Balanced pressure seal for high pressure pump

Abstract

A pump includes a cylindrical plunger chamber having an inwardly projecting radial seal. The plunger moves in a reciprocating stroke within the cylindrical plunger chamber, the plunger having a first diameter and a second diameter less than the first diameter, and the radial seal engaging the plunger at the second diameter over the entire length of the stroke of the plunger. A pressure balance valve is in fluid communication with the pumping chamber and the hydraulic oil chamber. A fluid passage is connected to the plunger chamber at a location between the radial seal and the first diameter of the plunger and opens into the pressure balance valve. A radial clearance is between the cylinder and the second diameter, and a seal between the first portion and the cylinder having a smaller clearance than the radial clearance allows hydraulic fluid to leak through the seal during plunger stroke.

Description

Cross-reference to related applications

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 588,226, filed October 5, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to a sealing system for high-pressure pumps that balances pressure on the seal and prevents wear problems. Background Technology

[0003] Traditional positive displacement pumps used for pumping high-pressure liquids typically employ reciprocating plungers with packing to seal the pumped fluid. At high pressures (sometimes exceeding 10,000 psi), this packing is pressurized and pressed against the moving plunger with extremely high forces. This force generates high friction, leading to heat generation and rapid wear, which can cause failure. This situation is exacerbated when the fluid contains abrasive solid particles. In these high-pressure, abrasive fluid applications, the plunger, packing, and stuffing box experience wear and may even blister, resulting in costly and frequent maintenance. To minimize this problem, pressurized lubricant is supplied to the stuffing box to cool and lubricate the packing. While lubrication helps, it alone cannot eliminate the aforementioned problems.

[0004] One approach to trying to avoid this problem is to use a plunger pump, in which the plunger displaces only the oil, which in turn moves a diaphragm or piston, which in turn displaces the abrasive slurry. The plunger can be sealed against high pressure by a tight clearance with the cylinder, making the oil viscosity sufficient to maintain pressure even without seals. U.S. Patent 7,425,120 describes a pump in which a valve system holds the oil that displaces the diaphragm, resulting in only a small pressure differential across the diaphragm. However, this type of pump becomes less feasible for very high-pressure applications using large pumps due to the size of the diaphragm and the large chamber diameter that must accommodate the high pressure.

[0005] Because the pressure changes drastically between the pressure stroke and the intake, balancing the pressure on the seal is challenging for this arrangement. Furthermore, this sealing arrangement must prevent abrasive fluids from wearing down the seal.

[0006] Therefore, it should be understood that a new and improved sealing system is needed for high-pressure positive displacement pumps. This system should balance the pressure on the seals or packing in both the pressure and suction stroke, so that the seals are never pressurized and therefore never subjected to high forces on the plunger. Furthermore, the seals in this system should always have a low oil bias pressure to prevent abrasive fluids from wearing them. This invention solves these problems, as well as other problems associated with seals used in high-pressure pumps. Summary of the Invention

[0007] This invention relates to a positive displacement pump, such as a plunger pump. For multi-cylinder pumps, the pump is driven by a rotating crankshaft connected to a crankcase. The pump may include multiple plunger assemblies and associated components connected to the crankshaft. A manifold houses one or more check valves and inlet / outlet valves associated with each plunger assembly.

[0008] The plunger has a first portion having a first diameter (D1) that is formed to fit into the sleeve with a tight clearance (C). The clearance (C) is designed to be small enough that high-pressure oil can only pass through the clearance (C) very slowly. Typically, the clearance is measured radially and is approximately 0.001 inches. The plunger has a second portion having a second diameter (D2) that is slightly smaller than the first diameter. A low-pressure seal is positioned such that it contacts the second diameter (D2) throughout the plunger's stroke.

[0009] The fluid passage connects to the annular space (A) between the first diameter (D1) of the plunger and the seal. Due to the reciprocating motion of the plunger, the length of the annular space (A) changes during the stroke, resulting in a small discharge of oil from this space. The volume of discharge is defined by multiplying the area formed by the difference between diameters (D1) and (D2) by the plunger's stroke.

