JP4219464B2 - Piston pump switching shock reduction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulically driven piston pump used for pumping low slump concrete or earth and sand with poor fluidity in construction and civil engineering, or pumping low-water-content dehydrated sludge in sewage treatment plants and human waste treatment plants. The present invention relates to a switching impact reducing device.
[0002]
[Prior art]
In general, as shown in FIGS. 5 and 6, a hydraulically driven piston pump is provided with a pair of left and right suction discharge ports 1 </ b> L and 1 </ b> R at a lower portion of a back wall 1 </ b> B of a hopper 1. Pump cylinders 4L and 4R each having an open end are attached to 1L and 1R, respectively. The pump cylinders 4L and 4R are provided with transfer pistons 7L and 7R, respectively, and the transfer pistons 7L and 7R are reciprocated alternately by drive cylinders 6L and 6R. A water-sealed box 5 is provided at the joint between the pump cylinders 4L, 4R and the drive cylinders 6L, 6R.
[0003]
A rocking tube 2 is installed in the hopper 1. The oscillating tube 2 has a base end 2 </ b> B rotatably supported on the front wall 1 </ b> F of the hopper 1, and an intermediate portion of the oscillating tube 2 rotatably supported on the back wall 1 </ b> B of the hopper 1. One end of the oscillating tube shaft 10 is fixed. The rotation center of the oscillating tube shaft 10 and the rotation center of the base end portion 2B of the oscillating tube 2 are on the same line. A switching lever 11 is fixed to the other end of the oscillating tube shaft 10 extending outside the back wall 1B of the hopper 1, and switching cylinders 3L and 3R are attached between the switching lever 11 and the hopper 1. When one of the switching cylinders 3L and 3R expands, the other contracts.
[0004]
When the switching cylinders 3L and 3R expand and contract, the swing tube shaft 10 rotates, the swing tube 2 swings left and right, and the tip 2T of the swing tube 2 alternately turns to the left and right suction and discharge ports 1L and 1R. Move to the position where you face.
A replaceable sliding plate 8 provided with openings corresponding to the suction discharge ports 1L and 1R is attached to a portion where the tip 2T of the swing tube 2 around the suction discharge ports 1L and 1R of the hopper 1 is in sliding contact. ing. Moreover, since the front-end | tip part 2T of the rocking | fluctuation pipe | tube 2 is pressed and slid to the sliding plate 8, the replaceable wear ring 12 is attached. A wear resistant material is used for the sliding plate 8 and the wear ring 12.
[0005]
A transport pipe (not shown) is connected to the base end 2 </ b> B of the swing pipe 2.
When transporting objects such as earth and sand or dewatered sludge, the objects to be transported are put into the hopper 1. Accordingly, after one transport piston 7R (for example, the right side) is retracted and the object to be transported is sucked into the pump cylinder 4R, the swing pipe 2 is swung, and the tip 2T is sucked and discharged on the pump cylinder 4R side. At 1R, the transport piston 7R is advanced to discharge the transport object in the pump cylinder 4R from the swing pipe 2 to the transport pipe. When one pump cylinder 4R is in the discharge stroke, in the other pump cylinder 4L, the transport piston 7L is moved backward to suck the object to be transported into the pump cylinder 4L.
[0006]
Next, the oscillating tube 2 is oscillated so that the tip 2T faces the suction / discharge port 1L on the other pump cylinder 4L side, the transport piston 7L is advanced, and the object to be transported in the pump cylinder 4L is oscillated. 2 is discharged. The object to be transported is continuously transported by alternately performing the suction stroke and the discharge stroke on the left and right.
Conventionally, as shown in FIG. 7, the drive circuits of the drive cylinders 6L and 6R are configured such that the rod side oil chambers of the drive cylinders 6L and 6R are connected to each other through a communication pipe 21, and the head side oil of the drive cylinders 6L and 6R is connected. The chambers are connected to a variable displacement double swing hydraulic pump 33 through working lines 25L and 25R, respectively, to form a closed circuit. An auxiliary pump 32 is connected to the working lines 25L and 25R via check valves 31L and 31R. In addition, the working lines 25L and 25R are connected to the tank 24 via check valves 34L and 34R and relief valves 35 and 36.
