Analysis and Troubleshooting of Common Hydraulic System Faults
Release Date:2026-06-09 Source: Views:96
I. Working Principle
Hydraulic transmission is a transmission mode that uses liquid as the working medium to realize the required movement of actuators through energy conversion. First, the hydraulic pump converts the mechanical energy of an electric motor (or other prime movers) into pressure energy of the liquid. Then, the hydraulic cylinder (or hydraulic motor) converts the liquid pressure energy back into mechanical energy to drive the load for movement.
II. Composition of Hydraulic Systems
A hydraulic transmission system generally consists of the following five parts:
1. Power Unit
Its function is to convert mechanical energy provided by the electric motor (or other prime movers) into liquid pressure energy. Simply put, it is a device that supplies pressurized oil to the system, such as various types of hydraulic pumps.
2. Control and Regulation Unit
It includes pressure control valves, flow control valves and directional control valves. These components control and regulate the pressure, flow rate and flow direction of the hydraulic fluid in the system, so as to meet the requirements of force (or torque), speed (or rotational speed) and movement direction (or motion cycle) of working components.
3. Actuating Unit
It converts liquid pressure energy into mechanical energy to drive the movement of working parts, mainly including hydraulic cylinders and hydraulic motors.
4. Automatic Control Unit
It mainly refers to electrical control devices.
5. Auxiliary Unit
Components other than the above four categories, including oil tanks, tubing, manifold blocks, oil filters, accumulators, pressure gauges, heaters, coolers and so on. They are indispensable and play a vital role in ensuring the reliability and stability of hydraulic system operation.
III. Hydraulic Cylinders
A hydraulic cylinder is an actuator that converts hydraulic energy into mechanical energy. Common faults of hydraulic cylinders include creeping, external leakage, mechanical jamming, air intake and impact.
1. Analysis and Troubleshooting of Cylinder Creeping
(1) Air trapped inside the cylinder or pipelines
Solutions: Install exhaust devices; if no exhaust device is available, run the hydraulic system back and forth several times at full stroke to force air out; seal the system and all pipelines.
(2) Negative pressure formed at certain positions of the cylinder
Solutions: Locate the negative pressure points of the cylinder for sealing and conduct air bleeding.
(3) Over-tight compression of sealing rings
Solutions: Adjust the sealing rings to a moderate tightness so that the piston rod can be pushed and pulled smoothly by hand.
(4) Misalignment between piston and piston rod
Solutions: Assemble the two parts together, calibrate on V-blocks to control the concentricity error within 0.04 mm, or replace with a new piston.
(5) Bent piston rod
Solutions: Straighten the single piston rod or the assembly together with the piston on V-blocks using a press, and verify straightness with a dial indicator.
(6) Excessively tight guide rails/sliders or misalignment between guide rails and cylinder
Solutions: Adjust the tightness of guide rail pressing strips to guarantee both precision of moving parts and low sliding resistance. If adjustment fails, inspect the parallelism between the cylinder and guide rails and scrape the contact surfaces for correction.
(7) Over-tightened lock nuts at both ends of the piston rod
Solutions: Adjust nut tightness to keep the piston rod in a free natural state.
(8) Scratches, severe local wear or corrosion on cylinder inner wall or piston surface
Solutions: Bore the cylinder bore and refit a matched new piston.
2. Analysis and Troubleshooting of Cylinder Impact Faults
(1) Absence of buffer devices
Solutions: Extend the reversing time to more than 0.2 seconds to reduce the moving speed of the cylinder; add buffer devices.
(2) Excessive clearance between buffer plunger and buffer hole
Solutions: Replace the buffer plunger or install a bushing in the hole to bring the clearance within the specified range; inspect the throttle valve.
(3) Reversed one-way valve for end buffering
Solutions: Repair and lap-fit the one-way valve and its valve seat, or replace the valve assembly.
3. Analysis and Troubleshooting of Cylinder External Leakage
(1) Surface damage on the piston rod
Solution: Repair the damaged piston rod surface.
(2) Edge damage or aging of sealing rings
Solution: Replace the worn or aged sealing rings.
(3) Poor sealing at pipe joints
Solution: Check sealing rings and contact surfaces for scratches, then repair or replace defective parts.
(4) Loose sealing at the cylinder head
Solution: Check the machining accuracy of contact surfaces and aging status of seals, replace or repair components in a timely manner.
(5) Sealing ring damage caused by local high temperature from adiabatic compression of trapped gas due to inadequate air bleeding
Solution: Inspect or add exhaust devices and perform regular air bleeding.
(6) Poor sealing at buffer assemblies
Solution: Check the machining precision of piston rod contact surfaces and aging of seals, replace or trim seals promptly.
4. Analysis and Troubleshooting of Cylinder Internal Leakage
(1) Excessive fit clearance caused by wear of cylinder bore and piston
Solution: If the piston is heavily worn, bore the cylinder bore, turn down the piston outer diameter, machine several grooves for installing sealing rings, or fit a brand-new piston.