[0010] V=πL((Dl / 2) 2 -(D2 / 2) 2 )

[0011] Where: V is volume

[0012] D1 is the outer diameter.

[0013] D2 is the inner diameter.

[0014] L is the length of the plunger stroke.

[0015] The diameters (D1, D2) are configured such that the oil discharge is slightly greater than the maximum expected volume of oil that leaks through the gap (C) during the pump's pressure stroke.

[0016] In one embodiment, the plunger extends into the main pumping chamber. During the suction stroke, the plunger draws pumped fluid (such as water) into the chamber through an inlet check valve. During the pressure stroke, the plunger moves forward and removes fluid from the chamber through a discharge check valve. A pressure balancing valve is connected to the annular space (A) via a fluid passage. This valve is also connected to the pumping chamber via a passage.

[0017] In one embodiment, the pressure balancing valve includes a diaphragm connected to a valve spool. The valve spool slides in an orifice that connects to an oil chamber formed at least partially by the rear side of the diaphragm. The oil chamber is filled with oil and connected to both sides of the valve spool via passages within the valve spool. In another embodiment, the pressure balancing valve includes a piston assembly connected to a plunger. In yet another embodiment, the pressure balancing valve includes a plunger with complementary seals, instead of a diaphragm or piston.

[0018] The valve core is positioned to cover and expose both ports of the pressure balancing valve. The pressure balancing valve includes an outlet port connected to a pressure balancing outlet check valve, which allows oil to leave the oil chamber and flow into the oil reservoir. The pressure balancing valve also includes an inlet port connected to a pressure balancing inlet check valve, which allows oil to flow from the reservoir into the oil chamber.

[0019] A spring is positioned to apply a biasing force to the valve core, which in turn pulls the diaphragm. The front of the diaphragm faces the front chamber, which is connected to the pumping chamber via a channel. The pumping chamber, the front chamber, and the connecting channel are always filled with the pumped fluid, such as water.

[0020] According to one embodiment of the invention, a high-pressure sealing ring is used, which also provides a tight fit. High-pressure sealing rings may be necessary in larger high-pressure pumps where the amount of oil leaking through the tight fit of the plunger is too great. In such applications, metal piston rings can be used as sealing elements. Metal piston rings achieve a much longer lifespan than elastomeric seals while maintaining a lower leakage rate. Furthermore, since the high-pressure sealing ring seals only oil, it does not suffer the same wear as conventional packing. However, it should be understood that this type of seal may not be feasible for sealing pumped fluids (such as water) in conventional plunger pumps.

[0021] During operation, as the plunger reciprocates, the pumping chamber circulates between high pressure during the pressure stroke and low pressure during the suction stroke. Because the diaphragm is movable, the oil pressure within the chamber also circulates between suction and discharge pressures.

[0022] The function of a pressure balancing valve is to maintain a certain volume of oil behind the diaphragm, allowing the diaphragm to move freely and maintaining the oil pressure at the same level as the pumped fluid. The purpose of this invention is to maintain the oil pressure on the back of the seal, which is very close to the pressure in the pumping chamber. In this way, the seal is not pressurized and is not subjected to high frictional loads.

[0023] It is also beneficial to maintain an oil pressure slightly higher than the pumped fluid pressure. The benefit of a pressure differential of approximately 5 psi is that it always allows hydraulic oil, rather than the pumped fluid, to slip through the seals. In one example, during the suction stroke, the fluid pressure might be 10 psi as the plunger retracts, so the oil pressure would be 15 psi. On the pressure stroke, the fluid pressure might rise to 10,000 psi, so the oil pressure would be 10,005 psi. Therefore, as the plunger moves forward, this small pressure differential helps allow a very small amount of oil to leak through the valve, thus preventing the pumped fluid from passing through the seals. Similar benefits have been found in pressure differentials ranging from approximately 1 psi to 10 psi.

