Common faults and troubleshooting of superimposed relief valves

The superimposed relief valve is a hydraulic control element that integrates the overflow function with the superimposed valve plate. It is widely used in hydraulic systems for pressure regulation, overload protection and system unloading. Its common faults are usually related to pressure instability, leakage, abnormal noise or failure of action. The following details are explained in detail from three aspects: failure phenomenon, cause analysis and removal methods:

1. Pressure unstable (system pressure fluctuates or cannot reach the set value)

Fault phenomenon

The system pressure is fluctuating and low, and cannot be stabilized at the set value.

The actuator (such as a hydraulic cylinder) acts slowly or shakes.

Cause analysis

Problem of pressure regulating spring The spring is fatigued or broken, resulting in insufficient preload.

The spring seat is loose or stuck, affecting pressure regulation.

Spool malfunctions The valve core is worn or woven, causing leakage or stagnation.

The conical surface of the valve core is not tightly sealed, causing internal leakage.

The damping hole blocks the damping hole is blocked by impurities in the oil, affecting pressure feedback.

Oil contaminates the oil to mix particles, moisture or air, causing the valve core to be blocked or cavitated.

Remote control port problem Remote control port pressure fluctuates (such as failure of external pressure regulating valve).

Troubleshooting

Check that the pressure regulating spring replaces the fatigued or broken spring and adjust the spring seat to the correct position.

Clean or replace the valve core and disassemble the valve body, clean the valve core and valve seat with hydraulic oil, repair the wear surface or replace new parts.

Clean the damping holes with fine steel wire or compressed air to clear the damping holes to ensure smooth oil circulation.

Filter or replace the oil and replace the clean hydraulic oil, and install an oil filter to prevent contamination.

Check the remote control port to confirm that the external pressure regulating valve is working properly and eliminate leakage or blockage of the remote control port.

2. Leakage (external or internal leakage)

Fault phenomenon

Oil seeps out of the valve body joint surface, threaded connection or valve core.

System pressure cannot be established or continues to fall.

Cause analysis

The seals damage the O-ring, the combined seals are aging or damaged.

Valve body cracks or sand hole casting defects or long-term high pressure lead to cracks in the valve body.

The valve core and the valve seat are not matched with each other and the cone surface is worn or installed skewed, resulting in the seal failure.

The installation surface is uneven and there are scratches or dirt on the contact surface between the valve plate and the bottom plate.

Troubleshooting

When replacing the seal, use pressure-resistant and oil-resistant sealing materials (such as fluoroelastomer) and install them according to the specifications.

Repair or replace the valve body to repair minor cracks or repair epoxy resin. If it is severely damaged, replace the valve body.

Grind the valve core and the valve seat with abrasive paste to pair the cone surface to ensure sealing.

Clean the installation surface and polish the contact surface with oil and stone to remove burrs and dirt, apply hydraulic oil and reinstall it.

3. Noise abnormality (vibration or howling)

Fault phenomenon

The overflow valve emits high-frequency vibration or harsh noise when it is working.

The system pressure gauge pointer swings violently.

Cause analysis

The hydraulic impact valve core opens/closes too quickly, causing a sudden change in pressure.

Air pocket phenomenon: Air is mixed into the oil, forming bubbles in the low-pressure area and rupture.

The valve core is stuck and the valve core is inflexible, causing mechanical vibration.

If the valve body resonates with the pipeline incorrectly, or the fixing bolts are loose.

Troubleshooting

Adjust dynamic performance Add an accumulator in front of the valve to absorb pressure shock; or use a pilot relief valve with damping instead.

Exhaust the air to check the oil level of the oil tank to ensure that the oil return pipe is immersed below the oil level; loosen the valve body exhaust screw to exhaust.

Clean the valve core and disassemble the valve body, clean the valve core with hydraulic oil and apply grease.

Strengthen and install fastening valve body fixing bolts, and add shock absorbing brackets to the pipeline.

4. Movement failure (cannot be turned on or off)

Fault phenomenon

The system pressure exceeds the set value but the relief valve does not open (overload protection fails).

When the system pressure does not reach the set value, the overflow valve is opened in advance (pressure cannot be built).

Cause analysis

The pilot valve fails. The pilot valve core is stuck or the spring breaks, causing the main valve to be unable to operate.

The main valve core is stuck in oil contamination or the valve core is deformed, making the main valve core unable to move.

The pressure regulating handle is loose and the pressure regulating screw is not locked, causing the pressure set value to drift.

The coil is burned or the wiring is loose, causing the solenoid to be unable to be connected.

Troubleshooting

Maintain the pilot valve Clean the pilot valve core and replace the damaged spring or seal.

Disassemble the main valve and disassemble the main valve body to repair or replace the stuck valve core.

Lock the pressure regulating handle and re-adjust the pressure regulating screw to prevent loosening.

Check the solenoid to measure the coil resistance, repair the wiring or replace the solenoid.

V. Other FAQs

Causes of excessive temperature: long-term overload, excessive oil viscosity or insufficient cooling.

Exclusion: Reduce the system load, select hydraulic oil with appropriate viscosity, and add cooling devices.

Reason for slow response: insufficient spring stiffness or excessive valve core mass.

Exclusion: Replace springs with greater stiffness and optimize the valve core structural design.

Maintenance recommendations

Regular inspection: Check the sealing, pressure setting and operation flexibility of the overflow valve every 3-6 months.

Oil management: Keep the oil clean (NAS below level 6) and replace the filter element regularly.

Avoid shock: Reduce pressure shock through soft start or buffer circuit when the system starts or stops.

Record data: Create equipment files, record pressure setting values, repair history and replacement parts information.

By systematically checking the above fault points, we can quickly locate the problems and take targeted measures to ensure the stable operation of the superimposed relief valve and extend the service life of the equipment.