[0007]
Further, proximity switches 30L, 30R are provided in the vicinity of the drive cylinders 6L, 6R in order to detect the stroke end of the discharge stroke of the drive pistons 9L, 9R, and the detection signals are sent to a control unit (not shown).
The head side oil chambers of the switching cylinders 3L and 3R are connected to the cylinder port of the swing control valve 27 through the left moving conduit 26L and the right moving conduit 26R, respectively, and the swing hydraulic pump is connected via the swing control valve 27. 28 and the tank 24.
[0008]
The swing control valve 27 is a two-position electromagnetic switching valve. By switching the swing control valve 27, the switching cylinders 3L and 3R are alternately expanded and contracted.
Above the switching cylinders 3L and 3R, a proximity switch 29L for detecting that the switching cylinder 3L is extended and the tip 2T of the swing pipe 2 has moved to a position facing the left suction / discharge port 1L and a switching cylinder 3R are provided. A proximity switch 29R that detects that the distal end portion 2T of the swing tube 2 has moved to a position facing the right suction / discharge port 1R is provided, and the detection signal is sent to the control unit.
[0009]
As shown in the figure, when one driving piston 9L reaches the stroke end of the discharge stroke and the other driving piston 9R reaches the stroke end of the suction stroke, the proximity switch 30L detects the arrival of the stroke end and sends the detection signal to the control unit. send.
Then, the control unit switches the swing control valve 27, expands the right switching cylinder 3R, shortens the left switching cylinder 3L, swings the swing tube 2 to the right, and moves the tip 2T to the right suction / discharge port. Let's face 1R. Therefore, the proximity switch 29R detects the arrival of the tip 2T of the oscillating tube 2 at the position facing the suction / discharge port 1R, and sends the detection signal to the controller.
[0010]
The control unit switches the discharge direction of the double swing hydraulic pump 33, extends the right drive cylinder 6R, shortens the left drive cylinder 6L, advances the transfer piston 7R, moves the transfer piston 7L backward, and transports it from the pump cylinder 4R. The object is discharged into the rocking tube 2, and the object to be transported is sucked from the hopper 1 into the pump cylinder 4L.
When the drive piston 9R reaches the stroke end of the discharge stroke and the drive piston 9L reaches the stroke end of the suction stroke, the proximity switch 30R detects arrival of the stroke end and sends a detection signal to the control unit.
[0011]
Then, the control section switches the swing control valve 27, shortens the right switching cylinder 3R, extends the left switching cylinder 3L, swings the swing pipe 2 to the left, and moves the tip 2T to the left suction / discharge. Let it face the exit 1L. Therefore, the proximity switch 29L detects the arrival of the tip 2T of the oscillating tube 2 at the position facing the suction / discharge port 1L, and sends the detection signal to the controller.
[0012]
The control unit switches the discharge direction of the double swing hydraulic pump 33, extends the left drive cylinder 6L, shortens the right drive cylinder 6R, advances the transfer piston 7L, retracts the transfer piston 7R, and transports it from the pump cylinder 4L. The object is discharged to the rocking tube 2, and the object to be transported is sucked from the hopper 1 into the pump cylinder 4R.
Thereafter, switching is controlled so that the suction and discharge strokes are alternately performed on the left and right.
[0013]
[Problems to be solved by the invention]
However, in this hydraulically driven piston pump, as shown in FIG. 8, the drive pistons 9L and 9R of the drive cylinders 6L and 6R reach the stroke end at the top speed, and the discharge pressures of the pump cylinders 4L and 4R are high. In this state, switching from the discharge stroke to the suction stroke has been performed, so a sudden change in discharge pressure from high pressure to low pressure may cause an impact during switching operation, or the pumping liquid in the transport pipe may flow backward. The phenomenon of doing has occurred.
[0014]
Therefore, the deceleration start position is set before the stroke end of the drive piston of the drive cylinder, a position command for deceleration command is provided, and the arrival of the drive piston to the deceleration start position is detected, thereby discharging the double swing hydraulic pump. A hydraulically driven piston pump has been proposed in which the amount of oil is controlled and the speed of the drive piston is reduced before switching from the discharge stroke to the suction stroke.
