Accurate differential hydraulic control system for pile hammer

Abstract

The application discloses a precise differential hydraulic control system for a pile hammer, wherein a hydraulic power oil source is communicated with a differential cartridge valve working cavity of a differential cartridge valve below a hydraulic cylinder lower cavity and a differential cartridge valve ring cavity of the differential cartridge valve and a return oil cartridge valve working cavity of a return oil cartridge valve are communicated with a hydraulic cylinder upper cavity of the hydraulic cylinder respectively, a return oil cartridge valve ring cavity of the return oil cartridge valve is communicated with a return oil tank, the hydraulic power oil source is communicated with the differential control valve and the differential cartridge valve after throttling, the differential control valve is communicated with the hydraulic cylinder upper cavity of the hydraulic cylinder, the hydraulic power oil source is communicated with a pressure oil port P of an electromagnetic control valve, a working oil port A of the electromagnetic control valve is communicated with a return oil cartridge valve control cavity of the return oil cartridge valve, a working oil port B of the electromagnetic control valve is communicated with a control oil port K of the differential control valve, and a return oil port T of the electromagnetic control valve is communicated with the return oil tank. The precise differential hydraulic control system has the advantages of fast response speed, high striking frequency, small pressure and flow loss of hydraulic oil and large striking energy.

Description

Technical Field

[0001] This invention relates to a hydraulic piling machine, and more particularly to a hydraulic control system for a hydraulic piling hammer having a hydraulic cartridge valve and a differential hydraulic cylinder. Background Technology

[0002] A hydraulic pile driver is a type of pile driving machinery powered by hydraulic oil pressure. Hydraulic pile drivers are characterized by high energy efficiency, strong controllability, and excellent environmental performance. Their energy transmission efficiency is significantly higher than that of diesel pile drivers, greatly reducing energy waste. Furthermore, hydraulic pile drivers can control their striking energy, frequency, and stroke through an electronic control system, achieving "heavy hammer, light hammer" or "light hammer, heavy hammer" operation, adapting to different soil layers and pile types, and effectively avoiding pile damage. They are widely used in pile foundation construction in fields such as building construction, bridges, ports, and marine engineering.

[0003] The hydraulic pile hammer uses a differentially connected hydraulic cylinder, which can achieve a higher movement speed under low flow conditions. In addition to gravity, the hammer core is also subjected to a downward hydraulic thrust from the piston when the hammer falls, making the pile hammer strike greater. Therefore, the differential hydraulic pile hammer has a higher striking frequency and striking energy.

[0004] The striking performance and efficiency of a hydraulic pile hammer are directly related to the design of its hydraulic control system. Currently, most hydraulic pile hammers use cartridge valves and solenoid valves to form the hydraulic control circuit. However, in actual use, the hydraulic control system still has some defects and shortcomings: First, parallel interconnected control valves are prone to interference and "route grabbing" phenomena. When the pressure and flow rate in the two control valve pipelines are different, the pipeline with higher flow rate and pressure will force the cartridge control valve connected to the pipeline with lower flow rate and pressure to fail to release pressure in time. This results in the hydraulic cylinder moving weakly, slowly, or even not moving at all, leading to unstable movement, creeping, or "response delay" of the hydraulic cylinder and hammer core. The lag in the response of the control valve will greatly affect the striking frequency and efficiency of the hydraulic hammer. Secondly, the high-pressure oil used to drive the control valves in the control system flows directly back to the return oil tank, increasing the flow load of the hydraulic power source. While a portion of the high-pressure oil from the hydraulic power source enters the hydraulic cylinder to drive it, another portion flows back to the control pipeline. This backflow and diversion of high-pressure oil causes fluctuations and drops in pressure in the main oil circuit leading to the hydraulic cylinder, resulting in pressure and flow losses in the hydraulic oil. This weakens the hammer's impact and reduces its striking force. Thirdly, the control oil circuits of multiple control valves are connected in parallel to the same working port of the solenoid control valve. While this may make the structure more compact, the different loads on each control valve lead to uneven flow distribution, causing interference and affecting their synchronization. Furthermore, flow competition between two control valves causes asynchronous pressure drops, resulting in response lag and poor dynamic response of the control loop, which in turn affects the striking frequency of the pile hammer. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a precision differential hydraulic control system for pile driving hammers, which not only has a fast response speed and high striking frequency, but also has low pressure and flow loss of hydraulic oil and large striking energy.

