid in the external case drain flow path.

[0012] The pressure relief valve may in one embodiment be a one-way valve, such as a check valve. In general, the pressure relief valve is designed to open when the predefined minimum fluid pressure is exceeded and to close again when the fluid pressure is below the predefined minimum fluid pressure. In a specific embodiment, the pressure relief valve closes when the fluid pressure is below a closing fluid pressure, which is lower than the predefined minimum fluid pressure so that the pressure relief valve displays a certain hysteresis. With hysteresis of the pressure relief valve, the closing fluid pressure may e.g. be 0.5 bar or less lower than the predefined minimum fluid pressure, such as 0.2 bar or less lower.

[0013] The predefined minimum fluid pressure may in one embodiment be determined by the cracking pressure of the pressure relief valve. The cracking pressure is also known as the opening pressure and is the minimum pressure difference over the pressure relief valve that is required to open the valve sufficiently to allow for a detectable flow through the valve. Thus, in one embodiment, the pressure relief valve is controlled by the fluid pressure immediate upstream of the pressure control valve. In alternative embodiments, the pressure relief valve is controlled from the fluid pressure elsewhere in the external case drain flow path between the case drain port and the pressure relief valve.

[0014] In a particularly preferred embodiment, the hydraulic pump comprises an air buffer tank arranged in the external case drain flow path between the case drain port and the pressure relief valve. In case the hydraulic pump is equipped with a buffer tank, the predefined minimum fluid pressure may in one embodiment be measured in the air buffer tank and the opening of the pressure relief valve may be controlled by that measured pressure. The air buffer tank can be used as a temporary storage tank for returning lubricant and air bubbles, and the pressure relief valve can then be configured such that pressure is built up in the air buffer tank such that fluid is only allowed to flow from the air buffer tank towards the second end upon a predefined minimum pressure in the air buffer tank. The external case drain flow path and the air buffer tank constitute preferably a closed pipelined system with the lubricant reservoir constituting the only outlet from the closed pipeline system.

[0015] The external case drain flow path and / or the buffer flow path may in particular be formed by pipe(s) and / or hose(s).

[0016] Likewise, the external case drain flow path is preferably rigid, such as formed in a metallic material.

[0017] The predefined minimum pressure is preferably at least 2 bar, such as at least 3 bar, preferably at least 4 bars, more preferably at least 5 bars, most preferably at least 5.5 bar.

[0018] The predefined minimum pressure is preferably less than 10 bar, such as less than 8 bar, preferably less than 7 bars, more preferably less than 6.5 bars, most preferably between 5 and 7 bar, such as around 6 bar.

[0019] The air buffer tank has preferably a volume of at least 1 mL, such as at least 2 mL, more preferably at least 5 mL, most preferably at least 10 mL.

[0020] The air buffer tank has preferably a volume of less than 200 mL, such as less than 100 mL, more preferably less than 50 mL, most preferably between 2 mL and 100 mL.

[0021] The positive displacement rotary pump is in a preferred embodiment a gear pump, such as an external gear pump.

[0022] The hydraulic pump may comprise at least one electrical motor configured to drive the positive displacement rotary pump and a power supply and / or a controller for controlling the electrical motor so as to control the fluid flow through the rotary pump.

[0023] The hydraulic pump is advantageously configured as a portable system.

[0024] The present disclosure relates in a second aspect to a grease pump system for pumping lubricant grease, the system comprising one or more hydraulic pumps as disclosed herein, wherein at least one lubricant reservoir may comprises a lubricant grease. The grease pump system may for example be intended for filling lubrication systems of wind turbine generators or other heavy machinery, for example within the mining industry or harbour industry. The grease pump system may comprise at least one lubricant reservoir for containing a viscous fluid, such as lubricant grease. The viscous fluid, such as lubricant grease, may form part of the grease pump system.

