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The excavator hydraulic cylinder is difficult to check because of its complex structure and bad working condition.

Oil Spill

The external surface area of the hydraulic cylinder can see the leakage of oil, resulting in the reduction of system pressure. Hydraulic cylinder oil leakage is divided into dynamic sealing oil leakage and static seal oil leakage. Dynamic seal oil leakage mainly reflects in the direction of the guide sleeve along the rod oil leakage. The leakage of static seal mainly reflects the oil leakage of the joint surface of the guide sleeve and the cylinder.

Lock seat joint surface oil leakage. The main failure phenomenon of oil leakage are piston rod oil, guide sets of static seal leakage, valve seat joint surface leakage, oil pipe crack leakage. Seal failure causes oil in piston rod between piston rod and guide sleeve or by surface failure of rod body. The common failure modes are: dynamic seal failure, piston rod surface strain, electric shock injury on the surface of piston rod, coating cracks on piston rod and so on.
Solution: direct replacement of the corresponding seal due to seal failure, due to piston rod surface failure. According to the actual damage area and depth to determine the site repair or replacement of new piston rod or the whole cylinder.

Guide sleeve static seal leakage, mainly refers to cylinder cylinder and guide the static seal failure. Failure modes are: seal ring quality is not good; Insufficient compression of seal ring. The seal ring is scratched or damaged. The surface of the guide sleeve sealing groove is rough.
Solution: If the static seal fails, directly replace the static sealing. The surface of the sealing groove of the guide sleeve is rough and needs a new guide sleeve.

Valve seat joint surface leakage, mainly due to rough valve seat surface. O-ring wear or vibration caused by the lock bolt loosening.
Solution: Replace damaged O-rings or tighten bolts.

The main cause of oil leakage is the oil pipe cracking caused by the problem of oil pipe material.

Solution: Replace the new tubing.

Internal leakage

The internal leakage of hydraulic cylinder refers to the leakage of oil from the high pressure area to the low pressure area inside the hydraulic cylinder. Which reduces the output force of the cylinder and causes the hydraulic hydraulic cylinder to not work normally. Internal leakage of the main fault phenomenon are: off arm or lock, hydraulic cylinder expansion slow, gas explosion and so on. Excavator hydraulic cylinder leakage can measure and evaluate by settlement. The operation of the excavator to make the hydraulic cylinder extended at the highest point. To place a certain time, measuring the height of the drop, more than allowed to appear within the leakage. The failure modes of hydraulic cylinder leakage include: piston seal failure, piston strain, cylinder bore strain, nut loosening / falling off, etc. The main cause of the strain is oil solid particle pollution.
Solution: Piston seal failure requires replacement of piston seal. Repair of strains on the piston surface. Cylinder surface failure according to the actual damage area and depth to determine the site repair. Replace the new piston rod or the whole cylinder, if the serious strain need to replace the hydraulic oil. Nut loosening / shedding requires a certain tightening torque and loosening screws for reinforcement.

The main reason is that the hydraulic cylinder enters the air or the air of the new car is not completely discharge. The host suddenly moves quickly, and the internal temperature of the cylinder rises sharply to produce the gas explosion and seal damage, resulting in the leakage of the hydraulic tank.
Solution: The new car or replacement of the new cylinder should first repeatedly slow motion exhaust the air in the hydraulic cylinder. Improve the host hydraulic system in the supplementary valve performance. Or in the piston burning wall additional metal system or metal such as bronze, cast iron and other added sealing ring or anti-fouling ring.

For internal leakage, prevention methods are:

  1. Use the hydraulic oil brand recommended by the host company to avoid the mixing of different grades of hydraulic oil;
  2. After the excavator is stationary for a period of time, to avoid the rapid action after starting. It should be repeated in slow motion several full stroke to discharge the air in the hydraulic cylinder;
  3. Hydraulic cylinder maintenance requires professional maintenance personnel to avoid dust and impurities entering the hydraulic cylinder during maintenance.

Weld Leakage

Weld leakage, refers to the hydraulic cylinder weld position of the oil leakage to the outside phenomenon. Common are: cylinder and cylinder bottom weld leakage, cylinder and flange weld oil leakage, oil pipe weld leakage. The main cause of oil leakage in the weld seam between the cylinder body and the cylinder bottom is the defects. Such as weld holes and sand holes in the cylinder during processing.
Solution: replace the new cylinder or cylinder, do not recommend repair welding maintenance continue to use.

