An electrically controlled load-sensitive pump source with constant pressure function and a control method

Abstract

The application discloses a kind of electrically controlled load-sensitive pump sources with constant voltage function, including motor, electronic pressure and flow control electro-hydraulic proportional variable pump, safety overflow valve, proportional speed regulating valve, first pressure sensor, second pressure sensor, third pressure sensor, differential pressure controller and host computer;The oil suction port of electro-hydraulic proportional variable pump is communicated with oil tank, the input end of electro-hydraulic proportional variable pump is connected with motor, and pump control controller, swash plate, proportional reversing valve and swing angle sensor are integrated in electro-hydraulic proportional variable pump, and pressure PID adjusting module and displacement PID adjusting module are integrated in pump control controller;Pump source has constant voltage control mode, constant voltage proportional flow control mode, proportional flow control mode and load-sensitive control mode.The application solves the pressure oscillation caused by traditional mechanical LS feedback oil circuit, response lag, saves damping hole, blind tube trial and error debugging, can realize the undisturbed switching of multiple working modes, and is suitable for a variety of hydraulic valve factory test.

Description

Technical Field

[0001] This invention relates to the field of hydraulic valve testing equipment technology, specifically to an electro-hydraulic pump source and its control method that integrates constant pressure control and load sensitivity functions for use on a hydraulic valve factory test bench. Background Technology

[0002] In the factory testing of hydraulic valves, it is usually necessary to test items such as internal leakage, steady-state pressure-flow characteristics, and constant pressure drop flow characteristics for relief valves, pressure reducing valves, proportional directional valves, and multi-way valves. These tests require the test bench pump source to have multiple operating modes, including constant pressure control, proportional flow control, constant pressure proportional flow control, and load-sensitive control, and to be able to remotely adjust the pump source output pressure differential according to the pressure differential at the valve port of the valve under test.

[0003] In existing technologies, traditional load-sensitive pumps are often used as the power source, supplemented by complex hydraulic valve assemblies to achieve multi-mode switching. However, the structure of traditional load-sensitive pumps dictates that they must rely on long external LS (Load Sensing) feedback oil circuits and P-port feedback oil circuits. This long pipeline layout significantly increases the system cavity, making it prone to problems such as response lag, pressure overshoot, and high-frequency vibration during operating condition switching.

[0004] To address the aforementioned issues, the industry standard approach is to add a damping orifice to the feedback pipeline or connect a blind pipe before the control chamber of the LS control valve to increase system damping and suppress pressure fluctuations. While this method can alleviate pressure fluctuations to some extent, it essentially comes at the cost of sacrificing the system's dynamic response speed. Furthermore, different specifications of the tested valves have varying requirements for damping characteristics, and there is a lack of mature engineering formulas for calculating the diameter of the damping orifice and the length of the blind pipe. The process relies heavily on trial and error, which significantly increases test preparation time and operational complexity, limiting the versatility and automation level of the test bench.

[0005] Therefore, there is an urgent need for a hydraulic test bench pump source that can overcome the above-mentioned defects. Summary of the Invention

[0006] The purpose of this invention is to provide an electrically controlled load-sensitive pump source and control method with constant pressure function, which solves the pressure oscillation and response lag caused by traditional mechanical LS feedback oil circuit, eliminates the need for damping orifice and blind pipe trial and adjustment, can realize seamless switching of multiple working modes, and is compatible with the factory test of various hydraulic valves.

[0007] The technical solution of the present invention is as follows: an electrically controlled load-sensitive pump source with constant pressure function, including a motor, an electro-hydraulic proportional variable pump with electronic pressure and flow control, a safety relief valve, a proportional speed control valve, a first pressure sensor, a second pressure sensor, a third pressure sensor, a flow meter, a differential pressure controller, and a host computer.

[0008] The suction port of the electro-hydraulic proportional variable pump is connected to the oil tank, and the input end of the electro-hydraulic proportional variable pump is connected to the motor. The electro-hydraulic proportional variable pump integrates a pump control controller, a swashplate, a proportional reversing valve for driving the swashplate, and a swing angle sensor for detecting the swashplate angle.

[0009] The main outlet oil circuit of the electro-hydraulic proportional variable pump is divided into two paths: one path is connected to the oil inlet of the safety relief valve, and the other path is connected to the oil inlet of the proportional speed control valve; the oil outlet of the safety relief valve is connected to the oil tank, and the maximum safe working pressure of the system is set through the safety relief valve.