[0025] The grease pump system may comprise at least one motor configured to drive the positive displacement rotary pump, as well as a power supply and / or a controller and / or a flow transmitter for controlling the amount of fluid through the rotary pump. The power supply may supply 12 V, 24 V or 48 V.

[0026] The presently disclosed grease pump system may be configured as a portable system. E.g. the elements of the grease pump system can be arranged in a portable box, possibly even comprising a handle for carrying the portable box. During operation, for example when the grease pump system is to be used to pump viscous fluid from a container to a lubrication system, the box is opened, a lubricant reservoir for viscous fluid, for example lubricant grease, is fluidly connected and fastened to the inlet flow path of the positive displacement rotary pump, and lubricant grease can then be pumped into the lubricating system by activating the motor.

[0027] According to a third aspect of the present disclosure, it relates to the user of the grease pump system disclosed herein for filling lubrication systems of wind turbine generators.

[0028] In a fourth aspect, the present disclosure relates to a method for reducing the risk of air locks of a hydraulic pump when supplying lubricant grease from a lubricant reservoir, the method comprising the steps of providing the grease pump system disclosed herein, operating the hydraulic pump to supply lubricant grease from the lubricant reservoir, guiding lubricant grease and air bubbles escaping through clearances in the positive displacement rotary pump via the case drain port and the external case drain flow path to the pressure relief valve, and releasing lubricant grease and air bubbles by means of opening the pressure relief valve when the fluid pressure upstream of the pressure relief valve reaches the predefined minimum pressure, thereby reducing the risk of air locks of the hydraulic pump. In case the external case drain flow path of the grease pump system comprises an air buffer tank as disclosed herein, the method comprises the steps of guiding lubricant grease and air bubbles escaping through clearances in the positive displacement rotary pump to the air buffer tank via the external case drain flow path thereby increasing the pressure in the air buffer tank, and releasing lubricant grease and air bubbles from the air buffer tank and back to the lubricant reservoir by means of the pressure relief valve when the pressure in the air buffer tank reaches the predefined minimum pressure, thereby reducing the risk of air locks of the hydraulic pump.

[0029] Hence, the present disclosure in general relates to a hydraulic pump having an external drain channel with an air buffer tank and a pressure control valve provided to control flow of fluid out of the air buffer tank. The positive displacement rotary pump is typically a gear pump, such as an external gear pump.

[0030] Brief description of the drawings

[0031] The present disclosure will in the following be described in greater detail with reference to the drawings. The drawings are exemplary and are intended to illustrate some of the features of the present method and system and are not to be construed as limiting to the present disclosure.

[0032] Fig. 1 illustrates a schematic diagram of the presently disclosed approach, Figs. 2A-2B illustrates an example of an external gear pump with external case drain port, and

[0033] Fig. 3 shows an example of a check valve.

[0034] Detailed description of an embodiment

[0035] An embodiment of the present disclosure is provided with reference to the drawings. Fig. 1 illustrates a schematic diagram of an embodiment of the presently disclosed hydraulic pump wherein the arrows illustrate the flow of lubricant though the system. The hydraulic pump comprises a positive displacement rotary pump 1 with an external case drain port 6. The flow of lubricant goes from lubricant reservoir 3 to the inlet 4 of the pump 1 via an inlet flow path 14 and further on to the outlet 5 of the pump and into an outlet flow path 15. Operation of the rotary pump 1 will suck lubricant from the reservoir 3 to the inlet 4 on the low-pressure side of the pump 1 and deliver the lubricant through the outlet 5 on the high-pressure side of the pump 1 . The lubricant reservoir 3 is not necessarily part of the presently disclosed hydraulic pump, because the lubricant reservoir 3 is normally only attached during operation of the pump.

[0036] A first part of the external case drain flow path 16 is connecting the external case drain port 6 of the pump 1 with an air buffer tank 2. The air buffer tank 2 collects air and lubricant that exits through the external case drain port 6.

