Is the servo valve important in the variable system?
It can be said that its function is very important, because its working frequency is relatively high, so many faults appear in this part. When the input signal pressure is Pi, from the D hole acting on the C chamber of the control piston, the pressure Pc of the control pump is transferred to the B hole. If Pi rises slightly, the oil pressure acting on the C cavity also rises slightly. Therefore, the piston is pushed to the spring and shifted to the left, and the lever arm is supported by the servo valve piston and swinging to the left, so that the pilot valve moves to the left. Because of the movement of the guide valve, the B hole is connected with the a hole. The pressure of the control pump is transferred to the B cavity of the piston of the servo valve, and the servo piston moves to the left, making the plunger pump's tilt angle larger and the flow increase.
When the arm rod is clockwise, it rotates clockwise to move the guide valve to the right, blocking the B hole and the a hole, and the C hole and the discharge circuit, which is equal to the input signal pressure R of the oil discharge.
Here is a brief description of the servo piston moving to the right when the servo piston is in balance in a certain position. When the pressure Pi drops, the piston moves to the C cavity, the pole arm moves to the right with the servo piston to the right, and the guide slide valve moves to the right. The loop between the B hole and the a hole is cut off because of the movement of the guide valve. And the C hole is connected to the discharge circuit. In addition, the B hole is connected with the C hole, the oil flow enters the A chamber of the servo cylinder, and the servo piston is pushed to the right side, so that the inclination angle of the plunger pump decreases, and the pump flow becomes smaller. At this point, the rod arm is centered on the pin and rotates in the counter clockwise direction, so the guide slide valve moves to the left, the B hole and the C hole, and the a hole and the discharge hole are cut off. In this way, the amount of oil discharged from the input signal is reduced.
How should the 2. servo valve adjust the screw?
The adjusting screws of the servo valves have been adjusted at the time of leaving the factory, and users are not allowed to adjust them at will. For those machines that use longer time, they should be adjusted to the front and rear pumps respectively. First, track the weak track side up, then the corresponding front pump or rear pump servo valve. To maintain the top of the track is constantly rotating, so as to observe the effect of adjustment. First adjust the screw to half circle. If the original adjustment is improper, when the screw is screwed out half circle, the track speed will change. Then turn the inner adjusting screw out of the half circle, or you can turn the two adjusting screws inside and outside more.
If the two internal and external adjusting screws are adjusted, the track is still very slow. This is the servo stem arm broken off or latch out.
3. after adjusting the servo valve, the track on both sides has been speeded up, but it still has not met the requirement. What is the reason?
The aperture of the servo valve A cavity and the B cavity is larger due to the larger wear and the large gap between the servo piston and the servo piston.
The worn holes usually have obvious steps and roundness. When repairing, Kong Tangyuan is first repaired and then grind, and the piston is then fitted according to the size of the repaired aperture. The aperture has been repaired. The piston is repaired according to the size of the hole, and the clearance between the hole and the piston is about 0.10mm. The surface of the piston is treated by heat treatment.
4. if the size of the piston has been changed after repair, will it affect the propelling force of the piston?
Meeting
5. is not enough pressure to control the pump has been damaged?
It can not be concluded that there is a pressure regulating valve in the control pump. If the adjustment valve is defective, the pump pressure can not be improved. It is only necessary to check the pressure relief valve carefully before drawing a conclusion. The pressure regulating valve of Komatsu excavator is the same. The pressure regulating valve is a pilot type pressure regulating valve. There is a damping hole in the middle of the piston. When checking, check carefully whether there is any blockage in the damping hole. It is the main cause of pressure improvement. There are spring, cone valve and cone valve on the integrity of the spring 2, all of the pressure regulating valve has an impact. The check valve can be installed and debugged after the check valve is completed. If the pump pressure is still not up to the specified value, it can be judged that the pump is damaged.
6. when the control pump pressure reaches the specified value, what is the reason why the whole machine is still weak?
The above steps can be checked according to the following steps. 2 58.8MPa oil pressure gauges are installed on the pressure gauges on the outlet of 2 main oil pumps respectively. Then increase the throttle, let the piston rod of the dug cylinder stretch out, so that the overload relief valve is in the overflow condition. At this time, the value of the 1 oil pressure gauges should be higher, to observe whether it can reach the specified value. The PC200 excavator is 26MPa, the PC300 excavator and the PC400 2 excavator are 26MPa, PC400 - 3, PC400 - 5 and PC400 - 6 are 32MPa, in the same way, and then another pressure gauge pressure. If the pressure is insufficient, it is still not effective after adjusting the 2 pressure regulating valves. Remove the main pressure regulating valve (also called the main safety valve) to check, check the method and check the pressure control valve of the pump. If there is no fault in the pressure regulating valve, third steps of inspection will be carried out. That is, check the oil pump has no internal leakage.
7. when measuring pressure, it can reach the specified value at the beginning, but it will drop to 20MPa soon. Is this normal?
Abnormal. Generally speaking, as long as the overload overflow valve is still overflowing, the pointer reading should not be lowered.
8. how to check the internal leakage?
The machines with internal leakage are generally old machines. The wear of parts is serious, the clearance is large, and they are synchronous wear. In the daily work of machines, we can find that machines with internal leaks are more noisy and faster. Internal leakage can be checked by the following measures. Put out the hydraulic oil in the oil pump, dismantle two high-pressure oil tubing, and then use diesel oil into the pipe mouth, if the oil surface drops very quickly, the oil pump has internal leakage; if it is PC200 1 and PC200 - 2 type, in addition to the internal leakage of the oil pump, the oil pump oil outlet and the tubing connection part of the seal will also leak.
9. plunger piston plunger wear will produce internal leakage?
Theoretically, the clearance between plunger and column plug should not be greater than 0.05mm. Because the aperture is small, it is difficult to measure, usually can be tested by the following method, that is, the hole of the plunger head is sealed with the finger, the plunger hole is sealed with the hand at the same time, and then the plunger is pulled back. If the plunger is not pulled and has strong suction, it means that the fit clearance is good, otherwise new parts should be replaced.
How do 10. slipper work in a skew plate?
The ball head of the plunger is in contact with the inner surface of the slipper, and can rotate in any direction, while the slipper plane is in contact with the swashplate. In addition, through the small hole F of the plunger and the pinhole G on the slipper, the pressure oil is introduced into the A cavity, so that the slipper and the skew pan form an oil film, that is, the hydrostatic bearing is formed. When the pump works, the pressure oil P acts on the plunger and produces a normal compression force N for the slipper to press the slipper toward the surface of the inclined disk, and the oil pressure P 'of the oil cavity A and the liquid pressure between the slipper and the slanted disc give a reverse thrust F to the slipper, and the slipper is in the balance condition when the reverse thrust F is equal to the tightening force N.
The balance process of the slipper is so. When the pump starts to work, the slipper is clinging to the inclined plate, because the oil in the oil chamber A is not flowing, so it is in a relatively static state. At this time, P '= P, in which the reverse thrust F is greater than the compression force N, so that the slipper is gradually pushed open, the gap is h, and the oil in the A cavity is leaked through the clearance. The oil film is formed and the oil in the A cavity is in the flow state, so the pressure oil P is damped through the hole F and G to the A cavity. Due to the resistance loss of the damping hole F and G, the P 'is less than P, until the reverse thrust F and the compression force N are equal, so that the slipper slanting disk keeps a certain oil film thickness and is in the new equilibrium state.