The main reason for oil leakage in the weld between cylinder and flange is the excessive buffer pressure or the defects of weld porosity and sand holes in the cylinder during machining.
Solution: replace the new cylinder or cylinder, do not recommend repair welding maintenance continue to use.

Oil leakage of tubing weld is the phenomenon of oil leakage between the tubing assembly and the joint or the tubing flange. The main reason is the defects such as weld blowholes and sand holes in the tubing assembly during processing.
Solution: professional repair point repair welding or replacement of new parts.

Appearance Defects

Appearance defects refer to irreversible defects in the appearance of hydraulic cylinders that affect the appearance or performance of the product. It mainly include: piston rod rust or coating off, piston rod black and hydraulic cylinder non-matching surface bump problems. Piston rod corrosion or coating shedding, the main reason is that the piston rod coating in the processing process of the process parameters are unreasonable or the use environment exceeds the design permit (such as offshore environment or strong corrosion environment).
Solution: replace the piston rod / cylinder, adjust the process parameters. The use of environmental problems requires the selection of coatings with stronger corrosion resistance according to the actual working conditions.

The piston rod is black, mainly due to poor heat dissipation of the host, replacement of inferior hydraulic oil or replacement of poor seals.


  1. Regularly clean the radiator part, and check the tank cooling system, whether there is blockage, out of control, etc., to ensure the heat dissipation effect;
  2. It is recommended to select the imported seal or the domestic big brand seal brand and material suitable for the host condition;
  3. Adopt the hydraulic oil brand and grade specified at the time of purchase of the host. The black phenomenon of the rod body found in the market is generally caused by the high temperature of the hydraulic oil and the mixing of the fluid.

The main reason for the non-matching surface bump of hydraulic cylinder is that the hard objects such as stones collide with non-matching surfaces during the working process.
Solution: Under the premise of not affecting the use of surface grinding, painting.

Failure of Weight

Weight-off failure refers to the failure of the structure of the hydraulic cylinder, such as abnormal or damaged, which makes the cylinder unable to work, resulting in heavy-off parts or even the whole hydraulic cylinder scrapped. Other common faults are: cylinder bending, cylinder drum drum / burst, piston rod bending, the bottom of the cylinder casting forging crack / fracture, earring rod weld crack / break, bushing abnormal wear, buffer effect abnormal or no buffer, etc. Cylinder bend, cylinder drum belly / burst, piston rod bend, mainly due to illegal operation or overload work.
Solution: replace the cylinder, piston rod or the entire cylinder.

The main reason is illegal operation or overload work.
Solution: replace the cylinder, piston rod or the entire cylinder.

The abnormal wear of the bushing is mainly caused by insufficient lubrication or the entry of solid particles.
Solution: regularly lubricate and check whether the shaft on both sides of the bushing is in good condition.

The buffering effect is abnormal or no buffering, the main reason is that poor cleanliness leads to abnormal wear or strain of the buffer sleeve / buffer plunger mating surface, resulting in poor or no buffer effect.
Solution: replace the hydraulic oil in time, replace the buffer sleeve / buffer plunger or replace the whole cylinder.


Other failures refer to all failures except oil leakage, internal leakage, external defects and failure of heavy parts. Other common faults are: hydraulic cylinder creep / jitter, hydraulic cylinder rebound / sound, tubing deformation, etc. Hydraulic cylinder creep / jitter refers to the phenomenon of hydraulic cylinder crawling / jittering at low speed, mainly due to the hydraulic cylinder entering the air.
Solution: Add low-friction lubricating oil or run a few cycles after the system is started. Empty the air in the hydraulic cylinder, and then work with the load.

Hydraulic cylinder rebound / sound, mainly due to hydraulic cylinder into the air.
Solution: After the system is started, it is necessary to run several cycles. Empty the air in the hydraulic cylinder. And then work with the load.

The main reason of tubing deformation is that tubing is collided with foreign bodies during operation.
Solution: affect the use of performance in the regular repair shop to restore the shape or replace the tubing assembly.

Tongzhou Excavator Boom Cylinder Assy