The contaminants in the hydraulic system will not disappear automatically after a single oil change. Residual impurities will continue to damage hydraulic components, leading to repeated equipment shutdowns and higher maintenance costs. Follow this guide to flush your hydraulic system safely and keep long-term stable operation.
Why does the Hydraulic System Need to be Flushed?
Metal Particles will Continue to Damage the Entire Hydraulic System
Many hydraulic system failures are not caused by the sudden failure of a single component. Instead, they are the result of continuous wear due to the long-term circulation of contaminants.
After the hydraulic pump, hydraulic motor or hydraulic cylinder is damaged, a large amount of metal debris will enter the valve group, pipeline and actuator along with the hydraulic oil. If you do not thoroughly flush the hydraulic system and only replace the oil or pump, residual particles will continue to wear down the precision mating surfaces.
Finally, this leads to the re-damage of the new components. For construction machinery, hydraulic machines and injection molding equipment, such secondary failures often have higher maintenance costs than the initial repair.
Replacing the Oil cannot Remove the System’s Internal Contamination
You might think that simply replacing the hydraulic oil regularly will solve the pollution problem. However, there are a large number of areas within the hydraulic system that cannot be drained through ordinary oil discharge. For example, inside the cylinder, the valve block flow channels, the oil cooler, and the low-flow areas in long-distance pipelines.
These locations are prone to accumulating oil sludge, moisture, and wear particles. When new hydraulic oil enters the system, the remaining contaminants will re-enter the circuit, causing the new oil to be rapidly contaminated within a short period.
The true value of hydraulic system flushing lies in removing this hidden pollution, thereby reducing the risk of subsequent chain failures.
Contaminants can Shorten the Lifespan of the Hydraulic Components
Modern hydraulic systems have strict requirements for cleanliness. Precision components such as proportional valves, servo valves, and high-pressure piston pumps are highly sensitive to tiny particles.
When contaminants continue to circulate, they will gradually cause valve core sticking, unstable system pressure, slow or shaking actuator operation, increased pump noise, and rising oil temperature.
This will affect the equipment’s operational efficiency and shorten the overall service life of the hydraulic system. Compared to frequently replacing high-value hydraulic components, flushing your hydraulic system in advance is often a more cost-effective way to control risks.
Reduce Downtime and Operational Costs
For factories, mines, ports or construction sites, the cost of hydraulic system failure goes beyond just repair. The shutdown of hydraulic equipment can cause many chain effects, such as project delays, production line shutdowns, labor waiting costs, etc. These losses are usually much higher than the repair costs.
Correct hydraulic system flushing can reduce the uncertain risks in the subsequent operation of the equipment. It enables the equipment to operate in a more stable oil environment, reduces the failure rate, extends the lifespan of key hydraulic components, and lowers future maintenance costs.
If you need to rely on the continuous operation of hydraulic equipment, the value of this preventive maintenance is higher.
When is it Necessary to Flush the Hydraulic System?
When Using Brand-New Hydraulic Equipment
During the processes of pipe welding, valve body assembly, and pipe bending processing with the new hydraulic equipment, there will be some residual welding slag, metal debris, sealing residue and processing dust.
If you start running without system flushing, the tiny impurities will immediately wear down the precision valve core and the mating surface of the pump body. This can easily cause early failures of the new machine and also affect the original factory warranty rights of the equipment.
Pre-flushing of the system is an essential process for putting hydraulic equipment into use.
After a Major Equipment Overhaul or Replacement of Key Hydraulic Components
When your hydraulic equipment completes major repairs or replaces components such as hydraulic pumps, valves, cylinders, and the entire hydraulic pipeline, the process will bring in external dust and metal debris. Meanwhile, deteriorated sludge and wear particles will remain in the old circuit.
At this point, you must perform a full system flushing to remove residual pollutants from the circuit. This avoids rapid wear and tear caused by impurities after the new parts are put into use, and reduces your secondary maintenance costs and downtime losses.
Hydraulic Oil Deterioration
If you find that the hydraulic oil turns black and turbid, produces a pungent odor, emulsifies and turns white, or there is a large number of sediment impurities, gum and mud at the bottom of the hydraulic tank, it indicates that the oil has been severely oxidized, mixed with water and particles.
Only replacing hydraulic oil cannot clean the residual pollution in the dead corners of the pipeline. You need to perform a complete system flushing to thoroughly clean the entire hydraulic circuit.