[0010] The first pressure sensor is installed at the outlet of the electro-hydraulic proportional variable pump to collect the pump source outlet pressure Pp. The signal output terminal of the first pressure sensor is connected to the pump control controller and forms a constant pressure closed loop with the pressure PID module inside the pump control controller.

[0011] The outlet of the proportional speed control valve is connected to the inlet of the valve under test.

[0012] The second pressure sensor is installed at the oil inlet of the valve under test to collect pressure P1, and the third pressure sensor is installed at the load port of the valve under test to collect pressure P2. The P1 and P2 signals are input to the differential pressure controller.

[0013] The flow meter is installed at the outlet of the proportional speed control valve, and the signal output terminal of the flow meter is connected to the signal input terminal of the differential pressure controller.

[0014] The differential pressure controller is connected to the host computer for communication. The output of the differential pressure controller is connected to the control terminal of the proportional speed control valve and the command input terminal of the pump control controller, respectively.

[0015] The pump source has multiple operating modes, including constant pressure control mode, constant pressure proportional flow control mode, proportional flow control mode and load-sensitive control mode.

[0016] In the aforementioned electrically controlled load-sensitive pump source with constant pressure function, the pump control controller integrates a pressure PID adjustment module and a displacement PID adjustment module. In constant pressure control mode, the pump source outlet pressure Pp collected by the first pressure sensor is used as the feedback value, and is input to the pump control controller together with the target pressure value issued by the differential pressure controller. The pressure PID adjustment module adjusts the pump displacement through the proportional reversing valve to stabilize Pp at the target value.

[0017] In the aforementioned electrically controlled load-sensitive pump source with constant pressure function, under constant pressure proportional flow control mode, the differential pressure controller sends a target pressure command to the pump control controller (4) to maintain a constant pump source outlet pressure; and adjusts the opening of the proportional speed control valve according to the real-time flow feedback collected by the flow meter to achieve precise control of the output flow.

[0018] In the aforementioned electrically controlled load-sensitive pump source with constant pressure function, under load-sensitive control mode, the differential pressure controller calculates the pressure difference ΔP=P1-P2 across the valve under test, uses a PID algorithm to process the real-time pressure difference ΔP, and outputs a displacement adjustment signal to the pump control controller. The pump control controller calls the displacement PID adjustment module to drive the proportional directional valve (3) to adjust the swashplate angle of the electro-hydraulic proportional variable pump (1) so that the pressure difference across the valve under test remains constant, thereby ensuring the stable flow rate through the valve under test.

[0019] In the aforementioned electrically controlled load-sensitive pump source with constant pressure function, in the proportional flow control mode, the differential pressure controller inputs the maximum pressure limit signal and the target displacement signal to the pump control controller, and at the same time inputs the full-open control signal to the proportional speed control valve, so that the valve port of the proportional speed control valve maintains the maximum opening.

[0020] Based on the target displacement signal and feedback from the swashplate sensor, the pump controller calls the displacement PID adjustment module to drive the proportional directional valve to adjust the swashplate tilt angle, thereby directly controlling the pump source output flow and realizing pump-controlled proportional flow regulation.

[0021] In the aforementioned electrically controlled load-sensitive pump source with constant pressure function, the pump source eliminates the external mechanical connection of the LS feedback oil circuit and the P port feedback oil circuit, and transmits differential pressure information through electronic signals, eliminating the need to set up damping orifices or blind pipes in the oil circuit to suppress vibration.

[0022] The aforementioned control method for an electronically controlled load-sensitive pump source with constant pressure function includes the following steps:

[0023] a. The system performs a power-on self-test, and the target working mode is selected and the corresponding target parameters are entered through the host computer;

[0024] b. If constant pressure control mode is selected, the differential pressure calculation logic and flow calculation logic of the differential pressure controller are disabled; the differential pressure controller receives the target pressure command sent by the host computer and sends the target pressure command to the pump control controller. The pump control controller collects the pressure feedback signal detected by the first pressure sensor in real time, calls the internal pressure PID adjustment module to perform closed-loop calculation, drives the proportional directional valve to act according to the calculation result, adjusts the swashplate angle of the electro-hydraulic proportional variable pump to change the pump output displacement, dynamically compensates for system pressure fluctuations, and finally maintains the pump source outlet pressure constant.

