Replacing Hydraulic Cylinder Seals Is Easier with the Right Tools
Here’s a quick guide to changing seals in hydraulic cylinders.
Getting Started: Removing Old Seals
Hydraulic cylinder seals are located in both the piston and the end cap (seal housing).
Seal Housing
On the outside, you’ll usually find an O-ring, which prevents oil from leaking between the housing and the cylinder barrel.
On the inside, there’s a rod seal to stop oil from escaping along the pressurized side of the rod, as well as guide strips that prevent the rod from hitting the housing.
At the outer edge of the housing is a wiper, designed to keep dirt from entering the cylinder with the rod.
Piston
On the inner side of the piston, there is typically an O-ring positioned between the piston and the rod. On the outer surface, piston seals come in a variety of forms, but they can generally be divided into two main types: rubber/plastic seals and Teflon seals. The key difference is that Teflon seals are better suited for higher-speed movement.
The purpose of piston guide rings is to keep the piston properly aligned and supported, preventing contact with the cylinder wall at any point during operation.
When removing seals, use a rounded seal removal tool to avoid damaging the seal grooves—especially on the piston. Scratches or nicks in the groove can become future leak points. After removal, it’s important to thoroughly clean all components to prevent loose debris from entering the cylinder.
Installing New Seals
Start by confirming that the new seals match the ones being replaced
Seal Housing
Install the O-rings into the seal housing using a rounded wrench to avoid damaging the grooves.
When fitting the rod seal, pay attention to its orientation. Many seals have pressure-side lips that are designed to press against the rod under oil pressure, improving the seal.
The scraper (or wiper) that fits into the guide should be tapped into place carefully, making sure it seats evenly around the edge and doesn’t sit unevenly on one side.
The guide usually also includes support rings to reinforce the O-ring—these should be installed last.
Piston
The piston seal is installed by stretching it over the support ring grooves. Use a seal cone or a rounded tool to avoid leaving marks during installation. If you’re working with a Teflon seal, it often needs to be stretched to the correct size before it can be fitted properly.
After stretching, the Teflon seal should be installed quickly to prevent it from shrinking back. Once in place, it’s compressed to its final dimensions using a seal band and reduction sleeve. This prevents the Teflon seal from cracking during installation when the piston is inserted into the cylinder bore.
Lastly, install the piston support rings.