[0015]
However, in this hydraulically driven piston pump, if it is a liquid such as fresh water with good fluidity, as shown by a solid line in FIG. Can reduce the impact when switching from the suction stroke to the suction stroke and prevent backflow. However, in the case of dewatered sludge in a sewage treatment plant with poor fluidity, as shown by the broken line in FIG. The effect was not so great.
[0016]
An object of the present invention is to solve such a problem in a hydraulically driven piston pump, and to provide a switching impact reducing device for a piston pump capable of reducing impact at the time of switching between discharge and suction and preventing backflow. And
[0017]
[Means for Solving the Problems]
A piston pump switching impact reducing device according to the present invention includes a pump cylinder having one end opened at a suction / discharge port, a suction / discharge switching means at the suction / discharge port, a drive cylinder for driving a transfer piston of the pump cylinder, and an operation of the drive cylinder A hydraulically-driven piston pump having a variable displacement hydraulic pump connected to a pipeline, wherein a deceleration start position and a switching reference position are set before the stroke end of the drive piston of the drive cylinder, and each deceleration start position A detector and a switching reference position detector are provided, and after the arrival of the discharge stroke of the drive piston to the deceleration start position is detected, the amount of oil discharged from the variable displacement hydraulic pump is controlled to reduce the speed of the drive piston. The above-mentioned problem is achieved by switching the discharge suction after a predetermined decompression time has elapsed after detecting the arrival of the switching reference position. Solution to that.
[0018]
In the hydraulically driven piston pump, first, the suction / discharge port is switched to the suction side by the suction / discharge switching means, the transport piston is moved backward, and the object to be transported is sucked into the pump cylinder. Next, the suction / discharge port is switched to the discharge side by the suction / discharge switching means, the transport piston is moved forward, and the object to be transported in the pump cylinder is discharged from the suction / discharge port. The object to be transported is transported by alternately performing the suction and discharge strokes between the left and right pump cylinders.
[0019]
In this switching impact reducing device for a piston pump, the drive cylinder that drives the transfer piston as described above is provided with the deceleration start position detector and the switching reference position detector, and the drive piston in the discharge stroke is set at the deceleration start position. When it reaches, the amount of oil discharged from the variable displacement hydraulic pump is controlled to reduce the speed of the drive piston, and the drive piston further advances in the decelerated state and reaches the switching reference position. Switching from the post-discharge stroke to the suction stroke is performed.
[0020]
Therefore, the discharge pressure of the pump cylinder is sufficiently reduced at the time of switching between the discharge and the suction, the impact is reduced, and the backflow is prevented.
Pressure detection that sets the deceleration start position and the switching reference position before the stroke end of the driving piston of the driving cylinder and provides a deceleration starting position detector and a switching reference position detector, respectively, and detects the discharge pressure of the pump cylinder After detecting the arrival of the drive piston to the deceleration start position in the discharge stroke, the amount of oil discharged from the variable displacement hydraulic pump is controlled to reduce the speed of the drive piston, and the drive piston reaches the switching reference position. If it is configured to detect and reduce the discharge pressure of the pump cylinder to the specified pressure, and then switch the discharge suction, the discharge pressure of the pump cylinder can be reduced to a more appropriate pressure when switching the discharge suction. Impact is reduced and backflow is prevented.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a hydraulic circuit diagram showing a configuration of a switching impact reducing device for a hydraulically driven piston pump according to an embodiment of the present invention.
Here, the structure of the piston pump itself is a double cylinder type piston pump similar to the piston pump shown in FIGS. 5 and 6, and a pair of left and right suction / discharge ports 1 </ b> L and 1 </ b> R are provided in the lower part of the back wall 1 </ b> B of the hopper 1. On the back of the hopper 1, pump cylinders 4L and 4R each having one end opened to the suction and discharge ports 1L and 1R are attached. The pump cylinders 4L and 4R are provided with transfer pistons 7L and 7R, respectively, and the transfer pistons 7L and 7R are reciprocated alternately by drive cylinders 6L and 6R. A water-sealed box 5 is provided at the joint between the 4L and 4R and the drive cylinders 6L and 6R.