[0024] This small pressure differential is achieved by a force applied to the diaphragm by a spring. The spring is sized such that the force at the center position is equal to the force applied by the diaphragm, resulting in a 5 psi pressure differential across the diaphragm. During each pressure stroke, a small amount of oil leaks through the plunger clearance (C). Another advantage of this invention is that the valve can replenish the oil in the oil chamber as needed.

[0025] When the diaphragm is in the center position, the valve spool length allows it to cover both the pressure balance outlet port and the pressure balance inlet port. As oil drains from the oil chamber, the diaphragm moves backward, and the valve spool begins to expose the pressure balance inlet port. During the suction stroke, the pressure in the oil chamber drops, and oil is drawn in through the pressure balance inlet check valve. When the pump is pressure fed, the oil pressure may not drop sufficiently to draw in oil, so the diaphragm continues to move backward until it reaches the end of its stroke. At this point, a small displacement of space (A) will draw in oil, reducing the pressure as needed to draw it from the oil reservoir. If too much oil is drawn in, the diaphragm will move forward, closing the pressure balance inlet port and opening the pressure balance outlet port. During the next pressure stroke, oil will be discharged from the oil chamber via the pressure balance outlet check valve. When the pump is operating under steady-state conditions, the pressure balance valve will reach the equilibrium position, where the pressure balance inlet port is open just enough to add the required amount of oil to match the demand.

[0026] These novel features and various other advantages characterizing the invention are specifically pointed out in the appended claims, which form part of the invention. However, for a better understanding of the invention, its advantages, and the purposes achievable through its use, reference should be made to the accompanying drawings, which form another part of the invention, and the accompanying descriptive text, in which preferred embodiments of the invention are shown and described. Attached Figure Description

[0027] Referring now to the accompanying drawings, in several views the same reference letters and numbers indicate the corresponding structures:

[0028] Figure 1This is a perspective view of a first embodiment of a multi-cylinder plunger pump according to the principles of the present invention;

[0029] Figure 2 It is along Figure 1 A side sectional view of the axis of one of the cylinders of a multi-cylinder piston pump shown.

[0030] Figure 3 This is a cross-sectional view of an embodiment of a pump without high-pressure seals;

[0031] Figure 4 yes Figure 1 A cross-sectional view of the pressure balancing valve of the pump shown.

[0032] Figure 5 This is a cross-sectional view of an embodiment of a pump having a high-pressure seal that only contacts oil;

[0033] Figure 6 yes Figure 5 A side sectional view of the pump's plunger and seals shown;

[0034] Figure 7 yes Figure 6 Detailed side sectional view of the diameter steps of the seal and plunger shown;

[0035] Figure 8 yes Figure 2 A side sectional view of the pump's plunger and seals shown;

[0036] Figure 9 yes Figure 8 Detailed side sectional view of the diameter steps of the seal and plunger shown; and

[0037] Figure 10 This is a side sectional view of a plunger pump according to the principle of the present invention and having a pressure balancing valve, according to a second embodiment. Detailed Implementation

[0038] Now refer to the attached diagram, especially the reference... Figure 1 and Figure 2 A fluid pump (20) is shown. For a multi-cylinder pump, the pump (20) is driven by a rotating crankshaft (36) connected to a crankcase (22). The manifold 26 houses one or more check valves (54, 56). The pump (20) may include multiple pumping assemblies and associated components connected to the crankshaft (36).

[0039] Now for reference Figure 2A first embodiment of pump 20 includes a plunger assembly generally designated (30). The plunger assembly includes a plunger (42) that displaces the driven fluid. Hydraulic fluid (oil) is contained in a reservoir (28) and an oil reservoir (32). A sleeve (24) for the plunger (42) forms a cylindrical housing that partially defines the oil reservoir (32). Crankshaft (36) includes a connecting rod (38) attached to a slider (40) in crankcase (22). The slider (40) is connected to the plunger (42), which is actuated by crankshaft (36) and reciprocates to drive the hydraulic fluid. It will be understood that in some embodiments, crankshaft (36) may be attached to multiple different pumping assemblies (20) within the same pump and may include offset portions along the shaft such that the various pumping assemblies (20) pump synchronously at various stages of the pumping stroke. Figure 1 As shown, the pumped fluid is drawn into the manifold (26) through the manifold inlet channel (48), enters the pumping chamber (34), and is discharged by the plunger (42) through the manifold outlet channel (46).

