Leakage of the hydraulic pressure relief valve can lead to abnormal system pressure, fluid loss, and unplanned shutdowns. If you are an operations engineer or procurement specialist, identifying the cause of the leak and performing timely repairs is crucial to making sure continuous equipment operation.
Common Signs of Pressure Relief Valve Leaking
Oil Stains and Dripping on the Exterior of the Valve Body
External oil leakage is the most obvious sign of a pressure relief valve leaking. You may notice oil seeping around the adjustment screw, dripping at the interface, forming stains near the valve body, and accumulating on the ground. This will waste hydraulic oil and increase your operating costs.
After prolonged leakage, dust and metal particles are likely to adhere to the valve body surface, further accelerating the aging of the seals. In high-temperature environments, there is even a risk of fire.
Abnormal System Pressure
When the pressure relief valve has internal leakage, the high-pressure oil will abnormally flow from the gap between the valve core and the valve seat to the low-pressure return oil chamber. You will observe that the pressure gauge pointer keeps swinging, the pressure rises slowly, or the system pressure repeatedly fluctuates around the set value.
This will affect the equipment stability and also cause the pump to remain in a high-load state for a long time. Especially in injection molding machines, hydraulic machines, construction machinery and industrial production lines, pressure fluctuations will directly affect the operation accuracy and your production rhythm.
Slow or Weak Actuator Action
When internal leakage occurs in the hydraulic pressure relief valve, some high-pressure oil will flow back to the oil tank in advance. This results in the system being unable to establish sufficient working pressure.
You may notice that the hydraulic cylinder operates more slowly, the lifting equipment is ineffective, the clamping force decreases, and heavy-load operations become difficult. This situation is particularly evident in high-load equipment, such as hydraulic lifting platforms, forging equipment, and large construction machinery.
At this time, the equipment can still operate, but the production efficiency has begun to decline. If you continue to use the equipment until the hydraulic pump overheats or the actuator fails to operate before stopping for repairs, it will result in higher maintenance costs.
Abnormal Increase in Hydraulic Oil Temperature
When the pressure relief valve fails to close completely, some hydraulic oil will continuously pass through the pressure relief circuit and form an internal circulation. The hydraulic energy cannot be converted into mechanical output but keeps being converted into heat.
You will find that the temperature of the oil tank remains consistently high, and the load on the cooling system increases. Long-term high temperatures will cause the viscosity of the hydraulic oil to decrease, further aggravating the leakage. It will also accelerate the aging of the seals, resulting in more maintenance costs for you.
Abnormal Noise and Vibration
When the hydraulic system is operating normally, there is usually only a smooth “buzzing” sound. If you hear a sharp “sizzling” sound, “howling” sound or irregular “vibrating” sound near the pressure relief valve, this might indicate a leakage. In severe cases, there may also be vibrations of the valve body or the pipeline, affecting the stability of the entire system.
Reasons for Pressure Relief Valve Leaking
Long-Term System Overpressure Operation
The function of the pressure relief valve is to limit the maximum pressure of the system. When the system pressure exceeds the set value of the valve, the valve will automatically open to return the oil and relieve the pressure.
If the overpressure condition persists for a long time, the valve will continuously withstand impacts, ultimately leading to wear of the sealing surface, fatigue of the spring, and leakage. Excessive pump flow, stuck downstream actuators, poor return oil, and failure of the pressure compensation system can all cause the system to overpressure.
If you only replace the pressure relief valve but fail to solve the long-term system overpressure problem, the pressure relief valve leaking is likely to recur.
Hydraulic Oil Contamination
Metal shavings, oil sludge, dust in the air, and deposits formed by aged oil all may enter the gap between the valve core and the valve seat along with the hydraulic oil.
Large particles of impurities will directly get stuck in the tiny gap between the valve core and the valve body, or get trapped on the sealing surface of the valve seat, preventing the pressure relief valve from closing completely.
Wear of the Valve Core and the Valve Seat Sealing Surface
During the frequent pressure relief process, the valve core and valve seat will be constantly subjected to the scouring effect of high-speed oil flow. When there are pressure shocks or frequent start-stop operations in the system, the wear rate will increase.
