Analysis of common faults in the maintenance of single-plunger hydraulic pumps

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Analysis of common faults in the maintenance of single-plunger hydraulic pumps: The common faults in such hydraulic systems can be categorized into four types: inability to lift under no-load conditions； Heavy load cannot be lifted ； The speed of improvement is slow, accompanied by shaking ； After the upgrade, the implement descends more quickly when the control lever is in the neutral position. When performing fault analysis on hydraulic systems, it can be divided into two sections: the tank and the oil pump constitute the first section, which is responsible for supplying oil and converting low-pressure oil into high-pressure oil; it serves as the power source of the hydraulic system ； Designate the cylinder as the second section. 1. With no load, loosen the connection fitting between the oil pump and the cylinder, and observe the operation of the oil pump. If oil is pumped, it indicates that the first section is working properly ； Conversely, it indicates a fault in the first section. 1. It belongs to the first section fault (1): the separation block is stuck. Place the clutch lever in the engaged position and observe how far the top of the release shaft drops; if it does not drop sufficiently, it indicates that the release plate is stuck. At this point, the three bolts that hold the oil pump in place can be slightly loosened, and the position of the oil pump can be adjusted slightly to eliminate the jamming of the separation block; afterwards, the three bolts should be tightened evenly. (2) There is too little hydraulic oil; the tank is low on oil. It can be observed through the transparent plastic tube of the low-pressure oil line, or by loosening the connection of the low-pressure oil tube. If the oil level is too low, add hydraulic oil. (3) Severe oil leakage in a certain area, such as an uneven sealing surface of the check valve or the presence of debris there ； Damage to the sealing ring band of the safety valve’s ball, or its getting stuck due to debris, can all prevent the oil pump from pumping oil. Restore its sealing performance by cleaning the dirt or grinding it. (4) The first shaft of the gearbox cannot rotate properly. For example, if the clutch slips severely and the clutch pedal is in the disengaged position, the oil pump loses its power and therefore cannot rotate. (5) A large amount of air enters the low-pressure oil circuit; the air bubbles prevent the hydraulic oil from flowing, and this can be seen directly. Loosen the check valve nut to release the air. (6) The bearing ring of 108 broke, the steel balls fell out, and the debris resulting from this breakage got stuck in the gear mechanism; the driver did not hear any noise indicating damage, and as a result the plunger stopped pumping oil. At this point, the oil pump should be removed for inspection; if bearing 108 is damaged, the gear oil should be drained, all debris removed thoroughly, and then bearing 108 should be replaced. (7) The plunger is stuck inside the pump body; turn the clutch handle by hand to determine whether the plunger is stuck based on feel. If the separation is easy, it indicates that the plunger spring is in a compressed state and the plunger has become stuck inside the pump body. There are three reasons for the plunger getting stuck: ① The oil pump has been operating for a long time under heavy load, or it has been running without oil for an extended period, or the clearance between the components is too small, leading to poor lubrication and high temperatures, all of which can cause the plunger to get stuck. If the strain is severe, a new pump should be replaced ； If the strain is mild, sand the affected area with fine sandpaper to smooth it out, after which it can be used again. ②The newly installed oil pump is prone to plunger jamming, which is mainly caused by inconsistent tightening torques of the three bolts securing the pump; these bolts can be tightened slightly. Slightly move the position of the oil pump, then tighten the three bolts evenly. ③The hydraulic oil contains many impurities, which cause damage to the mating surface between the plunger and the pump body, leading to jamming. 2. It belongs to the fault of the second section: (1) The connecting pin between the rod and the inner lifting arm breaks, causing the rod to detach and the inner lifting arm to lose power. The diagnostic method is as follows: while the hydraulic pump is operating normally, manually lift the outer lifting arm several times to feel whether the inner lifting arm pushes the piston; if no force is felt, it can be generally concluded that the inner lifting arm has become disconnected from the linkage. At this point, the rear cover should be removed for inspection. If the connecting pin between the inner lift arm and the linkage is broken, a slightly thinner pin can be used so that the pin does not bear the force directly; instead, the spherical surface of the linkage comes into direct contact with the concave surface of the inner lift arm to transmit power. Otherwise, the pin will continue to break. When the pin connecting the rod to the inner lifting arm breaks, the spherical end of the rod may come into direct contact with the edge of the recess in the inner lifting arm, which effectively lengthens the rod. During lifting, the piston fails to reach the oil release position on time; as a result, the connecting rod may break the inner lifting arm, or even puncture the rear cover. This type of failure is accompanied by a certain noise; once it is detected, the machine should be stopped immediately and new parts replaced. (2) The cylinder and piston are stuck together; the hydraulic oil is too dirty, causing damage to the piston and the cylinder walls ； Or the clearance between the piston and the cylinder liner is too small; after prolonged operation at high temperatures, the piston gets stuck in the cylinder liner. The diagnostic method is as follows: when the oil pump is operating normally, loosen the oil pipe connection between the oil pump and the cylinder; high-pressure oil will be emitted, but the outer lifting arm will not move upward. The exclusion method is: disassemble the cylinder. If the cylinder and piston are severely damaged, they should be replaced with new parts ； If the strain is mild, you can polish the affected area with fine sandpaper and then reinstall it for use. II. Failure to lift under heavy load 1. It belongs to a fault in the first section: (1) The setting pressure of the safety valve is too low; adjust the pressure of the safety valve. (2) The mating surface between the plunger and the pump body is severely worn; this phenomenon is mainly due to the long service time of the hydraulic system. Generally, when the cumulative working time reaches 1500 hours or more, as measured with a small internal diameter dial indicator, the clearance between the components must not exceed 0.03 mm. If this clearance is too large, it will affect the plunger’s ability to pump oil, leading to oil leakage or air ingestion. (3) Air mixed in the hydraulic oil should be removed. (4) The sealing surface of the safety valve ball is contaminated with dirt, or its sealing performance is poor, especially in the case of check valves. If there is dirt between the lower surface of the check valve body and the sealing surface in contact with the pump body, it should be removed. The sealing surface of the valve body should be polished on a flat fine-grit sandpaper to restore its sealing properties. 2. It belongs to the fault in the second section: (1) The sealing steel ball of the oil leakage hole at the top of the piston loses its sealing function, resulting in severe oil leakage. This type of fault is difficult to detect from the outside; it is necessary to disassemble the cylinder in order to carry out an inspection. (2) Severe wear of the piston and cylinder, as well as damage or severe strain on the sealing rings, leads to oil leakage and affects the lifting force. (3) The oil inlet pipe at the top of the cylinder is loose, resulting in severe oil leakage. If the screw holes on the cylinder are damaged, a new cylinder should be replaced.