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EP-4735768-A1 - HYDRAULIC PUMP FOR PUMPING VISCOUS FLUID FROM A LUBRICANT RESERVOIR

EP4735768A1EP 4735768 A1EP4735768 A1EP 4735768A1EP-4735768-A1

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).

Inventors

  • LISBY, Thomas Hesselbjerg

Assignees

  • Hove A/S

Dates

Publication Date
20260506
Application Date
20240624

Claims (15)

  1. 1 . 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. 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. 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. 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. 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. 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 5 and 7 bar, such as around 6 bar.
  7. 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. 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. 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. 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. 11 . The hydraulic pump according to any of the preceding claims configured as a portable system.
  12. 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. 13. Use of the grease pump system according to claim 12, for filling lubrication systems of wind turbine generators.
  14. 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. 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.

Description

Hydraulic pump for pumping viscous fluid from a lubricant reservoir 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. Background 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. 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. 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. Summary 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. 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 cle