[0037] A second part of the external case drain flow part 17, i.e. a buffer flow path 17 connects the air buffer tank 2 and the lubricant reservoir 3, but a pressure relief valve in the form of a one-way check valve 7 is provided in the buffer flow path 17. During operation of the pump 1 air and lubricant exiting from the drain 6 will slowly enter the air buffer tank 2. The check valve 7 ensures that only when the pressure in the air buffer tank 2 reaches the cracking pressure of the check valve 7, the external case drain flow path 16, 17 is opened for the content in the air buffer tank 2 to return to the lubricant reservoir 3. The cracking pressure of the check valve 7 is typically selected to be between 4 and 10 bar, such that the pressure in the air buffer tank 2 and in the first part of the external case drain flow path 16 is much lower that the pressure inside the rotary pump 1.

[0038] The check valve 7 with the cracking pressure ensures that the return of the drained air and lubricant grease to the lubricant reservoir 3 is provided in controlled manner, because only small bursts of lubricant grease and air will pass the check valve 7 in each opening of the valve 7, thus ensuring that larger bubbles of air will be divided into smaller bubbles of air.

[0039] In the presently disclosed approach the air buffer tank 2 functions as an "air-trap" in that the drained air and lubricant grease cannot return to the lubricant reservoir 3 until it has built up a sufficiently high pressure in the air buffer tank 2 to escape through the check valve 7. The underlying principle is that air is compressed under pressure. When there is high enough air pressure in the air buffer tank 2 (governed by the check valve), the valve will start to "crack" at the predefined cracking pressure. In practice, this means that the check valve 7 opens very little at a time, only in small bursts. This has the consequence that not all the air and lubricant grease in the air buffer tank 2 will be released back to the lubricant reservoir 3 at once, but in very small portions. I.e. returns in the form of larger air bubbles are avoided, and this will drastically reduce or eliminate the occurrence of air locks in the presently disclosed hydraulic pump.

[0040] Figs. 2 shows an example of an external gear pump 1 with external drain 6. Fig. 2A shows a cut-through side view of the pump 1 with the inlet 4 and the outlet 5 and the external drain 6. The external drain 6 is also illustrated in the end view in fig. 2B.

[0041] Fig. 3 shows a cut-through illustration of an example of a pressure relief valve 7 being a check valve 7 in the form of a screw-in, direct acting, ball type in-line check valve.

[0042] The check valve 7 comprises an inlet 12 and an outlet 9 to be inserted in the buffer flow path 17. The check valve 7 functions by means of a ball 10 and a spring 11 with a cartridge having a fully guided check, which is spring-biased, closed until sufficient pressure is applied at inlet 12 to open to outlet 9. The flow is blocked in the opposite direction, i.e. from outlet 9 to inlet 12.

[0043] The flow paths 14, 16 and 17 preferably form a closed pipelined system constituted of a non-flexible material such as metal, e.g. steel or aluminium.

[0044] List of reference numerals

[0045] 1 Positive displacement rotary pump

[0046] 2 Buffer tank

[0047] 3 Lubricant reservoir

[0048] 4 Inlet of rotary pump

[0049] 5 Outlet of rotary pump

[0050] 6 External case drain port

[0051] 7 Pressure relief valve

[0052] 8 Housing of positive displacement rotary pump

[0053] 9 Outlet of pressure relief valve

[0054] 10 Ball

[0055] 11 Spring

[0056] 12 Inlet of pressure relief valve

[0057] 14 Inlet flow path of rotary pump

[0058] 15 Outlet flow path of rotary pump

[0059] 16 First part of external case drain flow path

[0060] 17 Second part of external case drain flow path

Claims

Claims1 . A hydraulic pump for pumping fluid from a lubricant reservoir (3), the hydraulic pump comprising- a positive displacement rotary pump (1 ) having a housing (8), a low pressure inlet (4) for connection to the lubricant reservoir (3) and a high pressure outlet (5),- a case drain port (6) arranged to drain leakage from a high pressure side of the positive displacement rotary pump (1 ) through the housing (8) to an external side of the housing,- an external case drain flow path (16, 17) connecting the case drain port (6) and the lubricant reservoir (3), and- a pressure relief valve (7) located in the external case drain flow path (16, 17) , the pressure relief valve (7) being configured to open and allow fluid to flow towards the lubricant reservoir (3) upon a predefined minimum fluid pressure being exceeded by fluid in the external case drain flow path (16).