[0006] To solve the above-mentioned technical problems, the present invention provides a precision differential hydraulic control system for pile driving hammers, comprising a hydraulic cylinder and a hydraulic power source, wherein the hydraulic cylinder is divided into a lower hydraulic cylinder chamber and an upper hydraulic cylinder chamber by a piston.

[0007] The hydraulic power source is connected to the lower chamber of the hydraulic cylinder and the working chamber of the differential cartridge valve:

[0008] The upper chamber of the hydraulic cylinder is connected to the differential cartridge valve annular chamber of the differential cartridge valve and the return oil cartridge valve working chamber of the return oil cartridge valve, respectively. The return oil cartridge valve annular chamber of the return oil cartridge valve leads to the return oil tank.

[0009] The hydraulic power source is connected to the pressure port P of the differential control valve and the differential cartridge valve control chamber of the differential cartridge valve after passing through the throttle valve. The working port A of the differential control valve is connected to the upper chamber of the hydraulic cylinder.

[0010] The hydraulic power source is also connected to the pressure port P of the solenoid control valve. The working port A of the solenoid control valve is connected to the control chamber of the return cartridge valve. The working port B of the solenoid control valve is connected to the control port K of the differential control valve. The return port T of the solenoid control valve is connected to the return tank.

[0011] Preferably, the control system includes at least two differential cartridge valves.

[0012] Furthermore, the differential cartridge valve working chambers of each differential cartridge valve are connected in parallel to the lower chamber of the hydraulic cylinder, the annular chambers of each differential cartridge valve are connected in series to the upper chamber of the hydraulic cylinder and the working chamber of the return oil cartridge valve, and the control chambers of each differential cartridge valve are connected to the pressure port P of the differential control valve.

[0013] Furthermore, the upper chamber of the hydraulic cylinder is connected to the working chamber of the return oil cartridge valve via the annular chamber of the differential cartridge valve.

[0014] Preferably, the lower chamber of the hydraulic cylinder is connected to the annular chamber of the safety cartridge valve and the control chamber of the safety cartridge valve, respectively, and the working chamber of the safety cartridge valve is connected to the upper chamber of the hydraulic cylinder and the annular chamber of the differential cartridge valve.

[0015] Preferably, the throttle valve is an adjustable throttle valve or a fixed throttle valve.

[0016] Preferably, the differential control valve is a normally closed or normally open two-position two-way hydraulic control valve.

[0017] Preferably, the electromagnetic control valve is a two-position four-way electromagnetic valve.

[0018] Preferably, the electromagnetic control valve is a two-position four-way dual-electro-controlled electromagnetic valve.

[0019] Furthermore, the return port T of the electromagnetic control valve is connected to the return oil tank via a return oil check valve, the lower chamber of the hydraulic cylinder is also connected to the inlet bypass accumulator, and the annular chamber of the return oil cartridge valve is connected to the return oil bypass accumulator.

[0020] After adopting the above technical solution, the control system of the present invention uses an electromagnetic control valve and a hydraulically controlled differential control valve. The electromagnetic control valve, as the main valve, can independently control two types of sub-valves: the differential control valve and the return oil cartridge valve. The differential control valve and the return oil cartridge valve are controlled by different control ports of the electromagnetic control valve. This changes the shortcomings of traditional control systems, such as the difficulty in achieving precise position and speed synchronization when multiple sub-valves are controlled by the same control port. It not only overcomes the uneven distribution of oil supply flow caused by different parameters such as pressure, flow rate and load of different sub-valves, which affects the synchronization and coordination of actions, but also overcomes the response lag caused by flow competition among multiple sub-valves. It effectively improves control accuracy, ensures dynamic response, and is conducive to realizing high-frequency hammering of the pile driver.