When the sealing surface shows scratches, pitting, or local deformation, internal leakage will still occur after the valve is closed.
Spring Fatigue
The hydraulic pressure relief valve usually relies on springs to maintain the set pressure. As the operating time increases, the springs will gradually fatigue, resulting in a decrease in the opening pressure. Some older equipment may also encounter problems such as loosening of the pressure regulating screw or wear of the pressure regulating mechanism.
Troubleshooting and Repair of Pressure Relief Valve Leakage Faults
Necessary Preparations Before the Investigation
Firstly, you need to carry out proper system security processing. Shut off the power supply of the equipment first, completely release the residual oil pressure inside the pipeline, and ensure that the pressure gauge returns to zero.
At the same time, take measures to prevent power failure from causing the equipment to start accidentally. These simple preparatory steps can significantly reduce the operational risks during the maintenance process.
Distinguish Leakage Types
By visual inspection, you can quickly determine whether the leakage is external or internal.
External leakage: You will see that the oil is seeping out from the threaded interface, the end cover sealing ring or the joint surface of the valve body.
Internal leakage: Internal leakage is relatively concealed. You can quickly confirm it through a pressure stabilization test. If the pressure drops rapidly after the system maintains pressure, then you can determine that there is leakage inside the valve.
External Leakage Repair
Excessive leakage from the pressure relief valve is usually caused by aging seals, loose bolts, and damaged valve body interfaces. Long-term operation of the equipment can easily lead to bolt loosening.
You can first tighten the valve body fixing bolts and pipe connections one by one. If there is still leakage after tightening, you can replace the valve body end cover, the O-ring at the pressure-regulating position, and the sealing gasket. If you find cracks on the valve body surface, you need to replace the entire valve directly.
Internal Leakage Repair
After confirming the existence of an internal leak, you need to disassemble the valve body. Clean the oil sludge and metal impurities inside the valve core and valve chamber.
Check if there are scratches, pitting or continuous grooves on the sealing surface of the valve core and valve seat. For minor damage, you can use a grinding disc combined with grinding paste for repair. For deep damages, you need to replace the parts.
At the same time, check the internal pressure-regulating spring. If the spring deforms or its elasticity decreases, it needs to be replaced in time.
If your hydraulic pressure relief valve is of the pilot type, you also need to check the damping hole to avoid blockage.
Resetting the Pressure
After reinstalling the pressure relief valve back into the system, you still need to re-adjust the pressure. Connect the calibrated pressure gauge, start the system, and slowly adjust the pressure control handle.
Let the system run for several seconds after each adjustment and observe the pressure gauge reading. Once the set value is reached, tighten the locking nut and recheck if the pressure is stable. During the entire adjustment process, do not make large and rapid rotations to avoid excessive pressure surges.
Whole Machine Testing
After adjusting the pressure, you cannot immediately put the equipment into full-load operation. You need to start the equipment without load first, gradually increase the system pressure, and observe whether the pressure gauge can maintain the set value stably.
After running for a period of time, check again whether there is any oil leakage on the valve body surface, whether the system pressure is stable, whether the valve is properly opened, and whether the oil temperature is normal.
How to Prevent a Pressure Relief Valve from Leaking?
Regularly Monitor the System Pressure
For large hydraulic stations, injection molding equipment and construction machinery, many pressure relief valves leak due to the long-term existence of pressure fluctuations and shocks in the system.
It is recommended that you regularly monitor the actual working pressure, peak pressure, pump outlet pressure and pressure relief valve opening pressure of the system. Establishing stable pressure monitoring can help you detect pressure relief valve leaks in advance.
Keep Hydraulic Oil Clean
Based on the operating conditions of the equipment, you need to conduct regular monitoring of the cleanliness of the oil and replace the aged hydraulic oil promptly. When changing the oil, you must also clean the oil tank and the pipelines simultaneously to prevent secondary pollution caused by residual contaminants.
When refilling the oil, use an oil refilling device with a filtering function to avoid the mixture of air and contaminants.
Use High-Precision Filters
The gap between the valve core is extremely small. Even tiny particles can cause the valve core to get stuck or the seal to fail. Once contaminants enter the system, it will lead to internal leakage of the valve, accelerate the wear of the pump, actuator and control valve, and result in higher costs for you.
