Re: [PSUBS-MAILIST] Oil vs air

[VBra676539@aol.com]

In a message dated 2/26/00 4:44:27 AM, paul_suds@hotmail.com writes:

<< On my DPV, I used a high quality rotary seal. Does anyone use an oil 
filled 
motor housings on any of their shallow subs or ROV's? I know this question 
has come up before, and I've always advocated air with a good rotary seal, 
but I've been doing some research on Navy rotary seals and the like. It 
seems that the really deep ROV's and some subs use high dialectric oil with 
pressure compensated diaphragms. My motors are going to be kind of 
expensive,high current, and high voltage. Oil is starting to look 
desirable...Suds >>

I haven't used oil filled motors in years and am not sure I could persuade 
myself to do so again. They aren't complicated, just messy. If you look at 
Phil Nuytton's web page and click to Aquarius, you'll see one of the old Hyco 
5 horse/planetary gear reduced units mounted for lateral thrust just under 
the main viewport. There is another one astern that pivots hydraulically for 
steering (and that was the only one we had when I ran the boat). Leo and PV 
(all the Ps as a matter of fact) used the same thrusters mounted port & 
starboard on a common pivoting shaft, and the same 5 hp motors to drive the 
hydraulics system.

The tail section of the thruster is a sand casting with integral kort nozzle 
and the cable runs through the side flange (and then through a cutter which 
could be operated from inside with a hand pump to shear the thing off in case 
it became entangled). The nose you see on the can is a fiberglas cap. 
Underneath is a "top hat" which is, in fact, the end bladder off a 
tractor-trailer air brake system and serves as the compensation bellows. A 
fitting on the bottom (with the thruster horizontal) and a check valve on top 
served to fill/drain/vent--which has to be done after every dive as the 
things always burp a little oil somehow or other. The thrusters banged out 
about 175 pounds of thrust as I recall, and were about as rugged as anything 
else we used, meaning you could go for weeks without touching them and then 
have to rebuild one every day for another week. As usual.

I don't know why you'd want to compensate the system if you can avoid it. And 
as I recall, you are designing shallow. Most any old pump seal will hold 
that, and if it worries you, put two on the shaft with a bearing between them 
and the inner one running in a compensated oil bath. Perry did that with 
reasonable success--all the way to 3000 feet!

Vance