[0040] like Figure 3 , Figure 8 and Figure 9 As shown, the plunger (42) has a first portion (42A) having a first diameter (D1) which is formed to fit tightly into the inner cylinder of the sleeve (24) with a very small clearance (C). The clearance (C) is designed to be small enough that the clearance allows high-pressure oil to pass through the clearance only very slowly. Typically, the clearance is measured radially and is approximately 0.001 inches. The plunger (42) has a second portion (42B) having a second diameter (D2) slightly smaller than the first diameter, with the clearance (C). A low-pressure seal (60) is positioned such that the low-pressure seal (60) contacts the second diameter (D2) throughout the entire stroke of the plunger (42).

[0041] The fluid passage (62) connects to the annular space (A) between the second diameter (D2) of the plunger and the seal (60), which extends radially outward from the second portion (42B) near the step up to the first portion (42A). Due to the reciprocating motion of the plunger (42), the length of the annular space (A) varies during the stroke, resulting in a small discharge of oil from this space. The volume of discharge is defined by multiplying the area formed by the difference between the diameters (D1) and (D2) by the plunger's stroke:

[0042] V=πL((Dl / 2) 2 -(D2 / 2) 2 )

[0043] Where: V is volume

[0044] D1 is the outer diameter.

[0045] D2 is the inner diameter.

[0046] L is the length of the plunger stroke.

[0047] The diameters (D1, D2) are configured such that the oil displacement is slightly larger than the maximum expected volume of oil leaking through the gap (C) during the pump's pressure stroke. It is understood that plungers and cylinders can also be implemented for... Figure 2 Piston pump (220).

[0048] The plunger (42) extends into the main pumping chamber (34). During the suction stroke, the plunger (42) draws pumped fluid (e.g., water) into the chamber (34) through the inlet check valve (54). During the pressure stroke, the plunger (42) moves forward and removes hydraulic fluid from the chamber (34) through the discharge check valve (56).

[0049] A pressure balancing valve (100) is connected to the annular space (A) via a fluid passage (62). The valve (100) is also connected to the pumping chamber (34) via a passage (112). Reference Figure 4 A first embodiment of the pressure balancing valve (100) includes a diaphragm (50) connected to a valve core (102). The valve core (102) slides in a bore (110) connected to an oil chamber (108) formed at least partially by the rear side of the diaphragm (50). The oil chamber (108) is filled with hydraulic fluid and is connected to both sides of the valve core (102) via a passage (106) within the valve core (102).

[0050] The valve core (102) is positioned to cover and expose both ports. The pressure balancing valve (100) includes an outlet port (120) connected to a pressure balancing outlet check valve (122), which allows hydraulic fluid to exit the oil chamber (108) and flow into the oil reservoir (32). The pressure balancing valve (100) also includes an inlet port (124) connected to a pressure balancing inlet check valve (126), which allows hydraulic fluid to flow from the reservoir (32) into the chamber (108).

[0051] A spring (104) is positioned to apply a biasing force to the valve core (102), which in turn pulls the diaphragm (50). The front of the diaphragm 50 faces the front chamber (130), which is connected to the pumping chamber (34) via a channel (112). The pumping chamber (34), the front chamber (130), and the connecting channel (112) are always filled with the pumped fluid, such as water.

[0052] In a second embodiment of the invention, the pressure balancing valve (200) includes a piston (250), which is drivably connected to the valve core (202) via a spring (104) between the valve core (202) and the piston (250). This embodiment of the pressure balancing valve (200) is similar to... Figure 2 The implementation method (100) is similar, but a piston (250) replaces the diaphragm (50) as the fluid displacement device. It is understood that other types of fluid displacement devices, such as plungers, can also be used.