You can install filters with a filtration accuracy of ≤ 10μm at the pump outlet and return oil line. You can also add a bypass circulation filtration system.
Regularly Inspect the Pressure Relief Valve
Actively identifying potential problems can prevent minor issues from escalating into major failures. Before each startup or after use, you can check whether there is any oil overflowing from the valve body, or if there is any deformation or cracks on the outside of the valve body.
Depending on the frequency of equipment usage, you can conduct a pressure relief valve function test once every quarter or half a year. For example, use a calibrated pressure gauge to verify the set pressure of the pressure relief valve, and conduct a pressure holding test to observe the rate at which the system pressure drops.
Every year, you can also disassemble the pressure relief valve for cleaning, inspection, and replacement of old components.
Establish and Maintain Records
You can establish a maintenance logbook. After each maintenance, record the maintenance date, the problem, the handling measures, and the reset pressure value. This makes it easier for you to optimize your maintenance plan.
FAQs
There Is a Small Amount of Oil Leakage from the Pilot Port of the Pilot-Operated Relief Valve. Is This a Sign of a Leak?
During the pressure regulation stage of the pilot-operated relief valve, a very small amount of oil will flow out from the pilot port. This is a normal condition. You can further distinguish it based on the operating status.
If the oil leakage completely disappears after the equipment is running stably, no action is required. If there is still continuous oil leakage even in the no-load and pressure-stabilizing state, or if the oil volume increases, it indicates that the valve is leaking. You need to inspect the sealing components and mating surfaces of the valve.
Which Parameters Should Be Considered When Selecting a Pressure Relief Valve to Prevent Leakage in the Later Stage?
When choosing a pressure relief valve, merely focusing on the pressure and flow parameters is not sufficient. You should also pay attention to the processing accuracy and surface treatment process of the valve core and valve seat. The sealing surface produced by high-precision grinding has a stronger anti-wear ability. At the same time, you need to select compatible seals based on the working temperature and the type of hydraulic oil.
To Make Sure That the Purchased Hydraulic Pressure Relief Valve Does Not Leak Prematurely, Which Standards Do I Need to Check?
It is recommended that you prioritize checking the ISO 4413, CE, and ASME standards certifications. ISO 4413 mainly stipulates the requirements for safety and pressure control in hydraulic systems. It can help you determine whether the valve meets the industrial standards in terms of sealing, pressure resistance, and long-term operational stability.
For export projects or high-pressure conditions, it is also necessary to confirm whether the manufacturer has complete records of pressure tests and leak tests. Because many pressure relief valve leakage problems are caused by insufficient manufacturing accuracy and testing standards.
Can hydraulic oil type affect the Pressure Relief Valve leaking?
Yes. When the oil is too thin, internal leakage is more likely to occur. After the hydraulic oil ages at high temperatures, it is prone to form deposits, accelerating the wear of the valve core and valve seat. Many customers have started to experience hydraulic pressure relief valve leakage after changing to a different brand of oil.
This is because the parameters of the new oil do not match the design of their systems. Therefore, in addition to the viscosity grade of the hydraulic oil, you also need to confirm the oil’s anti-wear performance, antioxidant capacity, and compatibility with sealing materials.
Do the Relief Valves of Different Pressure Ratings Have Any Differences in the Selection of Components to Prevent Leakage?
Yes. The low-pressure relief valve can be used with conventional standard seals. If your equipment is used under high pressure, then you need to choose sealing rings, gaskets, etc. that are resistant to high pressure.
Under high-pressure conditions, the strength requirements for the pressure-regulating spring and the valve core are even higher. Mixing low-pressure components will increase the probability of pressure relief valve leakage.
Final Thoughts
Now, it is easy for you to notice that the most cost-effective way to deal with pressure relief valve leakage is always proactive maintenance rather than emergency repair. Every time a pressure relief valve leaks and causes a shutdown, it will directly disrupt the production rhythm and incur additional maintenance costs. If you have any questions about the pressure relief valve leakage or need to make a purchase, please feel free to contact us.
