How to Choose the Right Oil Seal for Rotating Shaft Applications
Matching seal lip design and material to shaft speed, temperature and media.
An oil seal keeps lubricant in and contamination out where a shaft passes through a housing. The wrong seal leaks, wears the shaft or burns out quickly, so it pays to match the seal to the job.
Start with the dimensions
Seals are specified by shaft diameter, housing bore and width, in that order: for example 40 x 62 x 8. Measure the shaft where the lip runs, and the bore of the housing. Check the shaft for wear grooves, because a new lip on a grooved shaft will leak.
Choose the lip material for temperature and media
Nitrile rubber (NBR) is the usual choice for mineral oils and greases at moderate temperatures. Fluoroelastomer (FKM, often called Viton) tolerates higher temperature and more aggressive fluids. Silicone handles wide temperature ranges but is not suited to heavy dynamic wear in oil. Check the maker's temperature range against your application, as each compound has its own limit.
Single lip or double lip
A single-lip seal retains the lubricant. A double-lip seal has a second lip, called a dust lip, to keep out dust, mud and water. Use double-lip designs in dirty or wet surroundings.
Metal case or rubber-covered
Seals come with an all-rubber outside, a metal case, or a metal case with rubber coating. Rubber-covered outsides seal better in rough or slightly damaged housing bores.
Speed and pressure
Surface speed at the shaft is a key limit; each lip material has a maximum. Standard seals are made for little or no pressure. If the housing builds pressure, fit a breather or use a seal designed for pressure.
Fitting
Lightly oil the lip, press the seal in square with a tool that bears on the outer edge, and protect the lip from sharp keyways and shaft edges while sliding over them.
Key Takeaways
- Give shaft diameter, bore and width.
- Pick the lip material for temperature and fluid.
- Use a dust lip in dirty or wet places.
- Check the shaft surface before fitting a new seal.
This article is general guidance. For a recommendation for your own application, contact our engineering team. Oil seals and sealing solutions →