(2) Scratched or aged sealing rings on the piston
Solution: Replace damaged or aged sealing rings immediately.
(3) Tilt or eccentric wear of the piston resulting from misaligned installation between piston and cylinder barrel or eccentric load
Solution: Inspect the concentricity of the cylinder barrel, piston and piston rod hole of the cylinder head, then realign and trim mating surfaces.
(4) Barrel-shaped deformation of cylinder bore due to poor straightness in machining or partial wear
Solution: Rebore the cylinder bore and match a new piston.
5. Abnormal Sound and Noise
Cause: Adiabatic compression of air at the lower part of the piston
Solution: Run the piston slowly back and forth multiple times, fully reaching the top dead center each stroke to discharge internal air. This will eliminate severe noise and prevent sealing ring burnout.
IV. Hydraulic Control Valves
Hydraulic control valves are control and regulation elements in hydraulic transmission systems. They govern the flow direction, pressure and flow rate of hydraulic oil to meet the pressure, direction and speed requirements of actuators, so that the actuating unit drives the load to complete predetermined actions.
1. Performance Requirements for Hydraulic Valves
The main performance requirements for hydraulic valves in a hydraulic system are as follows:
(1) Sensitive action, reliable operation, low impact and vibration during service, and long service life.
(2) Low pressure loss when hydraulic oil flows through the valve, excellent sealing performance, minimal internal leakage and zero external leakage.
(3) Compact structure, convenient installation, maintenance and adjustment, and good versatility.
2. Classification of Hydraulic Valves
(1) Pressure Control Valves (Pressure Valves for short)
Used to control system pressure to satisfy the force (or torque) demand of actuators, including relief valves, pressure reducing valves, sequence valves, pressure relays, etc.
(2) Directional Control Valves (Directional Valves for short)
Used to control the flow direction of hydraulic oil to meet the movement direction requirements of actuators, including check valves, directional valves, etc.
(3) Flow Control Valves (Flow Valves for short)
Used to regulate fluid flow rate to control the moving speed of actuators, including throttle valves, flow control valves, etc.
(4) Compound Valves (Multi-function Valves)
Control two or all three parameters (direction, pressure and flow rate) of the hydraulic system. For example, a one-way pressure reducing valve can control both the flow direction and pressure of hydraulic fluid simultaneously.
3. Analysis and Troubleshooting of Common Relief Valve Faults
Taking the relief valve as a typical example of hydraulic valves for brief introduction.
I. Working Principle
Hydraulic transmission is a transmission mode that uses liquid as the working medium to realize the required movement of actuators through energy conversion. First, the hydraulic pump converts the mechanical energy of an electric motor (or other prime movers) into pressure energy of the liquid. Then, the hydraulic cylinder (or hydraulic motor) converts the liquid pressure energy back into mechanical energy to drive the load for movement.
II. Composition of Hydraulic Systems
A hydraulic transmission system generally consists of the following five parts:
1. Power Unit
Its function is to convert mechanical energy provided by the electric motor (or other prime movers) into liquid pressure energy. Simply put, it is a device that supplies pressurized oil to the system, such as various types of hydraulic pumps.
2. Control and Regulation Unit
It includes pressure control valves, flow control valves and directional control valves. These components control and regulate the pressure, flow rate and flow direction of the hydraulic fluid in the system, so as to meet the requirements of force (or torque), speed (or rotational speed) and movement direction (or motion cycle) of working components.
3. Actuating Unit
It converts liquid pressure energy into mechanical energy to drive the movement of working parts, mainly including hydraulic cylinders and hydraulic motors.
4. Automatic Control Unit
It mainly refers to electrical control devices.
5. Auxiliary Unit
Components other than the above four categories, including oil tanks, tubing, manifold blocks, oil filters, accumulators, pressure gauges, heaters, coolers and so on. They are indispensable and play a vital role in ensuring the reliability and stability of hydraulic system operation.
III. Hydraulic Cylinders
A hydraulic cylinder is an actuator that converts hydraulic energy into mechanical energy. Common faults of hydraulic cylinders include creeping, external leakage, mechanical jamming, air intake and impact.
1. Analysis and Troubleshooting of Cylinder Creeping
(1) Air trapped inside the cylinder or pipelines
Solutions: Install exhaust devices; if no exhaust device is available, run the hydraulic system back and forth several times at full stroke to force air out; seal the system and all pipelines.
(2) Negative pressure formed at certain positions of the cylinder
Solutions: Locate the negative pressure points of the cylinder for sealing and conduct air bleeding.
(3) Over-tight compression of sealing rings
Solutions: Adjust the sealing rings to a moderate tightness so that the piston rod can be pushed and pulled smoothly by hand.
(4) Misalignment between piston and piston rod
Solutions: Assemble the two parts together, calibrate on V-blocks to control the concentricity error within 0.04 mm, or replace with a new piston.