[0025] c. If the constant pressure proportional flow control mode is selected, the differential pressure calculation logic of the differential pressure controller is disabled; while the differential pressure controller sends the target pressure command to maintain the constant pump source outlet pressure, it adjusts the opening of the proportional speed control valve according to the real-time flow feedback from the flow meter to control the output flow.

[0026] d. If the proportional flow control mode is selected, the differential pressure calculation logic of the differential pressure controller is disabled; the maximum pressure limit signal and the target displacement signal are input to the pump control controller, and a full-open control signal is input to the proportional speed control valve at the same time, so that the valve port of the proportional speed control valve is kept at the maximum opening; the pump control controller drives the proportional reversing valve to adjust the pump swashplate tilt angle according to the target displacement signal and the feedback of the swashplate tilt sensor, thereby directly controlling the pump source output flow and realizing pump control proportional flow regulation;

[0027] e. If the load-sensitive control mode is selected, the flow calculation logic of the differential pressure controller is disabled; the differential pressure controller calculates the real-time differential pressure ΔP=P1-P2 across the valve under test, compares ΔP with the target differential pressure ΔPref, and outputs a discharge adjustment signal to the pump control controller so that the differential pressure across the valve under test tracks the target differential pressure ΔPref.

[0028] Compared with the prior art, the beneficial results of the present invention are as follows:

[0029] (1) The traditional load-sensitive pump relies on the mechanical feedback method of external LS pipeline and P pipeline, and uses electronic signal to transmit pressure difference information. This eliminates pressure oscillation and response lag caused by pipeline cavity, and eliminates the need to install damping holes and blind pipes, thus solving the problem of trial and error debugging.

[0030] (2) By utilizing the built-in pump controller of the electro-hydraulic proportional variable pump and the differential pressure control signal to form an electronic closed loop, the signal transmission has almost no delay, and the system response speed is significantly improved.

[0031] (3) The software logic can switch between constant pressure, constant pressure proportional flow, proportional flow and load sensitive working modes without replacing the hardware pipeline, and can adapt to the factory test requirements of different types and different diameter hydraulic valves.

[0032] (4) During the test, the above-mentioned pump source can be stably switched between constant pressure control mode, constant pressure proportional flow control mode, proportional flow control mode and load sensitive control mode; thus enabling the test bench to be compatible with the testing of various hydraulic valves such as relief valve, pressure reducing valve, proportional directional valve, multi-way valve, etc., and to realize the factory test of hydraulic valves simply and efficiently.

[0033] (5) When the pump source is operating under constant pressure proportional flow control, the output flow of the pump source can be steplessly adjusted from zero flow to maximum flow by adjusting the proportional speed control valve.

[0034] (6) Since the working differential pressure of the hydraulic valve is not unique, different products may require adjustment of the spring of the constant flow valve of the load-sensitive pump, which is inconvenient. The above-mentioned pump source forms a closed loop with the electro-hydraulic proportional variable pump through the differential pressure signal to keep the differential pressure across the valve under test constant. When it is necessary to change the differential pressure, the differential pressure of the load-sensitive variable pump can be easily adjusted. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the present invention.

[0036] The labels in the attached diagram are as follows: 1-Electro-hydraulic proportional variable pump; 2-Swing angle sensor; 3-Proportional directional valve; 4-Pump control controller; 5-Host computer; 6-Differential pressure controller; 7-Second pressure sensor; 8-Third pressure sensor; 9-Flow meter; 10-Proportional speed control valve; 11-Safety relief valve; 12-Motor; 13-First pressure sensor. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0038] Example: An electronically controlled load-sensitive pump source with constant pressure function, such as... Figure 1 As shown, it includes a motor 12, an electro-hydraulic proportional variable pump 1 with electronic pressure and flow control, a safety relief valve 11, a proportional speed control valve 10, a first pressure sensor 13, a second pressure sensor 7, a third pressure sensor 8, a differential pressure controller 6, and a host computer 5.