[0053] refer to Figures 5 to 7 Another embodiment of the invention is shown, in which high-pressure sealing rings (44A, 44B, 44C) that also provide a tight fit are added. A configuration with a high-pressure sealing ring (44) may be necessary in larger high-pressure pumps where the amount of hydraulic fluid leaking through the tight fit of the plunger (42) is too large. In this case, metal piston rings are used as sealing elements (44A, 44B, 44C). Metal piston rings achieve a much longer lifespan than elastomeric seals while maintaining a small leakage rate. Furthermore, since the high-pressure sealing ring (44) seals only the hydraulic fluid, it does not suffer the same wear as conventional packing. However, it should be understood that this type of seal may not be feasible for sealing pumped fluids (such as water) in conventional plunger pumps.

[0054] operate

[0055] During operation, as the plunger (42) reciprocates, the pumping chamber (34) circulates between high pressure during the pressure stroke and low pressure during the suction stroke. Because the diaphragm (50) is movable, the pressure of the hydraulic fluid in the chamber (108) also circulates between suction pressure and discharge pressure.

[0056] A pressure balancing valve (100) maintains a certain volume of hydraulic fluid behind the diaphragm (50), allowing the diaphragm (50) to move freely and maintaining the hydraulic fluid pressure at the same level as the pumped fluid pressure. The purpose of this invention is to maintain a hydraulic fluid pressure on the back of the seal (60) that is very close to the pressure in the pumping chamber (34). In this way, the seal (60) is not pressurized and is not subjected to high frictional loads, thereby increasing the lifespan of the seal (60).

[0057] It has been found that maintaining a pressure slightly higher than the pumped fluid pressure is also beneficial. A pressure differential of approximately 5 psi provides the benefit of always allowing hydraulic fluid, rather than pumped fluid, to leak through the seal (60). In one example, during the suction stroke, as the plunger (42) retracts, the pumped fluid pressure might be 10 psi, so the hydraulic fluid pressure would be 15 psi. On the pressure stroke, the pumped fluid pressure might rise to 10,000 psi, so the hydraulic fluid pressure would be 10,005 psi. Thus, as the plunger (42) moves forward, this small pressure differential helps allow a very small amount of hydraulic fluid to leak through the valve, preventing pumped fluid from leaking through the seal (60). Furthermore, it has been found that pressure differentials ranging from approximately 1 psi to 10 psi can have similar benefits.

[0058] This small pressure differential is achieved by the force applied to the diaphragm by the spring (104). The spring (104) is sized such that the force at the center position is equal to the force applied by the diaphragm (50), which has a pressure differential of 5 psi across the diaphragm (50). During each pressure stroke, a small amount of oil leaks through the plunger clearance (C). Another advantage of the invention is that the valve (100) can replenish the hydraulic fluid in the oil chamber (108) as needed.

[0059] When the diaphragm (50) is in the centered position, the length of the valve core (102) allows the valve core to cover both the pressure balance outlet port (120) and the pressure balance inlet port (124). As hydraulic fluid flows out of the oil chamber (108), the diaphragm (50) moves backward (towards)... Figure 4 The diaphragm (50) moves to the left, and the valve core (102) will begin to expose the pressure balance inlet port (124). During the suction stroke, the pressure in the oil chamber 108 drops and hydraulic fluid is drawn in through the pressure balance inlet check valve (126). In applications where the pump is pressure-supplying, the pressure of the hydraulic fluid may not drop sufficiently to draw in oil, so the diaphragm (50) will continue to move backward until the diaphragm reaches the end of its stroke. At this point, a small displacement of the space (A) draws in hydraulic fluid, reducing the pressure as needed to draw it from the oil reservoir (32). If too much hydraulic fluid is drawn in, the diaphragm (50) will move forward, which will close the pressure balance inlet port (124) and open the pressure balance outlet port (120). During the next pressure stroke, hydraulic fluid will be discharged from the oil chamber (108) via the pressure balance outlet check valve (122). When the pump (20) is operating under steady-state conditions, the pressure balance valve (100) will reach the balance position, where the pressure balance inlet port (124) is open just enough to add the amount of hydraulic fluid required to match the demand.

