The causes of hydraulic cylinder drift
Hydraulic systems certainly can have their challenges. If your system has stopped working, the first thing you want to do is to ensure your hoses are connected properly and that the couplings engage the way they should.
When problems arise, hydraulic drift – more specifically, hydraulic cylinder drift – is often the culprit. This is the result of unequal pressure created by internal leaks in the cylinder across the piston.
In this article, we cover:
How hydraulic drift happens
Several factors can cause hydraulic cylinder drift. Fluid may flow from one side of the piston to the other, creating a pressure imbalance. If the rod seal leaks, the cylinder can become hydraulically locked as pressure around the piston equalizes, resulting in the cylinder drifting toward either the extend or retract position and being unable to hold a load at mid-stroke.
Occasionally, hydraulic cylinder drift is caused by contaminated fluid containing dirt, grit, water, or air, which can damage seals or sealing surfaces. Excessive heat is another common factor: when system temperatures rise, seals endure extra wear, harden prematurely, and become brittle.
To identify the source, a hydraulic cylinder drift test can help pinpoint whether the issue is due to seals, contamination, or pressure imbalances. Always ensure the correct seals are used and that operating conditions remain within the recommended temperature range.
Why does hydraulic drift matter?
Hydraulic drift occurs when hydraulic cylinders fail to maintain their position under load, leading to unexpected movement or gradual slipping. Fluid movements become rough, jerky, and start or stop abruptly. This creates a serious safety hazard, particularly in heavy machinery, construction equipment, or other hydraulic equipment where precision is critical, putting operators, maintenance crews, and surrounding worksite environments at risk.
A common cause of hydraulic drift is internal pressure imbalances, often due to internal leaks, damaged seals, or uneven hydraulic fluid pressure. Over time, this can lead to wear and tear, misalignment, or even catastrophic cylinder failure. Fluid contamination—such as dirt, grit, water, or air—can also damage seals and disrupt proper cylinder operation, making the drift more likely. When drifting occurs, it is a clear sign that the cylinders aren’t performing efficiently or as intended.
Failing to address hydraulic drift results in equipment downtime, operational delays, and expensive repairs, increasing overall maintenance costs. To prevent this, regular inspection, diagnostics, and preventive maintenance are essential. Check for signs like fluid leaks, pressure imbalances, irregular piston movements, and contaminated hydraulic fluid. Use quality hydraulic fluid, maintain proper filtration, and ensure seal integrity to extend the lifespan of your equipment.
Investing in proactive solutions, such as hydraulic monitoring systems and regular cylinder servicing, can mitigate risks and ensure your hydraulic equipment remains reliable, safe, and cost-effective. By staying on top of the situation, you reduce the likelihood of unexpected equipment failure while enhancing performance, productivity, and worksite safety.
Step 1: Understand the physics
This will help you troubleshoot more effectively. Hydraulicspneumatics.com explains the physics behind drift:
If a closed-to-actuator or cylinder spool blocks a double-acting cylinder service port, and the leaking piston seal allows fluid to bypass, pressure will spread out on each side of the cylinder's piston.
Remember, this is the condition needed to achieve hydraulic lock, and drift comes to a standstill—unless fluid can leak from the cylinder or the cylinder's circuit, such as through a leaky valve.
In order to support the same load, the static pressure in the cylinder needs to increase. This is because of pressure acting on the rod-side annulus area due to the loss in effective area.
Example: Say the load-induced pressure on the cylinder's piston side is 2,000 PSI. On the rod side, when the DCV is centered, it's zero. Assuming no leak fluid occurs past the spool and depending on the areas' ratio, the equalized pressure may be 3,000 PSI.
Now, let's say the circuit has a service port relief valve set at 2,500 PSI. The pressure will start to balance itself across the piston seal.
The static pressure on the cylinder's piston side will increase, reaching the cracking pressure of the port relief. When this happens, the cylinder will begin experiencing hydraulic cylinder drift.
Monitoring these conditions can help identify signs of cylinder drift early, such as slow movement, jerky motion, or inability to hold a load at mid-stroke.
Step 2: Troubleshooting
Given the nature of how hydraulic drift occurs, you'll appreciate why a pressure gauge is helpful in diagnosing the cause. You should troubleshoot using pressure testing under controlled conditions.
Piston seal leak
Even if this happens, it's not always the reason for hydraulic drift. If your ports are unblemished and the cylinder is full of hydraulic oil, the cylinder will maintain its load without a hitch. That is, until a leak happens at the rod seal.
Rod seal leak
hen the rod seal is not intact, then expect the negative pressure vacuum on the piston side to dissipate. When that happens, the piston rod will stop working due to pressure equalizing throughout the cylinder.
Pressure gauge readings
When a leak is not obvious, use the pressure gauges on the cylinder. A hydraulic fluid leak reduces the cylinder's effective area. As the pressure increases on the rod side, so, too, must the pressure in the piston side. This will ensure the same load is maintained.
To calculate the equalization pressure, refer to the piston-side pressure before the leak compared to the pressure on the rod side. To better understand this, let's say the rod size pressure is zero PSI. On the piston side, pressure is 2000 PSI. Then equalization will take place at 3000 PSI.
Once you achieve equalization, you stop further drift and hydraulic lock from happening again, until more hydraulic fluid leaks occur. Note, some port relief valves prevent a cylinder from reaching equal pressure. This is due to set lower pressure levels. So in the example we just gave, hydraulic drift will continue as overall pressure hits 2500 PSI.
Note, if the cylinder is drifting: The directional control valve or load control valve could be the problem if, across the piston seal, there is a lack of equalization of pressure.
Preventing hydraulic drift
Your best options to prevent hydraulic cylinder drift are:
Your best options to prevent hydraulic cylinder drift are:
- Always use a quality hydraulic cylinder, especially for critical applications like double rod cylinders, to ensure reliable performance.
- Install quality seals to prevent bypass and leakage, which can occur when fluid pressure equalizes across the piston.
- Undertake regular maintenance of your cylinder. Inspect the rod for corrosion, uneven wear, or damage, which can contribute to causes of hydraulic cylinder drift.
- Keep your hydraulic fluid clean. High-quality breather caps help prevent fluid contamination, moisture, and particles from affecting higher fluid pressure areas when hydraulic fluid enters.
- Service your accessories, including components such as rod eyes, ball joints, or other connections. Neglecting these can lead to misalignment, uneven load distribution, and even equipment failure.
- Check and maintain pressure relief valves, as faulty or incorrectly set valves can allow pressure to equalize across the cylinder, increasing the risk of drift.
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