2. The hydraulic pump according to claim 1 , wherein the predefined minimum fluid pressure is determined by a cracking pressure of the pressure relief valve (7).

3. The hydraulic pump according to claim 1 or 2, comprising an air buffer tank (2) arranged in the external case drain flow path (16) between the case drain port (6) and the pressure relief valve (7).

4. The hydraulic pump according to claim 3, wherein the external case drain flow path (16, 17) and the air buffer tank (2) constitute a closed pipelined system with the lubricant reservoir (3) constituting the only outlet from the closed pipeline system.

5. The hydraulic pump according to any of the preceding claims, wherein the predefined minimum pressure is at least 2 bar, or at least 3 bar, preferably at least 4 bars, more preferably at least 5 bars, most preferably at least 5.5 bar.

6. The hydraulic pump according to any of the preceding claims, wherein the predefined minimum pressure is less than 10 bar, or less than 8 bar, preferably less than 7 bars, more preferably less than 6.5 bars, most preferably between 5and 7 bar, such as around 6 bar.

7. The hydraulic pump according to any of claims 3 to 6, wherein the air buffer tank (2) has a volume of at least 1 mL, preferably at least 2 mL, more preferably at least 5 mL, most preferably at least 10 mL.

8. The hydraulic pump according to any of claims 3 to 7, wherein the air buffer tank (2) has a volume of less than 200 mL, preferably less than 100 mL, more preferably less than 50 mL, most preferably between 2 mL and 100 mL.

9. The hydraulic pump according to any of the preceding claims, wherein the positive displacement rotary pump (1 ) is a gear pump, such as an external gear pump.

10. The hydraulic pump according to any of the preceding claims, comprising at least one electrical motor configured to drive the positive displacement rotary pump (1 ) and a power supply and / or a controller for controlling the electrical motor so as to control the fluid flow through the positive displacement rotary pump (1 ).11 . The hydraulic pump according to any of the preceding claims configured as a portable system.

12. A grease pump system for pumping lubricant grease, the system comprising the hydraulic pump according to any of the preceding claims, wherein the at least one lubricant reservoir (3) comprises a lubricant grease.

13. Use of the grease pump system according to claim 12, for filling lubrication systems of wind turbine generators.

14. A method for reducing the risk of air locks of a hydraulic pump when supplying lubricant grease from a lubricant reservoir (3), the method comprising the steps of- providing the grease pump system according to claim 12,- operating the hydraulic pump to supply lubricant grease from the lubricant reservoir (3),- guiding lubricant grease and air bubbles escaping through clearances in the positive displacement rotary pump (1 ) via the case drain port (6) and the external case drain flow path (16, 17) to the pressure relief valve (7), and- releasing lubricant grease and air bubbles by means of opening the pressure relief valve (7) when the fluid pressure upstream of the pressure relief valve (7) reaches the predefined minimum pressure, thereby reducing the risk of air locks of the hydraulic pump.

15. The method of claim 14, wherein the external case drain flow path (16, 17) comprises an air buffer tank (2) in accordance with claim 3, and wherein the method comprises the steps of- guiding lubricant grease and air bubbles escaping through clearances in the positive displacement rotary pump (1 ) to the air buffer tank (2) via the external case drain flow path (16) thereby increasing the pressure in the air buffer tank (2), and- releasing lubricant grease and air bubbles from the air buffer tank (2) and back to the lubricant reservoir (3) by means of the pressure relief valve (7) when the pressure in the air buffer tank (2) reaches the predefined minimum pressure, thereby reducing the risk of air locks of the hydraulic pump.

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