[0021] Furthermore, due to the addition of a throttle valve in the control circuit, the high-pressure oil from the pressure oil source flows back to the differential control valve after being throttled by the throttle valve. This throttling effect ensures that the high-pressure oil in the control chamber of the differential cartridge valve flows back and depressurizes first, allowing the differential cartridge valve to open quickly. After the hammer core of the pile driver is raised to its highest point, it needs to be dropped quickly downwards immediately to obtain higher striking energy. The differential cartridge valve needs to respond quickly and conduct at this reversal moment to form a differential circuit. However, since the high-pressure oil from the hydraulic power source is simultaneously delivered to the working chamber and control chamber of the differential cartridge valve through the main oil pipe and control oil pipe respectively, the pressure on both ends of the differential cartridge valve core is equal or similar. The sliding thrust acting on the differential cartridge valve core is very small, and the valve core is prone to "creeping" and slow response. This seriously affects the response speed of the differential cartridge valve, resulting in response delay and sluggish reaction, which severely affects the increase of the pile driver's striking frequency. By using a throttle valve, its throttling effect can be utilized. At the moment of hammer core reversal, the oil pressure in the working chamber of the differential cartridge valve is briefly higher than the oil pressure in the control chamber of the differential cartridge valve. Driven by this pressure difference, the valve core of the differential cartridge valve responds quickly and opens to form a differential circuit, thereby accelerating the rapid downward fall of the pile hammer core and increasing the striking frequency and striking force of the pile hammer.

[0022] Furthermore, because the working port of the differential control valve is connected to the upper chamber of the hydraulic cylinder, the high-pressure control oil from the hydraulic power source does not flow back to the oil tank, causing pressure loss, but instead flows to the upper chamber of the hydraulic cylinder. When the pile hammer falls, the control oil circuit enters a differential state. Since the effective area of ​​the upper chamber of the hydraulic cylinder is larger than that of the lower chamber, the high-pressure oil from the hydraulic power source simultaneously enters both the lower and upper chambers of the hydraulic cylinder. The oil supplied by the hydraulic power source, the oil in the lower chamber of the hydraulic cylinder, and the return oil from the differential control valve converge and flow to the upper chamber of the hydraulic cylinder, increasing the flow rate. This not only accelerates the rapid downward movement of the piston and the hammer's fall but also increases the downward hydraulic impact of the piston, which is beneficial for increasing the striking frequency and striking energy. The return of the high-pressure control oil to the upper chamber of the hydraulic cylinder reduces the flow and pressure losses in the high-pressure oil circuit, allowing the high-pressure control oil to also convert into striking energy, reducing the load on the high-pressure oil source and the power consumption of the pile hammer, and improving energy conversion efficiency.

[0023] The control system of this invention can achieve precise control of the pile driving hammer. It can not only accurately control the lifting height of the hammer core and the frequency of the hammer core's reciprocating motion, but also has a large flow capacity, low energy loss, and can accurately regulate the required striking energy and the repeatability of the strike. Attached Figure Description

[0024] The precise differential hydraulic control system for pile driving hammers of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 This is a control principle diagram of the precision differential hydraulic control system for pile driving hammers of the present invention;

[0026] Figure 2 This is a schematic diagram illustrating the working principle of the hammer lifting state according to a specific embodiment of the present invention;

[0027] Figure 3 yes Figure 2 The diagram illustrates the working principle of the falling hammer in the embodiment shown.

[0028] In the diagram, 1—hydraulic power source, 2—inlet check valve, 3—inlet bypass accumulator, 4—hydraulic cylinder, 5—lower chamber of hydraulic cylinder, 6—upper chamber of hydraulic cylinder, 7—safety cartridge valve, 8—safety cartridge valve control chamber, 9—safety cartridge valve annular chamber, 10—safety cartridge valve working chamber, 11—differential cartridge valve, 12—differential cartridge valve control chamber, 13—differential cartridge valve annular chamber, 14—differential cartridge valve working chamber, 15—throttle valve, 16—differential control valve, 17—return cartridge valve, 18—return cartridge valve control chamber, 19—return cartridge valve annular chamber, 20—return cartridge valve working chamber, 21—solenoid control valve, 22—return check valve, 23—return bypass accumulator, 24—return tank. Detailed Implementation

[0029] Figure 1 The illustrated precision differential hydraulic control system for a pile driver includes a hydraulic cylinder 4 and a hydraulic power source 1. The hydraulic cylinder 4 employs a double-rod piston structure, with a piston slidably supported within the cylinder chamber of the hydraulic cylinder 1, dividing the chamber into an upper chamber 6 and a lower chamber 5. The piston rod diameter on the upper side of the piston is smaller than that on the lower side of the piston to form a differential hydraulic connection circuit. The extended end of the piston rod on the lower side of the piston is connected to the hammer core of the pile driver. The hydraulic power source 1 includes a hydraulic pump supplying pressurized oil, a drive motor, an oil tank, an overflow valve, and a cooling system, etc. The hydraulic power source 1 of this invention represents a commonly used structure in hydraulic control systems for hydraulic pile drivers.

