The plunger valve is composed of valve body, valve cover, valve stem, plunger, orifice frame, sealing ring, handwheel and other parts. When the handwheel rotates, the stem drives the plunger to reciprocate up and down in the middle of the orifice to complete the opening and closing function of the valve. In the valve between the plunger and the sealing ring using interference fit, by adjusting the flange bolt in the gland to make the lateral force generated by the compression of the sealing ring seal with the hole surface of the valve body and the outer circle of the plunger, so as to ensure the tightness of the valve, eliminate internal and external leakage, and the valve opening torque is small, which can realize the rapid opening and closing of the valve. Compared with globe valves, plunger valves have a long life and low effort to operate. However, the adjustment stroke is longer than that of the globe valve, so throttling control is more difficult than that of the globe valve. Places with clear requirements for regulation, neither is suitable. 　　 　　

      Working principle The interference fit between the plunger and the sealing ring in the valve is adopted, and the lateral force generated by the compression of the sealing ring is sealed with the hole surface of the valve body and the outer circle of the plunger by adjusting the flange bolt in the gland to ensure the tightness of the valve and eliminate internal and external leakage. 　　 　　

     Troubleshooting 1. The output flow of the plunger valve is insufficient or does not output oil

(1) The suction amount is insufficient. The reason is that the resistance on the suction line is too large or the amount of oil replenishment is insufficient. For example, the speed of the valve is too large, the liquid level in the oil tank is too low, the oil inlet pipe is leaking, and the oil filter is blocked. 　　 　　

(2) The amount of leakage is too large. The reason is that the clearance of the valve is too large and the seal is poor. If the oil distribution plate is scratched by metal fragments, iron filings, etc., the end face leaks oil; The sealing surface of the check valve in the variable mechanism is not well matched, and the supporting surface of the valve body and oil distribution plate has trachoma or research marks. The damaged part of the valve can be identified by checking the foreign matter mixed in the hydraulic oil in the valve body. 　　 　　

(3) The inclination angle of the tilt disc is too small, and the displacement of the valve is small, which requires adjusting the variable piston and increasing the inclination angle of the swash plate. 　　 　　

2. The oil discharge amount is not zero when the plunger valve is in the middle position When the inclination angle of the swash plate of the variable axial piston valve is zero, it is called the neutral position, and the output flow of the valve should be zero. However, sometimes the median deviates from the midpoint of the adjustment mechanism, and there is still a flow output at the midpoint. The cause is that the position of the controller is offset, loose or damaged, and needs to be re-zeroed, tightened or replaced. This phenomenon can also be caused by insufficient angle maintenance of the valve and wear of the tilt angle trunnion. 　　 　　

3. Plunger valve output flow fluctuation Output flow fluctuation is related to many factors. The variable valve can be considered to be caused by poor control of the variable mechanism, such as foreign objects entering the variable mechanism, cutting step marks, wear marks, scars, etc. on the control piston, resulting in unstable control piston movement. Unstable control piston movement can occur due to insufficient amplifier energy or damaged parts, poor damper efficiency of the control piston containing the spring. Flow is erratic and often accompanied by pressure fluctuations. Such faults generally require dismantling the hydraulic valve, replacing the damaged parts, increasing damping, improving the spring rate and controlling the pressure. 　　 　　4. The output pressure of the plunger valve is abnormal The output pressure of the valve is determined by the load and is approximately proportional to the input torque. There are two faults for abnormal output pressure. 　　 　　

(1) The output pressure of the plunger valve is too low When the valve is in the self-priming state, if the inlet pipeline leaks air or the hydraulic cylinder, check valve, reversing valve, etc. in the system have a large leakage, the pressure will not rise. This requires finding the air leak, tightening and replacing the seals to increase the pressure. If the relief valve is faulty or the adjustment pressure is low, the system pressure cannot go up, and the pressure should be readjusted or the relief valve should be overhauled. If the cylinder block of the hydraulic valve deviates from the distribution plate and causes a large amount of leakage, and in severe cases, the cylinder block may be ruptured, the mating surface should be re-ground or the hydraulic valve should be replaced. 　　 　　

(2) The output pressure of the plunger valve is too high If the circuit load continues to rise, the pressure of the valve also continues to rise, which is normal. If the load is certain and the pressure of the valve exceeds the pressure value required for the load, the hydraulic components other than the valve, such as directional valves, pressure valves, transmission devices and return pipelines, should be checked. If the pressure is too high, the relief valve should be adjusted. 　　 　　

5. Plunger valve vibration and noise Vibration and noise occur at the same time. They not only cause harm to the operator of the machine, but also cause pollution to the environment. 　　 　　

(1) Mechanical vibration and noise of plunger valve If the valve shaft and motor shaft are not centered or dead, the bearing and coupling of the rotating shaft are damaged, the elastic pad is damaged and the assembly bolt is loose. For valves that operate at high speed or transmit large amounts of energy, it is necessary to check regularly and record the amplitude, frequency and noise of each component. If the rotation frequency of the valve is the same as the natural frequency of the pressure valve, it will cause resonance, and the speed of the valve can be changed to eliminate the resonance. 　　 　　

(2) The noise generated by the liquid flow in the plunger valve pipeline The oil inlet pipeline is too fine, the flow capacity of the oil inlet oil filter is too small or blocked, the oil inlet pipe sucks in air, the oil is too high, the oil level is too low, the oil absorption is insufficient, and the liquid shock is generated in the high-pressure pipeline. Therefore, the oil tank must be correctly designed, and the oil filter, oil pipe and directional valve must be selected correctly. 　　 　　

6. Overheating of plunger valve There are two reasons for excessive heating of plunger valves, one is mechanical friction heating. Since the moving surface is in a state of dry friction or semi-dry friction, the moving parts rub against each other to generate heat. The second is liquid friction heat. High-pressure oil leaks into the low-pressure chamber through various gaps, and a large amount of hydraulic energy is lost into heat. Therefore, the correct selection of the gap between the moving parts, the oil tank volume and the cooler can eliminate the phenomenon of excessive heating of the valve and excessive oil temperature. In addition, the oil return filter is blocked and the back pressure of the oil return is too high, which will also cause the oil temperature to be too high and the valve body to overheat. 　　 　　

7. Oil leakage of plunger valve Oil leakage of plunger valve mainly has the following reasons:

(1) the oil seal of the spindle is damaged or the shaft is defective or scratched;

(2) the internal leakage is too large, causing the pressure at the oil seal to increase, and the oil seal is damaged or flushed out;

(3) the oil drain pipe is too thin and long, so that the oil leakage at the seal;

(4) the external oil pipe of the valve is loose, the pipe joint is damaged, and the sealing gasket is aged or cracked;

(5) the bolt of the variable adjustment mechanism is loose and the seal is damaged;

(6) the cast iron valve casing has trachoma or poor welding.