When Replacing the Hydraulic Oil of Different Models and Brands
The additive formulas for different brands or types of hydraulic oil are different. Mixing them directly will cause chemical reactions. When using new hydraulic oil, you must thoroughly flush the entire hydraulic circuit. Emptying the remaining old oil can prevent compatibility issues between the new and old oils.
Hydraulic Equipment has Abnormal Operation but No Electrical Faults
When your hydraulic system malfunctions and electrical faults are eliminated, if there are still issues such as cylinder expansion and contraction jamming, operation shaking, it is mostly caused by impurities blocking the throttle hole and valve core clearance.
Timely flushing of the hydraulic system can remove blockages without disassembling the valve body and pipelines. This can quickly restore the equipment to normal operation, saving your time in troubleshooting and repair.
How to Flush the Hydraulic System? Step-by-Step Guide
Preparatory Work
First, you need to thoroughly inspect the system pipelines, joints, and seals for any damage or looseness. For precision and sensitive components such as servo valves and proportional valves, you should remove them or use temporary bypass pipelines for isolation in advance.
This is to prevent impurities from entering the valve body during the flushing process and causing wear.
Then, you need to prepare low-viscosity special flushing oil compatible with the system’s hydraulic oil model, new return oil filters, filtration and refilling equipment, and non-fibrous wiping cloths.
Step 1. Completely Drain the Old Hydraulic Oil
Before flushing, you need to drain as much of the old oil from the system as possible. It is better to do this when the hydraulic oil is warm, as it is easier to remove sludge and particles.
Besides the hydraulic tank, you should also focus on draining the hydraulic oil from components such as hydraulic cylinders, return pipelines, coolers, valve groups, and hydraulic motors.
Step 2. Clean the hydraulic tank
The interior of the hydraulic tank is usually one of the most contaminated areas. If you don’t thoroughly clean it, even after completing the system flushing, the deposits will still re-enter the circulation system.
Use a non-fibrous cloth to wipe the inner walls of the hydraulic tank thoroughly. You need to focus on cleaning the bottom of the tank, corners, magnetic adsorption areas, the area around the oil suction port, and the return oil area.
Step 3. Add the Flushing Oil and Exhaust Air
After completing the basic cleaning, you can add flushing oil to the hydraulic tank. The filling amount should be 70%-80% of the tank’s rated capacity. After adding the oil, start the hydraulic pump and operate it at low speed and low pressure.
Then you need to open all the exhaust valves of the system until the oil discharged from the exhaust valves has no bubbles or impurities and then close them. This is to prevent residual air in the system from causing cavitation and damaging the hydraulic pump.
Step 4. Circulating Flushing and Monitoring
Adjust the operating parameters of the hydraulic pump, and control the flow rate to make sure that the oil in the pipeline is in a turbulent state. Turbulence can better wash away the impurities adhering to the inner walls of the pipeline. At the same time, allow the actuator to fully operate.
During the cycle flushing process, you need to regularly test the flushing oil, such as changes in particle quantity, moisture content, and filter element clogging conditions. During the first test, you will find that the particle content is very high, which is normal. Because the internal deposition pollution in the system is being flushed out.
As the circulation and filtration continue, if the number of particles gradually decreases and the filter element no longer quickly clogs, this indicates that the internal pollution in the system is decreasing.
On the contrary, if the pollution in the flushing oil remains at a high level or the filter element quickly clogs after a long cycle, it means that there is still a large amount of pollutants in the system. At this time, you may need to repeat the flushing.
Step 5. Drain the Flushing Oil
After the flushing is completed, shut off the hydraulic pump and completely release the pressure. Open all the oil drain ports and thoroughly drain the flushing oil and the impurities flushed out. After draining, you should wipe the pipe interface and clean the inner wall of the hydraulic tank again to remove any remaining impurities.
Then, you must replace the new filter. Restore the previously isolated precision components and pipes to their original positions, making sure that the joints are tightly connected and sealed properly.
Step 6. Add New Hydraulic Oil
At this point, you can add new hydraulic oil that meets the requirements to the hydraulic tank. When refilling with new hydraulic oil, try to avoid the open pouring method. Using a filtered oil filling device can reduce the entry of external contaminants into the system.