[0030] The precision control system of the present invention also includes an electromagnetic control valve 21, a differential control valve 16, a return oil cartridge valve 17, a differential cartridge valve 11, and a safety cartridge valve 7.

[0031] The solenoid control valve 21 is a two-position four-way dual-electro-controlled solenoid valve, which has higher control stability. The solenoid control valve 21 includes a pressure port P, a return port T, a working port A, and a working port B. In addition to the two-position four-way dual-electro-controlled solenoid valve, the solenoid control valve 21 can also be a two-position four-way solenoid valve with other structures.

[0032] The differential control valve 16 is a normally open two-position two-way hydraulic control valve. The differential control valve 16 includes a pressure oil port P, a working oil port A, and a control oil port K. The differential control valve 16 can also be a normally closed two-position two-way hydraulic control valve.

[0033] The return cartridge valve 17, differential cartridge valve 11, and safety cartridge valve 7 all adopt a cartridge structure, which not only has a simple valve core structure and strong versatility, but also has sensitive operation and good sealing performance. The return cartridge valve 17, differential cartridge valve 11, and safety cartridge valve 7 all include corresponding control chambers, annular chambers, and working chambers.

[0034] The control system also includes an inlet check valve 2, a return check valve 22, an inlet bypass accumulator 3, and a return bypass accumulator 23; the check valves and accumulators mentioned above are all of the type of hydraulic control components commonly used in hydraulic pile hammers.

[0035] The high-pressure port of the hydraulic power source 1 is connected to the lower chamber 5 of the hydraulic cylinder through a high-pressure oil pipe and an inlet check valve 2; and the high-pressure outlet of the hydraulic power source 1 is also connected to the differential cartridge valve working chamber 14 of the differential cartridge valve 11 through a high-pressure oil pipe.

[0036] The upper chamber 6 of hydraulic cylinder 4 is connected via a high-pressure oil pipe to the differential cartridge valve annular chamber 13 of differential cartridge valve 11 and the return cartridge valve working chamber 20 of return cartridge valve 17. Furthermore, the differential cartridge valve annular chamber 13 of differential cartridge valve 11 is connected to the return cartridge valve working chamber 20 of return cartridge valve 17. The return cartridge valve annular chamber 19 of return cartridge valve 17 is connected to the return oil tank 24.

[0037] The control system of this invention also includes a safety cartridge valve 7. The annular chamber 9 and control chamber 8 of the safety cartridge valve 7 are connected to the lower chamber 5 of the hydraulic cylinder. The working chamber 10 of the safety cartridge valve 7 is connected to the upper chamber 6 of the hydraulic cylinder and the annular chamber 13 of the differential cartridge valve 11. When the pile hammer is at its lowest position and the differential cartridge valve 11 and the return cartridge valve 17 are in the momentary closed state during reversal, if the pile being struck rebounds, the pressure in the upper chamber 6 of the differential hydraulic cylinder will be in a momentary pressure-stagnant state. At this time, the safety cartridge valve 7 will open, connecting the upper chamber and the lower chamber of the hydraulic cylinder. The inlet bypass accumulator 3 absorbs the vibration pulse, thus playing a damping role.

[0038] The hydraulic power source 1 is also connected to the pressure port P of the solenoid control valve 21 via a control oil pipe. The return port T of the solenoid control valve 21 is connected to the return oil tank 24 via the return check valve 22. The working port A of the solenoid control valve 21 is connected to the return oil cartridge valve control chamber 18 of the return oil cartridge valve 17. The working port B of the solenoid control valve 21 is connected to the control port K of the differential control valve 16.

