In the daily operation of hydraulic systems, internal leakage in hydraulic cylinders is often difficult to detect in time. Once the system fails, this issue is frequently overlooked.
Today, we will explore effective methods to check for internal leakage in hydraulic cylinders and share practical solutions to resolve it.
What Is Internal Leakage in Hydraulic Cylinders?
Internal leakage refers to hydraulic oil leaking from the high-pressure chamber of a hydraulic component into the low-pressure chamber. The entire leakage process happens inside the hydraulic cylinder, which is why it is called internal leakage.
Based on the structural characteristics of hydraulic cylinders, internal leakage primarily occurs in two areas:
1. Between the piston and the inner wall of the cylinder
2. At the connection between the piston rod and the piston
The seal between the piston and the cylinder wall is a dynamic seal. Internal leakage in this area can be caused by:
- Improper selection of sealing elements
- Unreasonable structure or size at the installation site
- Poor installation quality
- Damaged or detached seals
- Misalignment between the piston and the piston rod
- Excessive working temperature or pressure
- Contaminated hydraulic oil
The seal at the piston rod and piston connection is a static seal. If the sealing structure is poorly designed or the seal is wrongly chosen, leakage can also occur here.
How to Determine If a Hydraulic Cylinder Has Internal Leakage?
So, how can we determine whether a hydraulic cylinder is experiencing internal leakage? Here are three methods:
Method 1: On-Site Observation
At the production site, use your senses—listen, smell, and observe—to check whether the cylinder is operating properly. Signs of leakage may include:
- Failure to move
- Slow movement
- Noticeable oil temperature changes
- Vibrations or abnormal noise
Based on your experience, these signs can help you judge whether internal leakage is present.
Method 2: Pressure Testing
1. Fully extend the hydraulic cylinder.
2. Ensure there is no load on the cylinder so it won’t retract on its own.
3. Turn off the machine and disconnect the oil pipe from the rod chamber.
4 . Press the switch to extend the cylinder and increase pressure.
- If oil flows out from the rod chamber port, internal leakage is confirmed.
- If no oil appears, there is no internal leakage.
Note: If the cylinder cannot reach its end position, the issue is more complex.
Check the directional valve and the relief valve first to rule out their internal leakage. Only after confirming they are functioning correctly can you determine whether the cylinder itself is leaking internally.
If possible, disassemble the hydraulic cylinder for a direct inspection. You can also
- Install pressure gauges and ball valves on the ports at both ends of the cylinder.
- Apply pressure and check the pressure drop based on national standards to determine if internal leakage exists.
Method 3: Drain and Load Test
- Remove the return oil pipe from the upper chamber oil port and connect it to an oil basin.
- Raise the piston to its highest point to drain oil from the upper chamber.
- Operate the directional control valve several times.
- Since the upper chamber has no oil replenishment, filling the lower chamber with oil will raise the piston.
- If a large amount of oil flows out from the upper chamber, internal leakage between the upper and lower chambers is present.
Causes and Solutions for Internal Leakage in Hydraulic Cylinders
1. Hydraulic System Issues
If internal leakage occurs, first:
- Check whether the hydraulic system is functioning normally.
- Inspect all suction pipe joints and connections for leakage.
- Avoid overtightening hose joints, as this may deform them and increase leakage.
Use the manufacturer’s recommended torque values to ensure a reliable seal without damaging the fittings or seals.
Also, consider the following:
- Aging or worn high-pressure oil pipes
- Loose pipe fittings
In such cases, repair or replace the necessary parts.
2. Seal Issues
Hydraulic cylinders have front and rear sealing structures.
If leakage occurs when the front end extends, it may be due to
- Aging
- Damage
- Blockage of front-end seals
Usually, this involves piston seals or static seals.
Over time, even minor internal leakage will worsen, leading to:
- System overheating
- Failure of other components
In this case, disassemble the cylinder and replace the seals that are severely worn.
3. Lubrication Problems
Hydraulic cylinders require proper lubrication during telescopic movement.
Poor lubrication leads to:
- Seal wear
- Aging
- Oil leakage
Thus, during maintenance, make sure to strengthen lubrication protection.
In addition, the warning signs of internal leakage.
Additional symptoms of internal leakage include:
- Air bubbles in hydraulic oil
- Unstable hydraulic system or creeping movements
- Overheating
- Increased tank pressure
- Increased pump noise
Conclusion
Internal leakage in hydraulic cylinders should not be ignored.
By mastering effective inspection methods and implementing preventive measures, you can reduce or avoid internal leakage.
We recommend regular inspection and maintenance of hydraulic cylinders to ensure stable hydraulic system performance and extend service life.
