Compressor packing and rider bands: materials, wear and when to replace them

Rod packing seals the piston rod where it leaves the compressor cylinder, piston rings seal the piston inside the cylinder, and rider bands carry the piston’s weight so it does not touch the cylinder wall. All three are wear parts. Replacing them on time prevents gas leakage, lost capacity and expensive damage to the rod or cylinder liner.

Rod packing

The packing case sits where the piston rod passes from the cylinder to the distance piece. It contains a series of cups with sealing rings that let the rod slide while holding back the gas pressure.

• Ring types: pressure breaker rings, sealing ring sets (often segmented, for example tangent-cut or radial-cut pairs) and oil wiper rings on the crankcase side
• Materials: filled PTFE for most services; other engineered plastics such as PEEK for higher pressures and temperatures; bronze or cast iron in some designs
• Cooling and lubrication: many packing cases are water- or glycol-cooled and lubricated through the cups
• Vent: leakage that passes the packing goes to a vent that must be routed safely, especially in sour gas

Signs of packing wear

• Rising packing vent flow or vent temperature
• Gas detected in the distance piece or crankcase
• High packing case temperature
• Visible wear or scoring on the piston rod

Piston rings

Piston rings seal the piston against the cylinder bore. As they wear, gas leaks back across the piston, the cylinder heats up and capacity drops.

Signs of piston ring wear

• Loss of capacity
• Higher discharge temperature
• Changes in the PV trace when analyzed

Rider bands

Rider bands (wear bands) support the piston so that it rides on the band, not on the metal. As they wear, the piston drops. If they wear through, the piston touches the cylinder liner and can score it.

How to check rider band wear

Rod drop monitoring measures how far the rod has moved down, which shows rider band wear while the unit runs. Otherwise, measure the clearance at each overhaul and compare with the manufacturer’s limit.

What to send with a replacement request

• Compressor manufacturer, frame model and serial number (nameplate photo)
• Cylinder bore and class, or cylinder serial number
• Rod diameter and the packing case drawing or part number, if you have it
• Gas composition, pressures and temperatures, and whether the cylinder is lubricated or non-lube
• The reason for replacement: routine overhaul or a failure; photos of failed parts help

Send the nameplate photo, rod size and service conditions on the quote form. See also why compressor valves fail.

CHR is an independent supplier and is not an authorized dealer of the manufacturers named.

Frequently asked questions

How often should packing and rings be replaced?

It depends on gas, pressure, speed, lubrication and how clean the gas is. Many operators replace them at planned overhauls or based on condition monitoring, such as packing vent flow and rod drop.

Can I replace only the packing rings and keep the case?

Often yes, if the cups are in good condition and their faces are flat and undamaged. The case should be inspected and lapped if needed at each overhaul.

Are equivalent packing rings as good as OEM?

Qualified equivalents from reputable manufacturers are widely used. What matters is that the material and design suit your service. See OEM genuine vs qualified equivalent parts.