What is swing cylinder?

A swing cylinder, also known as a rotary cylinder or a pneumatic rotary actuator, is a type of pneumatic actuator that converts compressed air energy into rotary motion. Unlike linear cylinders that provide straight-line motion, swing cylinders deliver angular movement. This makes them particularly useful in applications where space constraints prohibit the use of a standard linear cylinder, or where rotational movement is required.

How does swing cylinder work?

Swing cylinders operate based on the following principles:

  1. Air Pressure Application: Compressed air is fed into the cylinder, creating pressure that moves a piston.
  2. Conversion to Rotary Motion: The motion of the piston is converted into rotary motion. This is typically achieved through a rack and pinion mechanism inside the cylinder. The linear motion of the rack (driven by the piston) turns the pinion, which is attached to an output shaft, thus creating rotation.
  3. Controlled Rotation: The degree of rotation (angle) can be controlled by the design of the mechanism, commonly ranging from 90 degrees to 270 degrees or more.

Backhoe swing cylinder removal


Removing a swing cylinder from a backhoe involves a series of steps that must be followed carefully to ensure safety and avoid damage to the machine. The swing cylinder in a backhoe is responsible for allowing the entire backhoe arm (including the boom, stick, and bucket) to swing left or right. Here’s a step-by-step guide to removing a swing cylinder from a backhoe:

Step 1: Prepare the Area and Machine

  • Safety First: Ensure the machine is off, keys removed, and the equipment is on stable ground.
  • Position the Equipment: Position the backhoe’s arm and attachments in a stable and neutral position, ideally with support stands or blocks to prevent movement during the repair.

Step 2: Relieve Hydraulic Pressure

  • Bleed the Pressure: Before disconnecting any hydraulic lines, make sure to relieve the hydraulic pressure to prevent fluid spray or sudden movement of hydraulic components.

Step 3: Disconnect Hydraulic Lines

  • Catch Fluids: Place a basin under the cylinder to catch any leaking hydraulic fluid as you disconnect the lines.
  • Disconnect Lines: Use the appropriate wrench to loosen and disconnect the hydraulic lines from the swing cylinder. Cap the lines and the cylinder ports to prevent contamination.

Step 4: Remove Mounting Pins or Bolts

  • Access the Pins/Bolts: Locate the pins or bolts that secure the swing cylinder to the frame and the swing mechanism.
  • Remove Hardware: Use the appropriate tools to remove the mounting pins or bolts. You might need a hammer and punch to drive out pins if they are tight or corroded.

Step 5: Remove the Cylinder

  • Manual Removal: Depending on the size and position, you may need assistance to support the cylinder as it is detached.
  • Carefully Detach: Gently remove the cylinder from its mount, being careful not to damage any seals or the rod surface.

Step 6: Inspect and Clean

  • Inspect the Cylinder: Once removed, inspect the swing cylinder for any signs of wear, damage, or leaks. Decide if it needs repair or replacement.
  • Clean the Area: Clean any debris and spilled fluids from the work area and the cylinder mount points on the backhoe.

Step 7: Prepare for Reinstallation or Replacement

  • Replace Seals or Cylinder: If you are reinstalling the same cylinder, consider replacing the seals before reinstallation. If replacing the cylinder, ensure the new one matches the specifications of the original.

Swing cylinder repair

Repairing a swing cylinder involves several steps, primarily focused on troubleshooting the issues, disassembling the cylinder, replacing worn or damaged components, and reassembling the unit. Here’s a comprehensive guide to repairing a swing cylinder, commonly found in backhoes and other hydraulic machinery:

Step 1: Diagnose the Problem

  • Identify Symptoms: Common signs of a malfunctioning swing cylinder include leaks, reduced movement efficiency, strange noises during operation, or complete failure to actuate.
  • Inspect Visually: Check for visible signs of wear, damage, or leakage around the seals and cylinder body.

Step 2: Disassemble the Cylinder

  • Relieve Pressure: Ensure all hydraulic pressure is relieved from the system to prevent accidents.
  • Remove the Cylinder: Follow the steps outlined in my previous response for safely removing the swing cylinder from the machine.
  • Disassemble the Unit: Carefully take apart the cylinder. This typically involves removing the end caps, extracting the piston from the cylinder tube, and sliding out the piston rod.

Step 3: Inspect All Components

  • Examine Each Part: Look for signs of wear, scoring, or corrosion on the piston, rod, cylinder bore, seals, and bearings.
  • Measure and Compare: Use calipers or a micrometer to measure the wear on the piston and rod, comparing them against manufacturer specifications.

Step 4: Replace Damaged Parts

  • Order Replacement Parts: Obtain any necessary replacement parts specific to your model. This may include seals, the piston, the rod, or even the entire cylinder barrel.
  • Install New Seals and Gaskets: Always replace the seals and gaskets during a cylinder repair to ensure a tight fit and prevent leaks.

Step 5: Reassemble the Cylinder

  • Clean All Parts: Thoroughly clean all components with appropriate solvents and dry them before reassembly.
  • Assemble the Cylinder: Reverse the disassembly process to put the cylinder back together. Ensure all parts fit smoothly and securely.
  • Lubricate: Apply hydraulic fluid to the seals and the inside of the cylinder barrel to facilitate reassembly and operation.

Step 6: Reinstall the Cylinder

  • Mount the Cylinder Back: Secure the swing cylinder back onto the machine, reconnecting all hydraulic lines and ensuring all fittings are tight.
  • Reconnect Hydraulic Lines: Ensure all hydraulic connections are secure and leak-free.

Step 7: Test the Repaired Cylinder

  • Refill Hydraulic Fluid: Top up the hydraulic system if necessary.
  • Run the Machine: Activate the swing function to test the repaired cylinder. Watch for smooth operation and check for leaks.
  • Adjust as Necessary: If the cylinder does not operate smoothly or leaks, additional adjustments or replacements may be necessary.