1. Plunger cylinder
1. Insufficient thrust
① The pressure of the hydraulic system is insufficient. Check the relief valve and increase the system pressure.
②After the plunger and guide bush are worn, the gap increases and the oil leakage is serious. 03mm。 Replace the guide sleeve, the inner hole and the outer circle of the plunger fit clearance is 0. 02-0. 03mm.
③The oil inlet pipe joint is damaged or the nut is not tightened, and the oil leaks seriously. Replace pipe joints or tighten nuts to prevent oil leakage.
2. Crawl while working
① The axial line of the plunger cylinder is eccentrically compressed. The parallelism should be within 0.1 ~ 0.2mm.
②The axis line of the plunger cylinder is not perpendicular to the acting end. The verticality should be about 0.1mm.
③ The clearance between plunger and guide bush is too small. It is required to be in the range of 0.02 ~ 0.03mm.
Second, Kobelco excavator piston cylinder
1. Creeping or local uneven speed
① Gas is mixed in the cylinder. Open the exhaust valve to quickly exhaust the cylinder. An exhaust valve is added without an exhaust valve.
② There is an error in the coaxiality between the piston rod and the piston.
③The piston rod is partially bent. Correction, the correction value of the total length of the rod should be within 0.2mm.
④The sealing ring is pressed too tight or too loose.
⑤ Low installation accuracy. The parallelism and perpendicularity should be within the range of use.
⑥ Corrosion or brushing in the cylinder. When slight, repair rust spots and burrs. In severe cases, it is processed through a lithium bed.
⑦The rod end nut is tightened too tightly, which deforms the piston rod. The rod end nut should not be tightened too tightly. Generally, tighten it slightly (the small cylinder can be tightened by hand) to keep the piston rod in a natural state, and then use two wrenches to lock the double nut.
2. The piston rod or cylinder cannot move
① No long-term corrosion. Remove and wash, repair rust spots, when serious, re-grind iron, and then match the piston.
②. The sealing ring is aging, failure, and serious internal leakage. replace.
③The precision in the cylinder is poor, and the surface is rough or damaged, which increases the internal leakage. Repair or replace.
④ Dirt enters the lubricated parts. Remove and wash, replace oil if necessary.
⑤Cylinder end seal is damaged. replace.
⑥ The assembly quality of the cylinder is poor (the coaxiality error between the rod, the piston and the end face is large, the installation accuracy is low, etc.). Re-assemble and install, and substandard parts should be replaced.
3. Insufficient thrust, slow working speed.
①The clearance between the red hole and the piston is too small or the groove is too shallow, which makes the O-ring seal form too much resistance. Rearrange the gap and deep groove.
②The gap between the cylinder and the piston is too large, so that the high and low pressures on both sides of the piston can communicate with each other. Reassemble the piston.
③The piston rod is bent. Corrected, the total length is within 0.2mm.
④The sealing ring in the end face is pressed too tightly. Appropriately loosen the compression screw to the limit of no leakage.
⑤ System leakage, resulting in insufficient pressure and flow. Identify leaking parts of the system, tighten the joints or carry out the relevant sealing treatment. When the flow is insufficient, it is more necessary to check whether the output flow and pressure of the pump reach the rated value.
⑥ The cylinder tubing was squashed due to poor assembly. Replace the tubing and avoid squashing again.
⑦ System pressure adjustment is low. Adjust the pressure of the relief valve system within the specified range.
⑧ The oil temperature is too high. When the oil temperature exceeds the specified value, the system should be cooled before working.
4. Serious leakage
External leakage is one of the most problematic problems in the piston cylinder, and it is also the most affecting safety and environment.
(1) Piston rod leakage
① Leakage caused by seal wear. The cause of seal wear is usually caused by particles in the bush after sliding wear. For leaks caused by damage to seals, the most critical thing for Y-shaped seals is the lip. When installing the seal, the lips must never be damaged. The seal should be free of burrs and the transition should be smooth. The sealing lip cannot be installed incorrectly or improperly, not to mention reversely. For the small Y shape (ie Yx shape), pay attention to both the shaft and the hole. The short lip should have a relative movement side (for the piston, the small Yx short lip is the relative movement side with the cylinder) , Don't get it wrong. Sometimes, although the seal ring is not damaged, the seal lip is relatively rough, which can also cause leakage.
② Leakage caused by permanent deformation of the sealing rubber after compression. Due to the material of the seals, the rubber loses its elasticity due to long-term compression use, resulting in leakage.
③ Leakage caused by foreign impurities entering the seal. The sealing lip sometimes causes damage and leakage due to the mixing of small external sand particles from the movable end of the cylinder rod. For this reason, sealed dust covers should be used for protection in the field.
④The seal ring for the cylinder was incorrectly used. For the V-shaped seal, the lip end of the V-shaped seal ring for the cylinder is sharp-angled, which makes the piston rod scrape the oil during the reciprocating movement, thereby causing the oil droplet to fall. The lip end of the V-shaped seal ring used in the hydraulic cylinder is rounded, which forms a thin oil film on the piston rod for lubrication.
(2) External leakage caused by the joint between the cylinder and the end cover
Cylinder barrel and end cover are combined with bolt fastening and threaded connection.
① Bolt tightening method. Bolt fastening methods include flange connection, half ring connection and fixed bolt connection. In this way, there are two kinds of O-ring seal and end seal. In the O-ring sealing method, leakage occurs from the fit gap; in the end face sealing method, if the bolt is not properly tightened, leakage will also occur.
②Thread connection method. There are two types of thread connection: internal thread and external thread. In the case of large diameters, because the force of tightening the end caps often fails to reach the rated torque and may increase leakage, a special tool must be used to tighten and reach the required torque value.
(3) Leakage caused by hydraulic cylinder inlet
This is mainly caused by the looseness of the nozzle caused by the impact of the oil inlet pressure or the vibration during work, which requires frequent inspection and tightening.
