The hydraulic system mainly includes hydraulic pump, hydraulic cylinder and relief valve, etc. If it goes wrong, firstly, we need to understand the operating conditions of the equipment, including: whether the hydraulic system is working normally; whether there are any abnormalities in the hydraulic pump; the time and results of the hydraulic oil testing cleanliness; the cleaning and replacement of the filter element; whether the hydraulic components were adjusted before the failure occurred; whether the sealing components were replaced; what abnormalities have occurred in the hydraulic system before the failure; what failures have occurred in the system before and how to troubleshoot them, etc.

The following are several common phenomena and handling methods:

Hydraulic Pump of Hydraulic System

Failure Phenomenon

• No oil output, insufficient oil delivery, no pressure up.

• Severe noise and pressure fluctuations.

• Hydraulic pump journal oil seal leakage.

Failure Analysis

• The motor is not turning right; the oil suction pipe or filter is blocked; the axial clearance or radial clearance is too large; leakage at the connection, mixed with air; oil viscosity is too large or oil temperature rise is too high.

• The oil suction pipe and filter are blocked or the filter capacity is small; air leakage at the suction pipe seal or bubbles in the oil; hydraulic pump and coupling are not centered; low oil level; low oil temperature or high viscosity; damaged hydraulic pump bearing.

• The liquid resistance of the oil leakage pipeline reaches large, so that the pressure inside the pump rises above the permitted pressure resistance value of the oil seal.

Exclusion Method

• Check motor steering; unclog the pipe, clean the filter and change the new oil; check and replace relevant parts; tighten the screws at each connection to avoid leakage and prevent air from mixing in; correctly select the oil and control the temperature.

• Clean the filter so that the oil suction pipe is smooth, and choose the filter correctly; add some oil to the connection part or seal. If the noise is reduced, tighten the joint or replace the seal.

• Check whether the drainage port on the pump body of the hydraulic piston pump is directly connected to the oil tank with a separate oil pipe. If it is found that the leaky oil pipes of several hydraulic piston pumps is connected to the tank after connecting to a total pipe of the same diameter, or the drainage pipe of the hydraulic piston pump is connected to the total return pipe, it should be corrected.

Hydraulic Cylinder of Hydraulic System

Failure Phenomenon

• Crawl.

• Impact.

• Insufficient thrust or gradual decrease or even stop of working speed.

Failure Analysis

• Air intrusion; hydraulic cylinder end cover seal is pressed too tight or too loose; piston rod and piston are not centered; piston rod full length or partial bending; the installation position of the hydraulic cylinder is offset; hydraulic cylinder corrosion, hair pulling; double piston rod ends screwed too tight, so that the concentricity is not good.

• Rely on the gap seal piston and hydraulic cylinder gap, throttle valve lost throttling effect; end buffer check valve failure, the buffer does not work.

• Hydraulic cylinder and piston with too much clearance or O-ring damage, resulting in high and low pressure cavity interoperability; cylinder end of the oil seal is too tight or piston rod bending, so that the friction or resistance increased; too much leakage; oil temperature is too high, viscosity decreases, the seal which relies on gap or poor-quality cylinder line speed becomes slower. If the two ends of the hydraulic cylinder high and low pressure oil chamber interchange, the running speed gradually slows down until stop.

Exclusion Method

• Add exhaust device；adjust the seal so that it is not tight and not loose, to ensure that the piston rod can be pulled back and forth smoothly by hand without leakage; correct the concentricity of them; straighten the piston rod; check the parallelism of the hydraulic cylinder and guide rail and correct; boring repair, reassemble the piston; repair the rust and burrs in minor cases, serious cases must be bored; the screw should not be screwed too tightly, to keep the piston rod in its natural state.

• According to the provisions of the piston and hydraulic cylinder clearance, reduce leakage; correction of research and matching check valve and valve seat.

• Single with the piston or hydraulic cylinder clearance or replace the O-ring seal; boring to repair the bore of the hydraulic cylinder, with single piston; relax the oil seal to straighten the piston rod without oil leakage; find the leaky parts, tighten the joint across the board; analyze the cause of heat, try to cool down the heat, such as the seal gap is too large, then a single piston or install additional sealing rod.

Relief Valve of Hydraulic System

Failure Phenomenon

• Pressure fluctuations.

• Adjustment invalid.

• Severe oil leakage.

• Noise and vibration.

Failure Analysis

• Spring is bent or too soft; cone valve and valve seat contacts are not good; steel ball and the valve seat fit poorly; deformation or hairpulling of the slide valve.

• Spring breakage or leakage; damping hole blockage; slide valve stuck; reverse oil inlet and outlet; missing cone valve.

• Poor contact between the cone valve or steel ball and the valve seat; sliding valve and valve body with too large a gap; the pipe joint is not tightened; seal damage.

• Loose nut; spring deformation, not recovery; sliding valve with too tight; the main slide valve action is not good; cone valve wear; there is air in the center of the oil outlet path; flow rate exceeds the allowable value; resonance with other valves.

Exclusion Method

• Replace the spring; if the cone valve is new, that is, remove the adjustment nut to push the guide rod a few times to make good contact; or replace the cone valve; check the roundness of the steel ball, replace the steel ball, grinding the valve seat; replace or repair the slide valve.

• Check, replace or re-install the spring; unclog the damping hole; take out, check and trim; check the direction of oil source.

• Replace the cone valve or steel ball with a new one when it is worn out; check the spool and valve body clearance; tighten the coupling screw; check and replace the seal.

• Fasten the nut; check and replace the seal; repair and study the slide valve to make it flexible; check the concentricity of the slide valve and the shell; change the cone valve; exhaust air; replace the valve corresponding to the flow rate; slightly change the rated pressure value of the valve (such as the difference in the rated pressure value within 0.5Mpa, it is easy to resonate).

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