olam
Member
So why would you use single lip seals when you could fit a double lip of the same width?
What lubricates the outer seal?
What lubricates the outer seal?
lip seals
- Thread starter olam
- Start date
superheat6k
Well-known member
What is the application ?
pvb
Well-known member
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.
VicS
Well-known member
+1 and the space between the seal lips should be filled with grease.
olam
Member
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.
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.
RichardS
N/A
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
superheat6k
Well-known member
For this application that has worked for 20 years I would suggest keeping the arrangement, including seal type, exactly the same.
James_Calvert
Well-known member
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...
rogerthebodger
Well-known member
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?466537-Waterproof-Wheel-bearings-rear-seal
Various types of lip seals
Poignard
Well-known member
All you ever wanted to know about lip seals!
Thanks Roger. :encouragement:
Thanks Roger. :encouragement:
pvb
Well-known member
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.
Laysula
Well-known member
Remember when replacing the seals to specify stainless steel springs.
olam
Member
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.
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.
RichardS
N/A
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
rogerthebodger
Well-known member
Yes I have but many many years ago used when separating two liquids with limited space.
The problem is that if one of the seals gets damaged the liquids could mix giving problems.
If space was not limited I would use two seperate seals with a drain hole between the seals so if one failed there would be no mixing of liquids.
Two seperate seals with drain is how most jabsco engine raw water pumps are designed but there could be some with a double lip as I posted.
I will have a look in my jabsco design manual when I get home
The problem is that if one of the seals gets damaged the liquids could mix giving problems.
If space was not limited I would use two seperate seals with a drain hole between the seals so if one failed there would be no mixing of liquids.
Two seperate seals with drain is how most jabsco engine raw water pumps are designed but there could be some with a double lip as I posted.
I will have a look in my jabsco design manual when I get home