[0039] The electro-hydraulic proportional variable pump 1 with electronic pressure and flow control is model A4VSO71DFE1; the host computer 5 is model IPC610-LFSP500W-AIMB76G2; the differential pressure controller 6 is model S7-1500 CPU1511C-1 PN; the second pressure sensor 7, the third pressure sensor 8, and the first pressure sensor 13 are models P-30-P-BG560-HDZZ-F-A4Z-ZZ; the proportional speed control valve 10 is model 2FRE16-4X / 125LBK4; and the safety relief valve is model DBW10B15X / 350Y. These models are for illustrative purposes only and do not represent the only available options.

[0040] The electro-hydraulic proportional variable pump 1 has its suction port connected to the oil tank, and its input end connected to the motor 12, which drives its operation. The electro-hydraulic proportional variable pump 1 integrates a pump control controller 4, a swashplate, a proportional directional valve 3 for driving the swashplate, and a swashplate angle sensor 2 for detecting the swashplate angle. The proportional directional valve 3 drives the swashplate, changing its swashplate angle and thus the pump's displacement. The pump control controller 4 integrates a pressure PID control module and a displacement PID control module.

[0041] The main outlet oil circuit of the electro-hydraulic proportional variable pump 1 is divided into two paths: one path connects to the inlet of the safety relief valve 11, and the other path connects to the inlet of the proportional speed control valve 10. The outlet of the safety relief valve 11 is connected to the oil tank and is used to set the maximum safe operating pressure of the system.

[0042] The first pressure sensor 13 is located at the outlet of the electro-hydraulic proportional variable pump 1 and is used to collect the pump source outlet pressure Pp. Its signal output terminal is connected to the pump control controller 4 and forms a constant pressure closed loop with the pressure PID module inside the pump control controller 4.

[0043] The outlet of the proportional speed control valve 10 is connected to the inlet of the valve under test. The second pressure sensor 7 is installed at the inlet of the valve under test to collect pressure P1; the third pressure sensor 8 is installed at the load port (A / B port) of the valve under test to collect pressure P2. Both the second pressure sensor 7 and the third pressure sensor 8 are connected to the differential pressure controller 6, and the P1 and P2 signals are input to the differential pressure controller 6.

[0044] The flow meter 9 is installed at the outlet of the proportional speed control valve 10, and its output signal is connected to the input of the differential pressure controller 6.

[0045] The differential pressure controller 6 is connected to the host computer 5 via communication. The output terminals of the differential pressure controller 6 are connected to the control terminal of the proportional speed control valve 10 and the command input terminal of the pump control controller 4, respectively.

[0046] This embodiment of the electronically controlled load-sensitive pump source control method with constant pressure function includes the following control:

[0047] After the system is powered on, the host computer 5 sends mode commands and target parameters to the differential pressure controller according to the operating mode set in the test process. The differential pressure controller executes different calculation strategies according to the current mode and outputs control signals. There are four operating modes: constant pressure control mode, constant pressure proportional flow control mode, proportional flow control mode, and load-sensitive control mode, as detailed below:

[0048] Constant pressure control mode: Suitable for tests such as internal leakage testing of hydraulic valves. The host computer 5 sets the target pressure Ppref, and disables the differential pressure controller 6's differential pressure calculation logic and flow calculation logic. The differential pressure controller 6 receives the target pressure command from the host computer 5 and sends the target pressure command: Ppref signal to the pump control controller 4. The pump control controller 4 collects the pressure feedback signal detected by the first pressure sensor 13 in real time, calls the internal pressure PID adjustment module to perform closed-loop calculation, and drives the proportional directional valve 3 to act according to the calculation result, adjusting the swashplate angle of the electro-hydraulic proportional variable pump 1 to change the pump output displacement, dynamically compensating for system pressure fluctuations, and finally maintaining a constant pump source outlet pressure, so that Pp collected by the first pressure sensor 13 is equal to Ppref.

[0049] Constant pressure proportional flow control mode: suitable for hydraulic valve tests requiring constant pressure and flow. The host computer 5 sets the target pressure Ppref and target flow rate Qref. The differential pressure controller 6 sends Ppref to the pump control controller 4 to maintain a constant pump outlet pressure; on the other hand, it starts the flow PID calculation, and adjusts the opening of the proportional speed control valve 10 according to the deviation between the actual flow rate Q collected by the flow meter 9 and the target flow rate Qref, so as to accurately control the output flow rate.