(5) Bent piston rod
Solutions: Straighten the single piston rod or the assembly together with the piston on V-blocks using a press, and verify straightness with a dial indicator.
(6) Excessively tight guide rails/sliders or misalignment between guide rails and cylinder
Solutions: Adjust the tightness of guide rail pressing strips to guarantee both precision of moving parts and low sliding resistance. If adjustment fails, inspect the parallelism between the cylinder and guide rails and scrape the contact surfaces for correction.
(7) Over-tightened lock nuts at both ends of the piston rod
Solutions: Adjust nut tightness to keep the piston rod in a free natural state.
(8) Scratches, severe local wear or corrosion on cylinder inner wall or piston surface
Solutions: Bore the cylinder bore and refit a matched new piston.
2. Analysis and Troubleshooting of Cylinder Impact Faults
(1) Absence of buffer devices
Solutions: Extend the reversing time to more than 0.2 seconds to reduce the moving speed of the cylinder; add buffer devices.
(2) Excessive clearance between buffer plunger and buffer hole
Solutions: Replace the buffer plunger or install a bushing in the hole to bring the clearance within the specified range; inspect the throttle valve.
(3) Reversed one-way valve for end buffering
Solutions: Repair and lap-fit the one-way valve and its valve seat, or replace the valve assembly.
3. Analysis and Troubleshooting of Cylinder External Leakage
(1) Surface damage on the piston rod
Solution: Repair the damaged piston rod surface.
(2) Edge damage or aging of sealing rings
Solution: Replace the worn or aged sealing rings.
(3) Poor sealing at pipe joints
Solution: Check sealing rings and contact surfaces for scratches, then repair or replace defective parts.
(4) Loose sealing at the cylinder head
Solution: Check the machining accuracy of contact surfaces and aging status of seals, replace or repair components in a timely manner.
(5) Sealing ring damage caused by local high temperature from adiabatic compression of trapped gas due to inadequate air bleeding
Solution: Inspect or add exhaust devices and perform regular air bleeding.
(6) Poor sealing at buffer assemblies
Solution: Check the machining precision of piston rod contact surfaces and aging of seals, replace or trim seals promptly.
4. Analysis and Troubleshooting of Cylinder Internal Leakage
(1) Excessive fit clearance caused by wear of cylinder bore and piston
Solution: If the piston is heavily worn, bore the cylinder bore, turn down the piston outer diameter, machine several grooves for installing sealing rings, or fit a brand-new piston.
(2) Scratched or aged sealing rings on the piston
Solution: Replace damaged or aged sealing rings immediately.
(3) Tilt or eccentric wear of the piston resulting from misaligned installation between piston and cylinder barrel or eccentric load
Solution: Inspect the concentricity of the cylinder barrel, piston and piston rod hole of the cylinder head, then realign and trim mating surfaces.
(4) Barrel-shaped deformation of cylinder bore due to poor straightness in machining or partial wear
Solution: Rebore the cylinder bore and match a new piston.
5. Abnormal Sound and Noise
Cause: Adiabatic compression of air at the lower part of the piston
Solution: Run the piston slowly back and forth multiple times, fully reaching the top dead center each stroke to discharge internal air. This will eliminate severe noise and prevent sealing ring burnout.
IV. Hydraulic Control Valves
Hydraulic control valves are control and regulation elements in hydraulic transmission systems. They govern the flow direction, pressure and flow rate of hydraulic oil to meet the pressure, direction and speed requirements of actuators, so that the actuating unit drives the load to complete predetermined actions.
1. Performance Requirements for Hydraulic Valves
The main performance requirements for hydraulic valves in a hydraulic system are as follows:
(1) Sensitive action, reliable operation, low impact and vibration during service, and long service life.
(2) Low pressure loss when hydraulic oil flows through the valve, excellent sealing performance, minimal internal leakage and zero external leakage.
(3) Compact structure, convenient installation, maintenance and adjustment, and good versatility.
2. Classification of Hydraulic Valves
(1) Pressure Control Valves (Pressure Valves for short)
Used to control system pressure to satisfy the force (or torque) demand of actuators, including relief valves, pressure reducing valves, sequence valves, pressure relays, etc.
(2) Directional Control Valves (Directional Valves for short)
Used to control the flow direction of hydraulic oil to meet the movement direction requirements of actuators, including check valves, directional valves, etc.
(3) Flow Control Valves (Flow Valves for short)
Used to regulate fluid flow rate to control the moving speed of actuators, including throttle valves, flow control valves, etc.
(4) Compound Valves (Multi-function Valves)
Control two or all three parameters (direction, pressure and flow rate) of the hydraulic system. For example, a one-way pressure reducing valve can control both the flow direction and pressure of hydraulic fluid simultaneously.
3. Analysis and Troubleshooting of Common Relief Valve Faults
Taking the relief valve as a typical example of hydraulic valves for brief introduction.
