Failure and elimination of pressure control valve

- Oct 14, 2019-

In the hydraulic transmission system, the hydraulic valve that controls the oil pressure is called a pressure control valve, which is called a pressure valve. Common to this type of valve is the principle of balancing the hydraulic and spring forces acting on the spool.


The pressure control valve plays the role of pressure regulation and constant pressure in the system. It works by the principle that the control oil is balanced with the spring phase. The working state is directly affected by the control pressure, and its state is changed. Find out the structure of various types of pressure valves, and it is easy to grasp the working characteristics of valves under different working conditions.


In a specific hydraulic system, depending on the job requirements, the requirements for pressure control are different: some need to limit the maximum pressure of the hydraulic system, such as safety valves; some need to stabilize the pressure value somewhere in the hydraulic system (or Pressure difference, pressure ratio, etc.), such as relief valves, pressure reducing valves and other constant pressure valves; others use hydraulic pressure as a signal to control their actions, such as sequence valves, pressure relays, etc.


Pressure control valve principle

The pressure valve controls the opening and closing of the oil passage on the valve body by the balance between the spring force and the liquid pressure. The maximum pressure of the system is set by the relief valve, and the working pressure of the system is determined by the external load. The working principle of the pressure valve is shown in Fig. 1. After the oil from the hydraulic pump enters the B chamber, since the two sides are equal in area, there is no axial thrust on the valve core. In the position shown in Fig. 1(a), the spring pushes the valve core to block the P port from the T port, the oil does not leak, the system pressure rises, and the pressure in the A cavity also rises, compressing the force of the spring downward. Continue to increase until the thrust of the spring is exceeded, causing the spool to move downward, as shown in Figure 1(b). Since the P port is connected to the T port, the pressure oil is vented back to the fuel tank through the T port, the system pressure drops, and the pressure in the A cavity also decreases. When the oil pressure is lower than the spring force, the valve core moves up, and the P port and the T are cut off. The connection of the mouth, the oil can not leak, the pressure rises again, the valve core keeps moving alternately, the system pressure is balanced in the dynamic, stable at a certain value, which is the working principle of the pressure valve.


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Failure and elimination of pressure control valve

First, the solenoid valve does not work after being energized


1. Check if the power supply wiring is bad → re-wiring and connector connection;


2. Check if the power supply voltage is within the ± working range - → adjust the normal position range;


3. Whether the coil is desoldered and re-welded;


4. Short circuit of coil → replace coil;


5. Is the working pressure difference inappropriate? Adjust the pressure difference → or replace the proportional solenoid valve;


6, the fluid temperature is too high → replace the proportional solenoid valve;


7. There are impurities to make the main valve core and moving iron core of the solenoid valve be stuck → cleaned. If there is seal damage, replace the seal and install the filter;


8, the viscosity of the liquid is too large, the frequency is too high and the life has reached → replace the product.


Second, the solenoid valve can not be closed


1. The seal of the main valve core or the iron core has been damaged → replace the seal;


2. Whether the fluid temperature and viscosity are too high → replace the solenoid valve of the opposite port;


3. There are impurities entering the solenoid valve to produce the valve core or moving iron core → cleaning;


4, the spring life has been or deformed → replacement;


5, the orifice balance hole is blocked → timely cleaning;


6. The working frequency is too high or the life is up to → re-elect the product or update the product.


Third, other circumstances


1. Internal leakage → check if the seal is damaged and the spring is not properly assembled;


2, external leakage → loose connection or seal is broken → tighten the screw or replace the seal;


3. There is noise when energized → the solid parts on the head are loose and tightened. The voltage fluctuation is not within the allowable range and the voltage is adjusted. The iron core suction surface is dirty or uneven, and it is cleaned or replaced in time.