[0060] However, it should be understood that although many features and advantages of the invention, as well as details of its structure and function, have been set forth in the foregoing description, this disclosure is merely illustrative and changes in detail may be made within the full scope indicated by the broad meaning of the terms in the appended claims, particularly changes in the shape, size, and arrangement of the components, within the principles of the invention.

Claims

1. A pump comprising: A cylindrical plunger chamber having an inwardly projecting radial seal; A plunger that moves reciprocally within a cylindrical plunger chamber, the plunger having a first diameter and a second diameter smaller than the first diameter, and a radial seal engaging the plunger at the second diameter over the entire length of the plunger's stroke; A pressure balancing valve, which is in fluid communication with the pumping chamber and the hydraulic oil chamber; A fluid passage provides fluid communication between the plunger chamber and the pressure balancing valve, the fluid passage being connected to the plunger chamber at a location between the radial seal and the first diameter of the plunger.

2. The pump according to claim 1, wherein the plunger comprises: A first portion having a first diameter and a second portion having a second diameter smaller than the first diameter, the second portion being closer to the free end of the plunger; A first radial seal engages the first portion of the plunger; A second radial seal engages with the second portion of the plunger; A radial volume defined between the plunger chamber and the second portion of the plunger diameter and between the second seal and the first portion of the plunger.

3. The pump of claim 1, wherein the radial seal comprises one or more metal piston rings.

4. The pump of claim 1, wherein the pressure balancing valve includes a valve core that slides in an orifice to cover and expose a hydraulic fluid inlet port and a hydraulic fluid outlet port.

5. The pump according to claim 4, wherein: Under the first operating condition, hydraulic fluid is drawn in through the gap space between a portion of the plunger and the cylindrical plunger chamber; Under the second operating condition, the inlet port of the pressure balancing valve is open; Under the third operating condition, the outlet port of the pressure balancing valve is open.

6. The pump according to claim 4, wherein: The pressure balancing valve includes a diaphragm having a pumping side and an oil side, the oil side having a hydraulic oil chamber partially formed by the oil side of the diaphragm.

7. The pump of claim 6, further comprising a spring located between the valve core and the diaphragm and applying a biasing force to the diaphragm.

8. The pump of claim 7, wherein the spring is configured to apply a force of about 5 psi when the diaphragm is in the centered position.

9. The pump according to claim 4, wherein: The pressure balancing valve includes a piston having a pumping side and an oil side, the oil side having a hydraulic oil chamber partially formed by the oil side of the piston.

10. A pressure balancing system for a pump having a hydraulic fluid reservoir, the pressure balancing system comprising: An orifice in fluid communication with the oil chamber; plunger; A plunger chamber having a seal between the plunger and the plunger chamber; A fluid passage from the plunger chamber to the orifice; A pressure balancing valve in fluid communication with the orifice, the valve comprising: An outlet port, wherein the outlet port includes an outlet check valve; Inlet port, the inlet port including an inlet check valve; A valve core that slides within the orifice to cover and expose the inlet port and the outlet port.

11. The pressure balancing system of claim 10, further comprising a fluid displacement device having a pump side and an oil side.

12. The pressure balancing system of claim 11, further comprising a spring located between the valve core and the fluid displacement device and applying a biasing force to the fluid displacement device.

13. The pressure balancing system of claim 12, wherein the spring is configured to apply a force of approximately 5 psi when the fluid displacement device is in the central position.

14. The pressure balancing system of claim 11, wherein the fluid displacement device comprises a diaphragm.

15. The pressure balancing system of claim 11, wherein the fluid displacement device comprises a piston.

16. A plunger pump comprising: A plunger having a hydraulic side and a pumping side; An oil chamber located on the hydraulic side of the plunger, the oil chamber containing hydraulic fluid; An orifice in fluid communication with the oil chamber; An outlet port, wherein the outlet port includes an outlet check valve; Inlet port, the inlet port including an inlet check valve; A valve core that slides within the orifice to cover and expose the inlet port and the outlet port; A plunger chamber having a seal between the plunger and the plunger chamber; A fluid passage from the plunger chamber to the orifice.