[0050] Proportional flow control mode: Suitable for test conditions that require precise flow control and do not require constant pressure. The host computer sets the maximum pressure limit value Pmax and the target displacement Qref. The differential pressure controller 6 sends Pmax to the pump control controller 4 as a safety pressure limit; at the same time, it outputs a fully open signal to the proportional speed control valve 10 to eliminate throttling losses. The pump control controller (4) receives the target displacement signal, combines it with the position feedback of the swashplate sensor (2), calls the displacement PID adjustment module to drive the proportional reversing valve 3, changes the pump swashplate tilt angle, and directly realizes precise proportional adjustment of the pump source output flow.

[0051] Load-sensitive control mode: Applicable to valve flow characteristic tests of multi-way valves and proportional valves. The host computer 5 sets the target differential pressure ΔPref. The differential pressure controller 6 calculates ΔP = P1 - P2 in real time. A displacement request signal is output to the pump controller 4 via PID calculation. The pump controller 4 calls the displacement PID adjustment module to drive the proportional directional valve 3 to change the swashplate angle, ensuring that the differential pressure ΔP across the valve under test always follows the target differential pressure ΔPref; when the load changes, the differential pressure across the valve under test remains constant, and the flow rate through the valve remains stable.

[0052] During the experiment, without stopping the motor, the present invention can seamlessly switch the pump source between constant pressure control mode, constant pressure proportional flow control mode, load sensitive control mode and proportional flow control mode according to different test items, and accurately and quickly provide the flow and pressure required for the test.

[0053] The shielding operation logic described in this invention refers to shutting down the operation output of the corresponding algorithm module inside the differential pressure controller software, not cutting off the sensor signal input in hardware.

Claims

1. An electrically controlled load-sensitive pump source with constant pressure function, characterized in that: Includes a motor (12), an electro-hydraulic proportional variable pump (1) with electronic pressure and flow control, a safety relief valve (11), a proportional speed control valve (10), a first pressure sensor (13), a second pressure sensor (7), a third pressure sensor (8), a flow meter (9), a differential pressure controller (6), and a host computer (5). The oil inlet of the electro-hydraulic proportional variable pump (1) is connected to the oil tank, and the input end of the electro-hydraulic proportional variable pump (1) is connected to the motor (12). The electro-hydraulic proportional variable pump (1) integrates a pump control controller (4), a swashplate, a proportional reversing valve (3) for driving the swashplate, and a swing angle sensor (2) for detecting the angle of the swashplate. The main oil circuit of the electro-hydraulic proportional variable pump (1) is divided into two circuits: one circuit is connected to the oil inlet of the safety relief valve (11), and the other circuit is connected to the oil inlet of the proportional speed control valve (10); the oil outlet of the safety relief valve (11) is connected to the oil tank, and the maximum safe working pressure of the system is set through the safety relief valve (11). The first pressure sensor (13) is set at the outlet of the electro-hydraulic proportional variable pump (1) to collect the pump source outlet pressure Pp. The signal output terminal of the first pressure sensor (13) is connected to the pump control controller (4) and forms a constant pressure closed loop with the pressure PID module inside the pump control controller (4). The outlet of the proportional speed control valve (10) is connected to the inlet of the valve under test; The second pressure sensor (7) is set at the oil inlet of the valve under test to collect pressure P1, and the third pressure sensor (8) is set at the load port of the valve under test to collect pressure P2. The P1 and P2 signals are input to the differential pressure controller (6). The flow meter (9) is installed at the outlet of the proportional speed control valve (10), and the signal output terminal of the flow meter (9) is connected to the signal input terminal of the differential pressure controller (6); The differential pressure controller (6) is connected to the host computer (5) for communication. The output terminal of the differential pressure controller (6) is connected to the control terminal of the proportional speed control valve (10) and the instruction input terminal of the pump control controller (4). The pump source has multiple operating modes, including constant pressure control mode, constant pressure proportional flow control mode, proportional flow control mode and load-sensitive control mode.

2. The electrically controlled load-sensitive pump source with constant pressure function according to claim 1, characterized in that: The pump controller (4) integrates a pressure PID adjustment module and a displacement PID adjustment module. In constant pressure control mode, the pump source outlet pressure Pp collected by the first pressure sensor (13) is used as the feedback value and input to the pump controller (4) together with the target pressure value issued by the differential pressure controller (6). The pressure PID adjustment module adjusts the pump displacement through the proportional reversing valve (3) to stabilize Pp at the target value.

