How to Bleed A Hydraulic Cylinder

A hydraulic cylinder is a device that comprises of the piston and cylinder. The piston actuates because of the pressure of hydraulic fluid within cylinder. This results in transformation of the hydraulic energy to linear movement.

By using this movement of piston you can accomplish different tasks, including pulling, pushing or even lifting. You can find this hydraulic cylinder in loader, bulldozer or power lifts. This way, you can double up convenience and productivity.

Reasons for Bleeding Hydraulic Cylinders

Hydraulic bleeding is extremely important for hydraulic systems to work properly.

Entrapment of Air in Cylinder

The air can get into the hydraulic system during a maintenance operation or when it is open for repairs. Some sponginess or work inefficiency may arise in the cylinders if there are many air bubbles in the hydraulic fluid. The trapped air is expelled by bleeding the cylinders, allowing the hydraulic fluid to run smoothly.

Entrapment of Air in Cylinder
Insufficient hydraulic Fluid Filling

Insufficient hydraulic Fluid Filling

An inadequately filled hydraulic system with air pockets or if air pockets remain after refilling. Following this will cause the wrong cylinder to operate. Furthermore, you must bleed the cylinders to fill the air pockets with the fluid. It prevents the air from affecting the function of the pistons working within the cylinders.

Contaminants in Hydraulic Fluid

Various contaminants including the debris, or dirt impact the smooth functioning of the hydraulic cylinder. This negatively impacts the oil quality and the cylinder. A bleeding hydraulic cylinder helps flush contaminants from the system. Hence keeping the quality of the hydraulic fluid high for ultimate efficiency.

Contaminants in Hydraulic Fluid
Hydraulic System Maintenance

Hydraulic System Maintenance

A key element in the avoidance of things like pressure faults, leakage or depletion of the hydraulic pressure is the proper maintenance. Bleeding allows you to discover and fix the air or fluid problems before they become real problems.

Preparations for Bleeding Hydraulic Cylinders

Safety Precautions

A number of preventive measures you need to act upon. Some of the key ones are:

  1. Make sure you employ or wear proper (PPE) personal protective equipment including safety glasses and gloves. You can ensure protection from debris and hydraulic fluid.
  2. Ensure the equipment is off and de-pressurized before starting any work.
  3. Inspect for any leaks or damaged parts that can cause a threat.
  4. Never place your hand or body near the moving parts of the hydraulic system.
  5. Take care of the hydraulic fluid, which works under high pressure. This might result in irritation or burns in case of skin contact.
Tools and Equipment Needed

You need multiple materials and equipment to begin bleeding the hydraulic cylinder:

  • Socket Set or Wrench
  • Container or Catch basin
  • Towels or Clean rags
  • Hand Pump
  • PPE (Personal protective equipment)
  • Manufacturer’s manual or documentation

Step-by-step Hydraulic Cylinder Bleeding Procedure Process

The following section highlights the key points you need to follow to bleed the hydraulic cylinder:

Step 1: Identify the Bleeding Screw/Valve

You begin by identifying the bleeding screw/valve. The bleed valve is commonly a little screw or plug that resides on the cylinder body. This is to free any trapped air from the system.

Step 2: Position the Cylinder

You must put the hydraulic cylinder in the right position for bleeding. Secure the cylinder in a safe and stable position. While securing the position, ensure the screw/valve faces open air.

Step 3: Bleeding Valve Opening

Through using the socket or a spanner you can open up the bleeding screw/valve. Take care not to reduce it too much. Otherwise, you will end up getting the valve out of its place. Open enough to facilitate easy escaping of air.

Step 4: Allow Air to Escape

Start the hydraulic system by pressuring the cylinder in the open bleed valve state. When the system pressurizes, air previously trapped inside the cylinder will leave through the bleed valve. What you may hear are hissing or bubbling sounds as the air leaves.

Step 5: Bleeding Valve Closing

Let the air out and wait some time until you no longer hear the sound of escaping air. With that done, turn the bleed valve clockwise. See that it is tight but not too tight to avoid thread damage.

Step 6: Testing Hydraulic Cylinder Functionality

The cylinder should be bled, and its functionality should be tested to ensure correct operation after. Turn on the hydraulic system, and the piston will move through its entire range of motion within the cylinder. Listen to any strange sounds, vibrations, or reduced speeds. This may indicate any trapped air or issues with the cylinder and the hydraulic systems.

Step 7: Checking for Leaks

Finally, examine the hydraulic cylinder and other surrounding parts for any oil leaks. Check for hydraulic fluid seepage around fittings, seals, and joints. If you uncover a leak, handle it at once to prevent hydraulic fluid loss and make the system whole again.

Factors That Affect Hydraulic Cylinder Bleeding

Factors that directly influence the hydraulic cylinder bleeding process are.

1. Air Entrapment

Air entrapment affects the smooth functioning of the hydraulic cylinder. The presence of air bubbles may affect aeration and reduce the fluid’s capability to communicate force. You can avoid air entrainments with proper hydraulic system bleeding during installation and maintenance.

2. Fluid Contamination

Contaminants like mud, garbage and water in the hydraulic fluid can cause the bleed process disruption. These pollutants can obstruct valves and passageways, leading to irregular fluid flow. You should check and replace filters to reduce contamination and extend the system’s life.

3. Temperature

Abnormal temperatures will make the hydraulic fluid change its viscosity. This will influence the smoothness of its flow characteristics and bleeding process. In colder temperatures, the fluid may become thicker, weakening the ability to bleed air from the system. In contrast, high temperatures result in fluid expansion and air entrapment. You should monitor and meet the operating temperature range specified for your hydraulic system for the best bleeding result.

4. System Design

The arrangement of the hydraulic system’s components, including the positioning of valves, hoses, and tanks, can affect the bleeding process. A correctly designed system will help to provide proper fluid flow and to eliminate air while bleeding. Ensure elements are properly sized and oriented to prevent air entrapment and facilitate bleeding out.

5. Size of System

Consider the system size as it greatly influences the bleeding phenomenon. Bigger cylinder allow you to incorporate more effort as well as time. Also, the bigger cylinder makes use of more fluid and entraps more air.

6. Type of Fluid

Various properties of the hydraulic fluid affect the bleeding process of the cylinder. The key properties includes the fluid viscosity as well as releasing of air. Make sure to select the fluid featuring complete compatibility with the cylinder components as well as the fluid.

7. System Pressure

The pressure of the system influences the cylinder bleeding. Higher pressure can result in quick bleeding process by pressurizing the air to move out. In contrast the lower pressure negatively influence bleeding. It makes the process difficult and cumbersome. Therefore, you need to keep an eye on the pressure of the cylinder.


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