[0022]
A rocking tube 2 is installed in the hopper 1. The oscillating tube 2 has a base end 2 </ b> B rotatably supported on the front wall 1 </ b> F of the hopper 1, and an intermediate portion of the oscillating tube 2 rotatably supported on the back wall 1 </ b> B of the hopper 1. One end of the oscillating tube shaft 10 is fixed. The rotation center of the oscillating tube shaft 10 and the rotation center of the base end portion 2B of the oscillating tube 2 are on the same line. A switching lever 11 is fixed to the other end of the oscillating tube shaft 10 extending outside the back wall 1B of the hopper 1, and switching cylinders 3L and 3R are attached between the switching lever 11 and the hopper 1. When one of the switching cylinders 3L, 3R expands, the other contracts.
[0023]
When the switching cylinders 3L and 3R expand and contract, the swing tube shaft 10 rotates, the swing tube 2 swings left and right, and the tip 2T of the swing tube 2 alternately turns to the left and right suction and discharge ports 1L and 1R. Move to the position where you face.
A replaceable sliding plate 8 provided with openings corresponding to the suction discharge ports 1L and 1R is attached to a portion where the tip 2T of the swing tube 2 around the suction discharge ports 1L and 1R of the hopper 1 is in sliding contact. ing. Moreover, since the front-end | tip part 2T of the rocking | fluctuation pipe | tube 2 is pressed and slid to the sliding plate 8, the replaceable wear ring 12 is attached. A wear resistant material is used for the sliding plate 8 and the wear ring 12.
[0024]
A transport pipe (not shown) is connected to the base end 2 </ b> B of the swing pipe 2.
When transporting a transport object such as earth and sand, the transport object is put into the hopper 1. Accordingly, after one transport piston 7R (for example, the right side) is retracted and the object to be transported is sucked into the pump cylinder 4R, the swing pipe 2 is swung, and the tip 2T is sucked and discharged on the pump cylinder 4R side. At 1R, the transport piston 7R is advanced to discharge the transport object in the pump cylinder 4R from the swing pipe 2 to the transport pipe. When one pump cylinder 4R is in the discharge stroke, in the other pump cylinder 4L, the transport piston 7L is moved backward to suck the object to be transported into the pump cylinder 4L.
[0025]
Next, the oscillating tube 2 is oscillated so that the tip 2T faces the suction / discharge port 1L on the other pump cylinder 4L side, the transport piston 7 is advanced, and the object to be transported in the pump cylinder 4L is oscillated. 2 is discharged. The object to be transported is continuously transported by alternately performing the suction stroke and the discharge stroke on the left and right.
As shown in FIG. 1, in the drive circuit of this piston pump, the rod side oil chambers of the drive cylinders 6L and 6R are connected to each other by a communication pipe 21, and the head side oil chambers of the drive cylinders 6L and 6R are operated. The lines 25L and 25R are connected to a variable displacement double swing hydraulic pump 33 to form a closed circuit. An auxiliary pump 32 is connected to the working lines 25L and 25R via check valves 31L and 31R. In addition, the working lines 25L and 25R are connected to the tank 24 via check valves 34L and 34R and relief valves 35 and 36.
[0026]
The head side oil chambers of the switching cylinders 3L and 3R are connected to the cylinder port of the swing control valve 27 through the left moving conduit 26L and the right moving conduit 26R, respectively, and the swing hydraulic pump is connected via the swing control valve 27. 28 and the tank 24.
The swing control valve 27 is a two-position electromagnetic switching valve. By switching the swing control valve 27, the switching cylinders 3L and 3R are alternately expanded and contracted.
[0027]
The drive cylinders 6L and 6R are provided with deceleration start position detectors 41L and 41R and a switching reference position detector at a deceleration start position and a switching reference position set before the forward stroke end of the drive pistons 9L and 9R. 42L and 42R are provided. The deceleration start position detectors 41L and 41R and the switching reference position detectors 42L and 42R are proximity switches that detect the proximity of the head portions of the drive pistons 9L and 9R, and the deceleration start position detectors 41L and 41R are discharge strokes. When the arrival of the drive pistons 9L and 9R to the deceleration start position is detected, a detection signal is sent to a control unit (not shown). The control unit controls the double swing hydraulic pump 33 to reduce the amount of discharged oil and decelerate the speeds of the drive pistons 9L and 9R.
[0028]
When the switching reference position detectors 42L and 42R detect the arrival of the drive pistons 9L and 9R at the switching reference position, the detection reference signals are sent to the control unit. The control unit causes the discharge stroke to be switched to the suction stroke after a predetermined decompression time has elapsed after the drive pistons 9L and 9R reach the switching reference position.