Qualified Inspection after Flushing
Start the hydraulic equipment and let the system run without a load for a period of time. You need to observe whether the movement of the actuator is smooth and stable. At the same time, check the pressure and flow of the hydraulic system to make sure that the pressure is stable and the flow is normal without fluctuations.
Then you can test the cleanliness of the new hydraulic oil. If the number of particles in the new oil remains stable after running, it indicates that there are no obvious residual contaminants inside the system.
Common Mistakes in Hydraulic System Flushing
Replace the Special Flushing Oil with Ordinary Hydraulic Oil
The special flushing oil has a lower viscosity and better fluidity, which can quickly remove the oil sludge and tiny impurities adhering to the pipe’s dead corners. However, the ordinary hydraulic oil has a higher viscosity and cannot wash away the stubborn contaminants on the inner wall of the pipe.
During the subsequent operation of the equipment, these residual impurities will increase the probability of valve sticking and oil pump damage. This actually raises your maintenance costs.
No Isolation of Precision Components before Flushing
This is the most common mistake. The clearance between the precision components, such as servo valves and proportional valves, is only a few microns. During the flushing process, impurities will directly scrape against the valve core and sealing surface, causing wear and failure.
More importantly, this kind of damage is often irreversible. You will need to replace the expensive precision components in the future, and the production schedule may be affected due to prolonged equipment downtime.
Reusing of Filter Elements
If you clean the old filter element and reuse it, or forget to replace the filter element before adding new oil, it will cause impurities to re-enter the hydraulic circuit. You may need to invest more in maintenance costs in the later stage.
Not All Actuators were Activated During Flushing
For example, excavators, cranes, hydraulic lifting systems, etc., if the actuator is not allowed to complete the full stroke action, pollutants in many areas are not carried out. So during flushing, you must operate each hydraulic function multiple times and throughout the entire stroke.
Release the Flushing Oil after it has Cooled Down
After flushing, the oil temperature usually rises to around 50 ℃. At this temperature, pollutants remain suspended, and the oil has low viscosity and good fluidity.
If the oil is drained after it has cooled down, pollutants will re-settle to the bottom of the hydraulic tank and low-lying areas of the pipes during the cooling process. So you need to start draining the oil as soon as the flushing is finished.
FAQ
How often does the Hydraulic System Need to be Flushed?
The hydraulic system does not have a unified and fixed flushing cycle. The working environment, operating time, and pollution situation of different devices vary greatly. You need to make a judgment based on hydraulic oil analysis, filter element contamination, equipment operating status, etc.
How Long Does it Take to Flush the Hydraulic System?
The flushing time usually depends on the degree of contamination in the system. For a lightly contaminated system, a shorter cycle time may be sufficient. For large or severely contaminated hydraulic systems, the flushing process may require a longer time or even be carried out in stages.
A Lot of Foam Appears in the Oil During Flushing, Will it Affect the Flushing Effect?
Yes. The foam will occupy the pipeline space, which will lead to an unstable oil flow rate and be unable to form effective turbulence. This makes it difficult for impurities to be carried out. At the same time, when the foam breaks, it will wear the inner wall of the hydraulic pump, accelerating the aging of the seals.
Which Method is Better for Group Flushing or Overall Flushing?
Group flushing is suitable for large and complex hydraulic systems. It can accurately control the flow rate, pressure, and velocity of each pipeline, making sure that each section of the pipeline can form turbulence and thoroughly flush out impurities. It takes slightly longer.
Overall flushing is suitable for small and simple hydraulic systems. Its operation is simple and takes a short time.. You need to choose based on the condition of your hydraulic system.
Is There a Difference in Temperature During Flushing for Different Types of Flushing Oil?
Yes. Excessive temperature can accelerate oil oxidation, generate new gum and sludge, and increase system pollution. Low temperature will increase the viscosity of the flushing oil, making it difficult to effectively flush impurities.
The optimal flushing temperature for mineral oil flushing oil can be controlled between 45-55 ℃. Synthetic oil-based flushing oil has stronger heat resistance, and the optimal flushing temperature can be controlled at 50-60 ℃.
Final Thoughts
A thorough hydraulic system flushing can stabilize system operation, extend its lifespan, and reduce downtime losses and maintenance costs. If you need hydraulic system cleaning services or technical support, please feel free to contact us. We are committed to keeping your hydraulic system productive for a long time.
