Because of the large number of cylinders used in the hydraulic system of the forming machine and the different loads in the various stations, it makes sense to use a variable displacement pump in the system. Qinghai Branch of the hydraulic system used in the molding machine are KHD's constant pressure variable displacement pump. The maximum output pressure of the pump 40MPa, and has low noise, long life, axial radial load, low power consumption, manifold design and control of rapid, from start to finish with a pump locator and so on. First, the working principle With a sliding shoe structure of the axial piston pump is currently the most widely used axial piston pump, placed in the cylinder plunger through the sliding shoe contact with the swash plate, when the drive shaft to drive the cylinder rotation , The swash plate will pull the plunger out of the cylinder or push back to complete the suction and discharge process. The oil in the working chamber composed of the plunger and the cylinder bore respectively communicates with the suction and discharge chambers of the pump through the oil distribution plate. The variable mechanism is used to change the inclination of the swash plate. The displacement of the pump can be changed by adjusting the inclination of the swash plate. Second, the maintenance of piston pump Swash plate axial piston pump generally adopts cylinder rotation, face with the flow of the form. The cylinder end is inlaid with a friction pair composed of bimetal plate and steel with oil pan, and most of them adopt the method of plane distribution, so maintenance is more convenient. With the oil pan is one of the key components of the axial piston pump, the pump work, on the one hand the working chamber of the high-pressure oil to push the cylinder with the oil pan, on the other hand with the oil pan and the formation of oil film pressure between the cylinder Cylinder hydraulic reverse thrust cylinder away from the oil pan. The design pressure of the cylinder to the oil pan is slightly larger than the hydraulic thrust Ff of the oil pan to the cylinder, that is, Fn / Ff = 1.05-1.1, which makes the pump work normally and maintains a high volumetric efficiency. In fact, there is often slight wear between the oil pan and the cylinder due to oil contamination. Especially when the high pressure, even slight wear can make the hydraulic thrust Ff increases, thus undermining the Fn Third, the common troubleshooting 1. Hydraulic pump output flow is not enough or not output fluid (1) Insufficient suction. The reason is that the resistance of the oil suction pipe is too large or the amount of oil is insufficient. Such as the pump speed is too large, the tank surface is too low, into the tube leakage, filter plug and so on. (2) the amount of leakage is too large. The reason is the pump gap is too large, caused by poor sealing. Such as oil pan with metal fragments, iron filings and other scratches, face oil spills; variable mechanism in the check valve sealing surface with poor pump and oil pan bearing surface with trachoma or scratch and so on. Can check the pump body of hydraulic oil in the foreign material to identify the pump is damaged parts. (3) The tilt angle of the swash plate is too small, and the displacement of the pump is small. This requires adjusting the variable piston and increasing the inclination of the swash plate. 2. When the median displacement is not zero variable axial piston pump swashplate inclination of zero called the median, then the pump output flow should be zero. However, there is a tendency that the center deviates from the midpoint of the adjustment mechanism and there is still flow output at the midpoint. The reason for this is that the controller is out of position, loose or damaged, requiring zeroing, fastening or replacement. Insufficient pump force to maintain the angle of the trunnion wear will have this phenomenon. 3. Output Flow Fluctuation The output flow fluctuations depend on many factors. The variable pump can be regarded as the poor control of the variable mechanism, such as foreign body into the variable body, the control piston on the draw marks, wear marks, scars, etc., resulting in control piston instability. Due to insufficient energy in the amplifier or damaged parts, the damping effect of the spring-containing control piston is poor, resulting in unstable control piston motion. Flow instability is often accompanied by pressure fluctuations. Such failures generally open the hydraulic pump, replace damaged parts, increase damping, improve the spring stiffness and control pressure. 4. Output Pressure Abnormal The pump output pressure is determined by the load and is approximately proportional to the input torque. There are two types of output pressure abnormalities. (1) the output pressure is too low When the pump in the self-priming state, if the leakage of oil into the pipeline or hydraulic cylinder in the system, one-way valve, valve and so have a larger leak, will make the pressure rise. This requires finding leaks, tightening, and changing seals to increase pressure. Pressure relief valve or adjust the pressure is low, the system pressure also does not increase, the pressure should be re-adjusted or overhaul relief valve. If there is a large amount of leakage due to the deviation between the cylinder of the hydraulic pump and the valve plate, in severe cases, the cylinder may rupture. Then, grind the mating surface or replace the hydraulic pump. (2) the output pressure is too high If the loop load continues to rise, the pump pressure continues to rise, it is normal. If the load is constant and the pump pressure exceeds the pressure required by the load, check the hydraulic components other than the pump, such as the directional valve, pressure valve, transmission, and return line. If the maximum pressure is too high, should adjust the relief valve. 5. Vibration and noise Vibration and noise occur simultaneously. They not only endanger the machine operator but also pollute the environment. (1) Mechanical vibration and noise If the shaft of the pump and the motor shaft are not concentric or dead, the shaft bearing, coupling damage, pad damage and loose assembly bolts will produce noise. For high-speed operation or transmission of large energy pump, to regularly check and record the amplitude of each component, frequency and noise. If the frequency of rotation of the pump is the same as the natural frequency of the pressure valve, it will cause resonance and change the speed of the pump to eliminate the resonance. (2) the noise generated by the pipeline flow into the oil pipeline is too small, into the oil filter through the flow capacity is too small or blocked, the intake pipe into the air, the oil is too high, too low oil surface oil shortage and high pressure pipe In the liquid hammer and so on, will produce noise. Therefore, the correct design of the fuel tank, the correct choice of oil filters, tubing and directional valve. 6. Hydraulic pump overheating Hydraulic pump overheating for two reasons, one is mechanical friction heat. Due to the dry or semi-dry friction surface, the moving parts friction and heat. Second, liquid friction heat. High-pressure oil leaks into the low pressure chamber through various gaps, and a great deal of hydraulic pressure can be lost to heat energy. Therefore, the correct choice of moving parts between the gap, the tank volume and cooler, can prevent excessive pump heat and oil temperature is too high. In addition, back to the oil filter blockage caused by back pressure too high, will cause the oil temperature is too high and the pump overheating. 7. Oil spill piston pump oil leakage mainly for the following reasons: (1) the spindle oil seal damage or shaft defects, scratches; (2) the internal leakage is too large, resulting in increased pressure at the seal, and seal damage or out; ( 3) the drain pipe is too thin, so that the seal leaks; (4) pump external tubing loose, pipe joints damage, gasket aging or cracks; (5) variable adjustment mechanism bolts loose, seal damage; Pump casing with trachoma or poor welding. Now a lot of manufacturers producing piston pumps, imported parts and domestic pieces of different structures, each pump should be strictly in accordance with the instructions of its use of the factory. In the maintenance of the pump, the first pump should be checked in the system installation, the use of proper, easy to find out the causes of damage in time to eliminate hidden dangers and ensure the normal work of the system. Repaired hydraulic pump should pass certain testing equipment testing before use. If you do not have the test conditions, should also be repeatedly debugged in the system so that it can work normally.