[0039] The hydraulic power source 1, after passing through the throttle valve 15, flows to the differential cartridge valve control chamber 12 of the differential cartridge valve 11 and the pressure port P of the differential control valve 16; or, at the moment of reversal, the oil in the differential cartridge valve control chamber 12 of the differential cartridge valve 11 merges with the oil from the hydraulic power source 1 after passing through the throttle valve 15 and flows to the pressure port P of the differential control valve 16. The working port A of the differential control valve 16 is connected to the upper chamber 6 of the hydraulic cylinder 4. In the actual structure, the working port A of the differential control valve 16 is connected to the high-pressure oil pipe that connects the differential cartridge valve annular chamber 13 of the differential cartridge valve 11 and the return oil cartridge valve working chamber 20 of the return oil cartridge valve 17 via a control oil pipe, and this high-pressure oil pipe also leads to the upper chamber 6 of the hydraulic cylinder 4.

[0040] like Figure 2As shown, the precision control system in this embodiment includes two parallel differential cartridge valves 11. The differential cartridge valve control chambers 12 of these two differential cartridge valves 11 are connected in parallel to the pressure port P of the differential control valve 16, meaning both differential cartridge valve control chambers 12 are connected to the pressure port P of the differential control valve 16. The annular chambers 13 of the differential cartridge valves 11 are connected in series to the return cartridge valve working chamber 20 of the return cartridge valve 17. The differential cartridge valve working chambers 14 of the two differential cartridge valves 11 are connected in parallel to the lower chamber 5 of the hydraulic cylinder and the high-pressure port of the hydraulic power source 1.

[0041] When the solenoid control valve 21 is in the working position shown in the figure, the high-pressure oil from the hydraulic power source 1 flows sequentially through the pressure port P and the working port B of the solenoid control valve 21 to the control port K of the differential control valve 16, and the differential control valve 16 is in the closed state.

[0042] The return oil cartridge valve control chamber 18 of the return oil cartridge valve 17 is connected to the return oil tank 24 in sequence through the working oil port A of the solenoid control valve 21, the return oil port T, and the return oil check valve 22. The return oil cartridge valve 17 is in the open state.

[0043] The high-pressure oil from the hydraulic power source 1 also enters the differential cartridge valve control chamber 12 of the differential cartridge valve 11 through the control oil pipe and its throttle valve 15, so that both differential cartridge valves 11 are in the closed state.

[0044] At this time, the high-pressure oil from the hydraulic power source 1 flows to the lower chamber 5 of the hydraulic cylinder and pushes the piston of the hydraulic cylinder 24 upward; the oil in the upper chamber 6 of the hydraulic cylinder flows back to the return oil tank 24 through the return oil cartridge valve working chamber 20 and the return oil cartridge valve annular chamber 19 of the return oil cartridge valve 17. At this time, the pile hammer is in the hammer lifting working state.

[0045] like Figure 3 As shown, when the solenoid control valve 21 is in the illustrated working position, the differential control valve 16 is in the open state, and the return cartridge valve 17 is in the closed state. Due to the throttling effect of the throttle valve 15, the differential cartridge valve control chamber 12 of the differential cartridge valve 11 is depressurized instantaneously through the open differential control valve 16, causing both differential cartridge valves 11 to quickly enter the open state.

[0046] With the return cartridge valve 17 closed and the differential cartridge valve 11 open, the hydraulic cylinder 4 is in a differential operating state. High-pressure oil from the hydraulic power source 1 enters both the upper chamber 6 and the lower chamber 5 of the hydraulic cylinder simultaneously via the open differential cartridge valve 11. Since the effective area of ​​the upper chamber 6 is larger than that of the lower chamber 5, the high-pressure oil in the lower chamber 5 flows back to the upper chamber 6. Simultaneously, pressure oil from the hydraulic power source 1 also flows back to the upper chamber 6 via the control oil pipe through the pressure port P and working port A of the throttle valve 15 and the differential control valve 16, creating a flow superposition effect. This allows the hydraulic cylinder 4 to achieve a higher downward speed with a smaller input flow, thereby increasing the impact force energy. At this time, the pile hammer is in the falling hammer operating state.