17. The plunger pump of claim 16, wherein the plunger comprises: A first portion having a first diameter and a second portion having a second diameter smaller than the first diameter, the second portion being closer to the free end of the plunger; A first seal engages with the first portion of the plunger; A second seal engages with the second portion of the plunger; Radial volume, the radial volume being defined between the plunger chamber and the second diameter.

18. The plunger pump according to claim 16, wherein: Under the first operating conditions, hydraulic fluid is drawn in through the radial volume; Under the second operating condition, the inlet port of the pressure balancing valve is open; Under the third operating condition, the outlet port of the pressure balancing valve is open.

19. The plunger pump of claim 16, wherein the plunger comprises a first portion having a first diameter and a second portion having a second diameter smaller than the first diameter, the second portion being closer to the free end of the plunger; A first seal engages with the first portion of the plunger; A second seal engages with the second portion of the plunger; A radial volume between the plunger chamber and the second portion of the plunger diameter and the second seal and the first portion of the plunger.

20. The plunger pump of claim 19, wherein the first seal comprises one or more metal piston rings.

21. A plunger pump, comprising: A plunger having a hydraulic side and a pumping side; An oil chamber located on the hydraulic side of the plunger, the oil chamber containing hydraulic fluid; The plunger includes a first portion having a first diameter and a second portion having a second diameter smaller than the first diameter, the second portion being closer to the free end of the plunger; The radial clearance located between the cylinder and the second diameter.

22. The plunger pump of claim 21, comprising: A seal located between the first portion and the cylinder, the seal having a gap smaller than the radial clearance, and configured to allow hydraulic fluid to leak through the seal during the stroke of the plunger.

23. The plunger pump of claim 22, wherein the first diameter and the second diameter are configured such that the hydraulic fluid displacement is slightly greater than the maximum expected volume of hydraulic fluid leaking through the gap during the pressure stroke of the pump.

24. The plunger pump of claim 23, wherein the volume of hydraulic fluid discharged during the stroke of the plunger is defined by multiplying the area formed by the difference between the first diameter (D1) and the second diameter (D2) by the stroke of the plunger: V=πL((Dl / 2) 2 -(D2 / 2) 2 ) in: V is the volume. D1 is the outer diameter. D2 is the inner diameter. L is the length of the plunger stroke.

25. The plunger pump of claim 21, comprising a second seal located between the second portion and the cylinder, wherein the second portion, the second seal, the cylinder, and the step extending up to the first portion form a chamber, the volume of which is at least as large as the volume of hydraulic fluid allowed to leak through the seal during the stroke of the plunger.

26. The plunger pump of claim 22, wherein the seal comprises one or more metal piston rings.

27. A method of operating a plunger pump, the plunger pump comprising a reciprocating plunger having a hydraulic side and a pumping side; An oil chamber located on the hydraulic side of the plunger, the oil chamber containing hydraulic fluid; A plunger located in a cylinder drives hydraulic fluid against the diaphragm. The plunger includes a first portion having a first diameter and a second portion having a second diameter smaller than the first diameter, the second portion being closer to the free end of the plunger. A radial clearance between the cylinder and the second diameter, and a seal located between the first portion and the cylinder, the seal having a clearance smaller than the radial clearance and configured to allow hydraulic fluid to leak through the seal during the stroke of the plunger; the method includes: Hydraulic fluid is allowed to leak through the seal; A certain amount of hydraulic fluid is supplied to replace the leaking hydraulic fluid with a volume equal to the interval formed by the second seal between the second portion and the cylinder, wherein the second portion, the second seal, the cylinder, and the step up to the first portion form a chamber, the volume of which is at least as large as the volume of hydraulic fluid allowed to leak through the seal during the stroke of the plunger.

28. The method of claim 27, wherein the pressure balancing valve comprises a hydraulic fluid inlet port and a hydraulic fluid outlet port, wherein: Under the first operating conditions, hydraulic fluid is drawn in through the radial volume; Under the second operating condition, the pressure balancing valve opens the hydraulic fluid inlet port; Under the third operating condition, the pressure balancing valve opens the hydraulic fluid outlet port.

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