Above the switching cylinders 3L and 3R, a switching position detector 29L that detects that the switching cylinder 3L has extended and the tip 2T of the swing tube 2 has moved to a position facing the left suction / discharge port 1L, and a switching cylinder There is provided a switching position detector 29R that detects that 3R extends and the tip 2T of the swing tube 2 has moved to a position facing the right suction / discharge port 1R. The switching position detectors 29L and 29R are proximity switches, and send detection signals to the control unit. Based on the detection signal, the control unit switches the discharge direction of the double swing hydraulic pump 33 in the reverse direction and moves the drive pistons 9L and 9R in the reverse direction.
[0029]
When the drive piston 9 of the left drive cylinder 6L moves forward and reaches the deceleration start position in the discharge stroke of the left pump cylinder 4L, the deceleration start position detector 41L detects the arrival of the drive piston at the 9L deceleration start position. Then, the swing hydraulic pump 33 is controlled to reduce the forward speed of the drive piston 9L and the reverse speed of the drive piston 9R.
When the speed of the drive piston 9L is decelerated, the discharge pressure of the pump cylinder 4L decreases as shown in FIG.
[0030]
When the driving piston further advances in the state of 9L deceleration and reaches the switching reference position, the switching reference position detector 42L detects the arrival of the driving piston at the switching reference position of 9L. The controller switches the swing control valve 27 to shorten the left switching cylinder 3L, expands the right switching cylinder 3R, swings the swing pipe 2 to the right, and moves the tip 2T to the right suction / discharge port. Let's face 1R.
[0031]
Therefore, the switching position detector 29R detects the arrival of the tip 2T of the oscillating tube 2 at the position facing the suction / discharge port 1R, and switches the discharge direction of the double swing hydraulic pump 33 in the reverse direction to switch the drive piston 9L. The drive piston 9R is moved backward, and the discharge stroke of the right pump cylinder 4R, that is, the forward travel stroke of the right drive cylinder 6R is entered.
The depressurization time when switching from the discharge stroke to the suction stroke is a time required for sufficient depressurization as shown in FIG. 2 so as not to cause an impact at the time of switching according to the properties of the object to be transported. Is set.
[0032]
Therefore, the discharge pressure of the pump cylinder 4L is sufficiently reduced at the time of switching between the discharge and the suction, and the impact is reduced and the backflow is prevented.
The same control is performed when the right drive piston 9R reaches the deceleration start position and the switching reference position, and thereafter, the suction and discharge strokes are alternately repeated on the left and right.
[0033]
FIG. 3 is a hydraulic circuit diagram showing another embodiment of the present invention.
In the piston pump impact reducing device of FIG. 3, a pressure detector 38 for detecting the discharge pressure of the pump cylinders 4L, 4R is provided. Other circuit configurations are the same as those in FIG.
In the discharge stroke of the pump cylinder 41L, when the drive piston 9L reaches the deceleration start position, the deceleration start position detector 41L detects the arrival of the drive piston 9L to the deceleration position and controls the amount of oil discharged from the double swing hydraulic pump 33. Thus, the forward speed of the drive piston 9L is decelerated.
[0034]
When the driving piston 9L further moves forward and reaches the switching device reference position, the switching reference position detector 42L detects the arrival of the driving piston 9L to the switching reference position. As shown in FIG. 4, the control unit switches the discharge suction after the pressure detector 38 detects that the discharge pressure of the pump cylinder 4L has been reduced to a predetermined pressure.
At the time of switching between discharge and suction, the discharge pressure of the pump cylinder 4L can be reduced to a more appropriate pressure, so that the impact is reduced more effectively and backflow is prevented.
[0035]
The same control is performed when the right drive piston 9R reaches the deceleration start position and the switching reference position, and the suction and discharge strokes are alternately repeated on the left and right.
The piston pump of FIGS. 1 and 3 uses the double swing hydraulic pump 33, but a variable displacement pump other than the double swing hydraulic pump 33 can be used. In that case, a direction switching valve is provided in the working pipeline so as to switch the supply direction of the discharge oil.