3. The electrically controlled load-sensitive pump source with constant pressure function according to claim 1, characterized in that: In constant pressure proportional flow control mode, the differential pressure controller (6) sends the target pressure command to the pump control controller (4) to maintain the constant pump source outlet pressure; and adjusts the opening of the proportional speed control valve (10) according to the real-time flow feedback collected by the flow meter (9) to achieve precise control of the output flow.

4. The electrically controlled load-sensitive pump source with constant pressure function according to claim 1, characterized in that: In the load-sensitive control mode, the differential pressure controller (6) calculates the pressure difference ΔP = P1 - P2 across the valve under test, uses the PID algorithm to process the real-time pressure difference ΔP, and outputs the displacement adjustment signal to the pump control controller (4). The pump control controller (4) calls the displacement PID adjustment module to drive the proportional directional valve (3) to adjust the swashplate angle of the electro-hydraulic proportional variable pump (1) so that the pressure difference across the valve under test remains constant, thereby ensuring the flow rate through the valve under test is stable.

5. The electrically controlled load-sensitive pump source with constant pressure function according to claim 1, characterized in that: In the proportional flow control mode, the differential pressure controller (6) inputs the maximum pressure limit signal and the target discharge signal to the pump control controller (4), and simultaneously inputs the full-open control signal to the proportional speed control valve (10) so that the valve port of the proportional speed control valve (10) is kept at the maximum opening. The pump controller (4) calls the displacement PID adjustment module to drive the proportional directional valve (3) to adjust the swashplate tilt angle based on the target displacement signal and feedback from the swashplate sensor (2), thereby directly controlling the pump source output flow and realizing pump control proportional flow regulation.

6. The electrically controlled load-sensitive pump source with constant pressure function according to claim 1, characterized in that: The pump source eliminates the external mechanical connection of the LS feedback oil circuit and P port feedback oil circuit, and transmits differential pressure information through electronic signals, eliminating the need for damping orifices or blind pipes in the oil circuit to suppress vibration.

7. The control method for an electrically controlled load-sensitive pump source with constant pressure function according to any one of claims 1 to 6, characterized in that: Includes the following steps: a. The system performs a power-on self-test. The target working mode is selected and the corresponding target parameters are input through the host computer (5). b. If the constant pressure control mode is selected, the differential pressure calculation logic and flow calculation logic of the differential pressure controller (6) are shielded; the differential pressure controller (6) receives the target pressure command sent by the host computer (5) and sends the target pressure command to the pump control controller (4). The pump control controller (4) collects the pressure feedback signal detected by the first pressure sensor (13) in real time, calls the internal pressure PID adjustment module to perform closed-loop calculation, drives the proportional directional valve (3) to act according to the calculation result, adjusts the swashplate angle of the electro-hydraulic proportional variable pump (1) to change the pump output displacement, dynamically compensates the system pressure fluctuation, and finally maintains the constant pump source outlet pressure. c. If the constant pressure proportional flow control mode is selected, the differential pressure calculation logic of the differential pressure controller (6) is shielded; while the differential pressure controller (6) sends the target pressure command to maintain the constant pump source outlet pressure, it controls the output flow by adjusting the opening of the proportional speed control valve (10) according to the real-time flow feedback from the flow meter (9). d. If the proportional flow control mode is selected, the differential pressure calculation logic of the differential pressure controller (6) is shielded; the maximum pressure limit signal and the target displacement signal are input to the pump control controller (4), and the full-open control signal is input to the proportional speed control valve (10) at the same time, so that the valve port of the proportional speed control valve (10) is kept at the maximum opening; the pump control controller (4) drives the proportional reversing valve (3) to adjust the pump swashplate tilt angle according to the target displacement signal and the feedback of the swashplate tilt sensor (2), thereby directly controlling the pump source output flow and realizing pump control proportional flow regulation; e. If the load-sensitive control mode is selected, the flow calculation logic of the differential pressure controller (6) is shielded; the differential pressure controller (6) calculates the real-time pressure difference ΔP=P1-P2 at both ends of the valve under test, compares ΔP with the target pressure difference ΔPref, and outputs the discharge adjustment signal to the pump control controller (4) so ​​that the pressure difference at both ends of the valve under test tracks the target pressure difference ΔPref.

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