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the preferred embodiments above, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention. For example, in addition to using a double-rod hydraulic cylinder, the hydraulic cylinder can also be a single-rod hydraulic cylinder or other types of hydraulic cylinders; in the hydraulic control system, one or two differential cartridge valves can be used, and multiple differential cartridge valves can be connected in parallel according to the design requirements of the flow rate; in addition to using a two-position two-way hydraulic control valve, the differential control valve can also be a sequence valve. These do not depart from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A precision differential hydraulic control system for a pile driver, comprising a hydraulic cylinder (4) and a hydraulic power source (1), wherein the hydraulic cylinder (4) is divided by a piston into a lower chamber (5) and an upper chamber (6), characterized in that: The hydraulic power source (1) is connected to the lower chamber (5) of the hydraulic cylinder and the differential cartridge valve working chamber (14) of the differential cartridge valve (11): The upper chamber (6) of the hydraulic cylinder is connected to the differential cartridge valve annular chamber (13) of the differential cartridge valve (11) and the return oil cartridge valve working chamber (20) of the return oil cartridge valve (17), respectively. The return oil cartridge valve annular chamber (19) of the return oil cartridge valve (17) leads to the return oil tank (24). The hydraulic power source (1) is connected to the pressure port P of the differential control valve (16) and the differential cartridge valve control chamber (12) of the differential cartridge valve (11) after passing through the throttle valve (15). The working port A of the differential control valve (16) is connected to the upper chamber (6) of the hydraulic cylinder (4). The hydraulic power source (1) is also connected to the pressure port P of the solenoid control valve (21). The working port A of the solenoid control valve (21) is connected to the return oil cartridge valve control chamber (18) of the return oil cartridge valve (17). The working port B of the solenoid control valve (21) is connected to the control port K of the differential control valve (16). The return oil port T of the solenoid control valve (21) is connected to the return oil tank (24).

2. The precision differential hydraulic control system for pile driving hammers according to claim 1, characterized in that: The control system includes at least two differential cartridge valves (11).

3. The precision differential hydraulic control system for pile driving hammers according to claim 2, characterized in that: The differential cartridge valve working chamber (14) of each differential cartridge valve (11) is connected to the lower chamber (5) of the hydraulic cylinder (4) after being connected in parallel. The differential cartridge valve annular chamber (13) of each differential cartridge valve (11) is connected to the upper chamber (6) of the hydraulic cylinder and the return oil cartridge valve working chamber (20) of the return oil cartridge valve (17) after being connected in series. The differential cartridge valve control chamber (12) of each differential cartridge valve (11) is connected to the pressure oil port P of the differential control valve (16).

4. The precision differential hydraulic control system for pile driving hammers according to claim 1, characterized in that: The upper chamber (6) of the hydraulic cylinder (4) is connected to the working chamber (20) of the return oil cartridge valve (17) via the annular chamber (13) of the differential cartridge valve (11).

5. The precision differential hydraulic control system for pile drivers according to claim 1, 2, 3 or 4, characterized in that: The lower chamber (5) of the hydraulic cylinder (4) is connected to the safety cartridge valve annular chamber (9) and the safety cartridge valve control chamber (8) of the safety cartridge valve (7), respectively. The working chamber (10) of the safety cartridge valve (7) is connected to the upper chamber (6) of the hydraulic cylinder and the differential cartridge valve annular chamber (13).

6. The precision differential hydraulic control system for pile driving hammers according to claim 1, characterized in that: The throttle valve (15) is an adjustable throttle valve or a fixed throttle valve.

7. The precision differential hydraulic control system for pile driving hammers according to claim 1, characterized in that: The differential control valve (16) is a normally open or normally closed two-position two-way hydraulic control valve.

8. The precision differential hydraulic control system for pile driving hammers according to claim 1, characterized in that: The electromagnetic control valve (21) is a two-position four-way electromagnetic valve.

9. The precision differential hydraulic control system for pile drivers according to claim 8, characterized in that: The electromagnetic control valve (21) is a two-position four-way dual-electro-controlled electromagnetic valve.

10. The precision differential hydraulic control system for pile driving hammers according to claim 1, characterized in that: The return port T of the electromagnetic control valve (21) is connected to the return tank (24) via the return check valve (22). The lower chamber (5) of the hydraulic cylinder is also connected to the inlet bypass accumulator (3). The return cartridge valve annular chamber (19) of the return cartridge valve (17) is connected to the return bypass accumulator (23).

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