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Re: [PSUBS-MAILIST] Precision prop shaft

Oooohhh!!! That's a big one. Those are for big reservoirs (relatively speaking) in active systems. We did NOT have overpressure on our shaft seals, just as a point of interest. The inner seal remains at zero pressure relative and skies up with seapressure when and if the outer seal fails. We used those high priced 16-spring Cranes and I never ever ever saw one fail. It's a heck of a seal.
Vance



-----Original Message-----
From: Hugh Fulton <hc.fulton@gmail.com>
To: personal_submersibles@psubs.org
Sent: Mon, 1 Jun 2009 12:58 am
Subject: RE: [PSUBS-MAILIST] Precision prop shaft

Ther e 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
Sent: 01 June 2009 11:40
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Precision prop shaft
 
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,< /div>
 
Alec
 

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From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of vbra676539@aol.com
Sent: Sunday, May 31, 2009 06:36
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Precision prop shaft
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.
Vance


-----Original Message-----
From: vbra676539@aol.com
To: personal_submersibles@psubs.org
Sent: Sun, 31 May 2009 6:25 am
Subject: Re: [PSUBS-MAILIST] Precision prop shaft
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.
Vance


-----Original Message-----
From: James Frankland <james@guernseysubmarine.com>
To: personal_submersibles@psubs.org
Sent: Tue, 26 May 2009 6:48 am
Subject: RE: [PSUBS-MAILIST] Precision prop shaft
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.  
 
Regards
James
 
----- Original Message -----
From: Smyth, Alec [mailto:Alec.Smyth@compuware.com]
To: personal_submersibles@psubs.org
Sent: Mon, 25 May 2009 21:30:02 -0400
Subject: RE: [PSUBS-MAILIST] Precision prop shaft
 
There 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 Wallace
Sent: Mon 5/25/2009 8:42 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Precision prop shaft
 
 
 
 
Nice job Alec.  One question I have given the close tolerances.  I
wonder if friction caused by rotation of the shaft will cause expansion
of the shaft such that it binds or locks up.  Any thoughts on this?
 
Jon
 
 
 
 
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