How To Replace A Worn Or Damaged Piston Compression Ring On Your Oil-Free Air Compressor

Posted on: 1 June 2015


Oil-free air compressors are beneficial in many ways: they are easy to maintain, have reasonable prices, and provide airflow free of lubricants. However, like all air compressors, certain parts will wear out over time and require replacement. One such part that will eventually need replacing in your oil-free compressor is the piston compression ring. If you are experiencing an unexplained loss-of-air from your compressor, a likely cause of the leak is a bad compression ring. Below is how you can replace the ring and get your compressor back up to speed in a short amount of time:

Replacing your piston compression ring - tools and materials needed

  • Replacement piston compression ring for your particular compressor model
  • Socket set with ratchet and appropriately-sized sockets
  • Screwdrivers – both flat blade and Philips head
  • Adjustable wrench
  • Hex key set
  • Mineral spirits
  • Rag or cloth
  • Utility knife
  • Masking tape

Replacing your piston compression ring – step-by-step procedure

1. Unplug the compressor and release all pressurized air – never attempt work on a pressurized air compressor, and be sure that the source of power for the compressor is disconnected. Wrap the plug with masking tape a few times so that others know the compressor is out-of-service.

2. Disconnect the air line from the cylinder head - – the cylinder head on your air compressor will extend away from the compressor housing and is usually covered with vanes that help dissipate heat. Detach the outgoing air line from the cylinder head using an adjustable wrench, and be careful not to kink the air line when moving it out of the way.

3. Remove the cylinder head- several bolts, most likely four, are used to attach the cylinder head; remove these bolts with your socket set and set them aside. Lift the cylinder head straight up from the compressor and set it aside.

4. Remove the reed plate – the next component beneath the cylinder head is the reed. The reed is attached to a special housing plate, and it consists of two or more flexible metal blades. These blades flex up and down with each stroke of the piston; their design permits air to flow out of the cylinder on the up-stroke but prevents air from re-entering the cylinder on the down-stroke. In most situations, the reed and its plate will be attached with the same bolts that you removed in step 2, so it should just lift away from the compressor. However, if your model uses additional bolts to mount the reed plate, take them out so you can remove the plate.

5. Detach the piston from the compressor – after removing the reed and plate, you need to remove the piston so you can access the ring. The piston will be attached with a bolt or screw to the connecting rod which, in turn, is attached to the motor. After removing the fastener, lift the piston up and out of the now-exposed cylinder.

6. Inspect the piston compression ring – the piston compression ring inside of an oil-free compressor is usually constructed of PTFE (e.g., Teflon) or a similar material. Carefully inspect the piston compression ring for signs of tearing, abrasions, thinning or pitting. If you see any flaws, then it is due for replacement. A damaged or worn ring permits air to leak past it on every stroke of the piston.

7. Replace the piston compression ring – after determining the ring needs replacing, use a utility knife to cut it away from the piston. Clean the piston surface with mineral spirits to remove any contaminants and allow it to dry completely. Next, install the new piston ring by sliding it over the piston until it is firmly seated in the ring groove.

8. Reinsert the piston into the cylinder – once the new compression ring is in place, slide the piston into the cylinder. If there are any contaminants inside the cylinder, wipe them away with a cloth soaked in mineral spirits before installing the piston. Check the fit of the piston inside the cylinder to ensure it moves up and down; some resistance is normal, but it shouldn't bind on the walls of the cylinder.

9. Reassemble the compressor parts – working backwards from step 4, reassemble the piston and connecting rod, reed plate, cylinder head, and air line.

If you need more information about repairing your air compressor and other industrial equipment pieces, you can check out sites like