lip seals - YBW Forum

As I understand it, the outer lip of a double lip seal doesn't actually bear on the shaft - the inner diameter of the hole is fractionally larger than the shaft. The outer lip is intended primarily as a protection against ingress of dirt, etc.

+1 and the space between the seal lips should be filled with grease.

+1 and the space between the seal lips should be filled with grease.

The double lip seals I've used are not really two separate lips but only have one spring which squeezes a wider, flatter area than a normal seal onto the shaft. The flat area is slightly raised at each side but there's not really any space that can be filled with grease, unlike using two single seals side-by-side.

From my observation by eye, I would say that both of the raised lips do contact the shaft although the lip closer to the spring will grip more tightly. I suspect that the outer lip is lubricated by the slight by-pass from the inner lip as seals are never 100% effective and there is always some leakage promoted by the rotation.

Richard

Application is a propshaft oil fed seal.Original seals now 20 years old and not leaking
but i want to replace whist boat is on the hard.
3 X seals,1 x forward keeping the oil in ,1 x aft keeping oil in and second one aft keeping water out.

For this application that has worked for 20 years I would suggest keeping the arrangement, including seal type, exactly the same.

Application is a propshaft oil fed seal.Original seals now 20 years old and not leaking
but i want to replace whist boat is on the hard.
3 X seals,1 x forward keeping the oil in ,1 x aft keeping oil in and second one aft keeping water out.

I have an identical arrangement. Be aware that the existing lip seals may have grooved the propshaft and you may want to replace that as well, if you can't adjust things so the new ones bear on unworn sections.

In answer to your original question, I suppose one difference would be that a new double lip seal would in time cut a double groove...

So why would you use single lip seals when you could fit a double lip of the same width?
What lubricates the outer seal?

Depends on what you mean as "double " lip seal

This type is a single lip with dust protection lip. and only seals from one side. The side the spring is





This is a true double lip seal that seals from both sides and has double springs



http://www.ybw.com/forums/showthread.php?-Waterproof-Wheel-bearings-rear-seal

Various types of lip seals

I have an identical arrangement. Be aware that the existing lip seals may have grooved the propshaft and you may want to replace that as well, if you can't adjust things so the new ones bear on unworn sections.

The OP's description sounds very much like a Halyard seal. If it is a Halyard seal, the lips bear on a stainless sleeve around the propshaft, and it should be possible to reposition the sleeve slightly if there's grooving. Thank you all.
Particularly Roger for that info.
Agree i will prob replace like for like but with Viton/Stainless springs.

Replacing shaft at the same time.
Not a Halyard seal.Its a bronze body which i think was originally made by Sleipner the bow thruster people.

This is a true double lip seal that seals from both sides and has double springs

Now that's what I would call a real double lip seal .... although I notice that it is actually called a double spring seal which makes sense.

It raises two questions in my mind

a) has anyone on here actually ever seen a double spring seal? I freely admit to having never seen such a beast in the wild.

b) the usual advice is that the spring side of the seal should face towards the liquid being contained. Obviously this advice is rather redundant in this case unless the seal is being used to separate two liquids .... which raises the thought that perhaps separating two liquids is its raison d'etre?

Richard