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There are two options with the double seal. If you are
using just bellows equalizing then the inboard seal is best to be mechanical
and the outboard seal just a Vee seal. This is a minimum length solution. The 2nd option is to have two mechanical seals back
to back with oil between. The oil pressure should be positive above the
sea pressure by about 10-15 psi. Check www.DOERmarine.com
under products – hydraulics-DOER compensator. They have about 1
gallon reservoir that they use for this and other purposes that has a spring
assist to provide the 10-15 psi above ambient. As Vance says you can then
monitor the 10-15 psi and if there is a leak then the pressure drops off but then
the inner seal should hold til you repair the leak. Caution on using
two mechanical seals without positive pressure and also the type of seal as to
which way the pressure should and could act. Hugh From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Smyth, Alec Dang Vance, with I'd pinged you about that beforehand. I did in
fact tap the shaft tunnel for a small pressure monitoring line just as you
suggest, but hadn't put in an inboard seal for the simple reason I knew it
couldn't run dry, yet didn't have the elementary idea of filling the whole
thing with oil! The inboard bearing seat is machined close enough that
there should still be a pressure change to detect, but it would be much better
to have this oil-filled arrangement you describe. I'll take a look at it and
see if I can come up with a way to add that inboard seal, it should be feasible
and I like the idea. thanks, Alec
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of vbra676539@aol.com One more thing. The void space between seals
will need to be oil filled so that the inner seal has something to run in. If
that one leaks, you'll know it pretty quick. What about doing the right thing up front and
installing two seals in line with support bearings in the housing? Then this
entire thread goes away. Install a fitting between the seals and run a small
pressure gauge on a 1/8" hard tube to wherever you want it. If the outer
seal fails you'll see the flooding internally. Then you don't have the issue of
dinging a prop and knocking your shaft minutely out of line which would jam the
works. I've put about a zillion hours on a shaft seal package like that and
never had the first moment's trouble. Hey all.i thought of an idea for sealing a leaking through hull.What about machining a very fine taper onto the outside of the shaft. Then threading the inside of the shaft after it exits the through hull and fitting a wing nut and spacer? Then if the seals leak, you could screw down the wing nut which would pull the taper into the gap and jam it shut?What do you think? Would pressure push the taper in anyway under normal conditions? im thinking of doing this for the drop lead controlls, variable controll and rudder. RegardsJames----- Original Message -----From: Smyth, Alec [mailto:Alec.Smyth@compuware.com]To: personal_submersibles@psubs.orgSent: Mon, 25 May 2009 21:30:02 -0400Subject: RE: [PSUBS-MAILIST] Precision prop shaftThere shouldn't be friction, the shaft rotates freely. I do however plan to leave it out in the sun on the driveway when we get some good hot days, just in case hot temperatures are an issue. Though in the water that would be rather unlikely.________________________________From: owner-personal_submersibles@psubs.org on behalf of Jon WallaceSent: Mon 5/25/2009 8:42 PMTo: personal_submersibles@psubs.orgSubject: Re: [PSUBS-MAILIST] Precision prop shaftNice job Alec. One question I have given the close tolerances. Iwonder if friction caused by rotation of the shaft will cause expansionof the shaft such that it binds or locks up. Any thoughts on this?Jon************************************************************************************************************************************************************************************************************************The personal submersibles mailing list complies with the US FederalCAN-SPAM Act of 2003. Your email address appears in our databasebecause either you, or someone you know, requested you receive messagesfrom our organization.If you want to be removed from this mailing list simply click on thelink below or send a blank email message to: removeme-personal_submersibles@psubs.orgRemoval of your email address from this mailing list occurs by anautomated process and should be complete within five minutes ofour server receiving your request.PSUBS.ORGPO Box 53Weare, NH 03281603-529-1100************************************************************************************************************************************************************************************************************************
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