Oil Seal Applications

Good afternoon, I'm after some advice about how to select the appropriate type of oil seal (lip seal) for my application.

I can find plenty on what's available, but nothing on why to choose one type over another.

My application is to replace the shaft seal on a hydraulic gear motor, nothing special, it's an 18 mm shaft in a 30 mm seat, seal length 7 mm. Load's of 'em on the net. Working pressure probably 100 - 200 psi, as the oil its contains is at return (tank port) pressure. Shaft rotation is reversible and typically 2000 rpm.

What are the rights and wrongs of a single lip seal against a double lip seal, and why. The original wasn't spring energised, I guess the oil pressure against the seal energises it, but what little I can find on the 'net says that seals for use with oil would normally have a spring. I have no idea if the one I took out (double lip, no spring) is the appropriate choice, but it has lasted years so it must have had something in its favour.

Thanks, as always, in anticipation of some help.

Best rgds Simon

A lip seal relies on pressure to keep it on the shaft. Pressure can be supplied by a spring or internal oil pressure. Double lip seals are to keep oil in and dirt out. We used to fit two single lip seals with one on the inside the lip is on the outside and the other is fitted in reverse to keep dirty out. The problem with this is lubricating the outer lip. Too high a spring pressure can wear a soft shaft, we used to induction harden in the seal area. If you look at the Trelleborg web site you can find a lot of seal information. It can be daunting selecting a seal as there are many designs which will work in the same environment. As you say the seal you have lasted many years then so long as the shaft is ok repeat.

If the shaft is worn, you used to be able to buy thin stainless steel sleeves to press over the shaft to provide a new running surface, called Speedysleeves.

When fitting the new seal, wrap the shaft with masking tape, or insulation tape so that the lip of the new seal is not damaged by any burrs, keyways or splines on the shaft.

Wet the shaft with oil before fitting the new seal, so that it does not start up dry.

Do not touch the lip of the seal!

The new seal should not run on the same point as the original, it should be sited at least 2 mm from there, so that the new lip"beds " to the shaft.

HTH

Howard