Bleeding a hydraulic cylinder—how do you do it?

Have you ever noticed that a hydraulic cylinder isn’t working properly? You press the control, but it offers no resistance and doesn’t lift the load, or it only starts working after a few movements? This is a very common symptom that occurs when the system is air-locked. An air-locked hydraulic cylinder often turns out to be practically useless, but the situation is not hopeless. Find out how you can effectively bleed it to restore proper operation of the entire system.

How can you tell if a hydraulic cylinder is air-locked?

The hydraulic system is a key component of many machines and lifting mechanisms. However, the presence of air in the lines causes the entire system to malfunction. Symptoms that most often indicate an air-locked cylinder:

• disturbing and unnatural noises coming from the system,
• jerky operation of the cylinder,
• lack of response to controls, delayed operation.

Air in the system causes the cylinder to lose power, have limited travel, and operate unpredictably. Before you begin bleeding the system, thoroughly inspect its condition and ensure that:

• there are no leaks or fluid loss,
• the lines are intact and undamaged,
• the seals and connecting elements are in good condition,
• the bleed valve is properly tightened.

If you discover leaks or damage, bleeding alone will not solve the problem—air will re-enter the system. In such a situation, repair or replacement of the damaged component is necessary.

How to bleed a single-acting hydraulic cylinder

It is advisable to bleed a single-acting hydraulic cylinder not only when problems arise, but also when installing a new system. When filling the system with fluid for the first time, air always enters the lines, preventing proper operation.

To bleed the system, prepare:

• fresh hydraulic oil or another recommended fluid,
• a container for the leaking fluid,
• tools needed to unscrew the bleed valve,
• a cleaning cloth to remove dirt.

The bleeding process consists of four simple steps:

• Locate the bleed valve.
• Unscrew the valve and wait for air to start escaping. Continue until only fluid is flowing out.
• If foam appears or the fluid mixes with air, top off the fluid level in the reservoir and repeat the process.
• Check if the cylinder is working properly. If not, repeat the steps again.

Bleeding a double-acting hydraulic cylinder

A double-acting hydraulic cylinder is bled in a similar way to a single-acting one, but in this case, the air is released through a hydraulic line located near the pump. Step-by-step procedure:

1. Prepare the appropriate tools to unscrew the hydraulic hose.
2. Extend the cylinder as far as possible. If the movement stops, this indicates the presence of air. Now slightly loosen the hose near the pump and wait for the air to escape from the system. When fluid begins to flow, tighten the hose securely.
3. Top off the hydraulic fluid. Repeat the process until the cylinder operates smoothly.

Checking the oil level in the hydraulic system

Regularly checking the oil level in the hydraulic system is a key part of maintenance. The correct amount of oil not only ensures the equipment operates smoothly but also protects system components from excessive wear.

To check the oil level:

• open the oil reservoir and check the level,
• if it is below the normal level, top off with the appropriate amount of fluid,
• in systems with an oil gauge, read the level on the gauge,
• if there is no gauge, check the manufacturer’s recommendations in the user manual.

Regular oil level checks, bleeding, and maintenance affect not only the machine’s performance but also its operational safety. Minor oversights can lead to a complete system failure.

However, if your own efforts are unsuccessful, it is advisable to contact an experienced service provider. Professional support helps avoid costly downtime and further failures. We recommend the proven hydraulic cylinders and service offerings available at Mechanizacja.