[0036]
【The invention's effect】
As described above, the impact reducing device for a piston pump according to the present invention can reduce impact at the time of switching between discharge and suction and prevent backflow in a hydraulically driven piston pump.
Pressure detection that sets the deceleration start position and the switching reference position before the stroke end of the driving piston of the driving cylinder and provides a deceleration starting position detector and a switching reference position detector, respectively, and detects the discharge pressure of the pump cylinder After detecting the arrival of the drive piston to the deceleration start position in the discharge stroke, the amount of oil discharged from the variable displacement hydraulic pump is controlled to reduce the speed of the drive piston, and the drive piston reaches the switching reference position. Detecting and detecting the pressure reduction of the discharge pressure of the pump cylinder to the predetermined pressure, and switching the discharge suction, the discharge pressure of the pump cylinder can be reduced to a more appropriate pressure at the time of discharge suction switching. Impact is reduced and backflow is prevented.
[Brief description of the drawings]
FIG. 1 is a hydraulic circuit diagram showing a configuration of a switching impact reducing device for a hydraulically driven piston pump according to an embodiment of the present invention.
FIG. 2 is an explanatory view of a change in discharge pressure at the time of switching between discharge and suction of the switching impact reducing device for a piston pump in FIG. 1;
FIG. 3 is a hydraulic circuit diagram showing another embodiment of the present invention.
4 is an explanatory diagram of a change in discharge pressure when switching between discharge and suction in the piston pump switching impact reduction device of FIG. 3; FIG.
FIG. 5 is a plan view of a conventional piston pump.
FIG. 6 is a longitudinal sectional view taken along the center of a swing pipe of a hopper portion of a conventional piston pump.
FIG. 7 is a hydraulic circuit diagram of a conventional hydraulically driven piston pump.
FIG. 8 is an explanatory diagram of a change in discharge pressure when switching between discharge and suction of a conventional hydraulically driven piston pump.
FIG. 9 is an explanatory diagram of a change in discharge pressure when switching between discharge and suction of a conventional hydraulically driven piston pump.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hopper 2 Oscillation pipe 1L, 1R Suction discharge port 3L, 3R Switching cylinder 4L, 4R Pump cylinder 6L, 6R Drive cylinder 7L, 7R Transfer piston 9L, 9R Drive piston 10 Oscillation pipe shaft 11 Switching lever 21 Communication pipe line 25L , 25R Working line 26L Left moving line 26R Right moving line 27 Swing control valve 28 Swing hydraulic pump 29L, 29R Switching position detector 33 Double swing hydraulic pump 38 Pressure detector 41L, 41R Deceleration start position detector 42L 42R switching reference position detector

Claims (2)

A pump cylinder having one end opened at the suction discharge port, a suction / discharge switching means of the suction discharge port, a drive cylinder for driving a transfer piston of the pump cylinder, and a variable displacement hydraulic pump to which an operation line of the drive cylinder is connected In a hydraulically driven piston pump with
A deceleration start position and a switching reference position are set before the stroke end of the driving piston of the driving cylinder, and a deceleration starting position detector and a switching reference position detector are provided, respectively, to the deceleration starting position of the driving piston in the discharge stroke. After detecting the arrival of, the discharge volume of the variable displacement hydraulic pump is controlled to decelerate the speed of the drive piston, and after the depressurization time has elapsed since the arrival of the drive piston to the switching reference position, the discharge suction is switched. A switching impact reducing device for a piston pump, characterized in that A pump cylinder having one end opened at the suction discharge port, a suction / discharge switching means of the suction discharge port, a drive cylinder for driving a transfer piston of the pump cylinder, and a variable displacement hydraulic pump to which an operation line of the drive cylinder is connected In a hydraulically driven piston pump with
Pressure for setting the deceleration start position and the switching reference position before the stroke end of the driving piston of the driving cylinder, providing a deceleration starting position detector and a switching reference position detector, respectively, and detecting the discharge pressure of the pump cylinder A detector is provided to detect the arrival of the drive piston at the deceleration start position in the discharge stroke, and then control the amount of oil discharged from the variable displacement hydraulic pump to reduce the speed of the drive piston so that the drive piston reaches the switching reference position. And a switching shock reduction device for a piston pump, wherein the discharge suction is switched after detecting the pressure reduction of the discharge pressure of the pump cylinder to a predetermined pressure.

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