Re: [PSUBS-MAILIST] Pressure compensation

["Paul Suds" <paul_suds@hotmail.com>]

I've done some experimenting with both balanced rotary seals used on 
submarines (USN) and oil compensated housings. I used pressurized air on 
water as the outside pressure source, with both rotary seals and a simple 
diaphragm bladder on the casing for compensation. Both worked very well 
individually and combined. I originally had a problem with a rotary balanced 
seal, but I learned that it needed to be run wet for a while before 
subjecting it to pressure. I would like to use both, but the oil filled case 
cut my power by about 10 percent. I used transformer oil from a large 
transformer that has an extremely high dialectric constant and low 
flammability. This may have been an overkill. I would say a good rotary 
balanced seal is fine without the case being filled and balanced. I will 
probably use both because I tend to overdesign. I would certainly adequately 
cool the case if it is oil filled though. Mine got pretty hot. Haven't done 
the heat loading calcs yet, but this will be another experiment.
The big problem with magnetic drives is the loss of efficiency (flux loss). 
I looked at machining differnt housings, but after reading much material, 
didn't even pursue it, although reliability is 100%, for those that are 
willing to give up performance.
Suds
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