Oil seals and rotary shaft seals: a selection guide

When a rotating shaft exits a housing filled with oil or grease, a component is needed to keep the lubricant inside and stop dirt getting in. That is the job of the oil seal, also called a radial shaft seal. It is found in motors, gearboxes, pumps, compressors, wheel hubs, PTOs and countless other applications.

How an oil seal is made

A standard oil seal consists of:

• a metal case, which gives rigidity and allows it to be fixed in the housing;
• a sealing lip in elastomer, which rests on the shaft;
• a garter spring that keeps the lip in contact with the shaft despite wear and temperature changes;
• in many versions, a secondary dust lip facing outwards.

The most common types

• Rubber-covered outer surface: the case is coated with elastomer; it adapts better to rougher housings or light-alloy housings and provides good static sealing on the outer diameter.
• Metal outer surface: provides a very precise and stable fit in the housing.
• With or without dust lip: the dust lip is recommended in dusty or wet environments.
• Pressure versions: with a reinforced lip for applications where the lubricant is under slight pressure.
• PTFE or composite rotary shaft seals: for high speeds, high temperatures or special fluids.

In our catalogue you will find several families of oil seals and shaft seals, as well as rotary seals for hydraulic applications and V-rings as an additional axial seal.

How to measure

An oil seal is identified by three dimensions, usually written as d x D x b.

1. d – shaft diameter;
2. D – housing diameter (outer diameter of the seal);
3. b – width (thickness) of the seal.

For example, 35 x 52 x 7 means an oil seal for a 35 mm shaft, a 52 mm housing and a width of 7 mm. Measure the shaft in an unworn area and, if possible, measure the housing directly rather than the old seal.

Choosing the material

• NBR: the standard choice for mineral oils and greases at medium temperatures.
• FKM: for higher temperatures, high surface speeds and synthetic or additive-rich oils.
• Other materials: for special conditions (aggressive fluids, extreme temperatures).

The shaft matters as much as the seal

The sealing lip runs on the shaft: if the surface is scratched, corroded or has a groove worn by the old seal, the new one will leak too. In these cases you can shift the lip's running position slightly (if the housing allows) or restore the shaft surface. Shaft eccentricity and vibration also affect seal life.

Correct installation

1. Clean housing and shaft; remove burrs and sharp edges.
2. Lubricate the lip with the same lubricant as the application: a seal that starts dry is damaged within minutes.
3. Respect the direction: the main lip with the spring faces the lubricant to be retained.
4. Use a driver or tool that pushes evenly around the whole circumference, never direct hammer blows.
5. Protect the lip from keyways and threads when sliding it onto the shaft.

With the search by dimensions you can enter shaft diameter, outer diameter and width and immediately find the available oil seals. For special applications (high speeds, pressure, special fluids) our technical support will help you identify the most suitable solution.

Frequently asked questions

Can I fit two oil seals one behind the other?

In some applications yes, for example in very dirty environments, provided there is space and the second seal is lubricated. Alternatively, a V-ring can be added as external protection.

Why does a new oil seal leak straight away?

The most frequent causes are a grooved or scratched shaft, dry assembly, wrong direction or a lip damaged during fitting.

Are there oil seals for inch shafts?

Yes, inch series exist. Measure the shaft and housing accurately and give the dimensions in the search or in your support request.