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RE: Thru hull seals
Gene,
First, some details on seals for rotating shafts.
Hydraulic seals rely on a thin film of oil providing lubrication at the
interface of the seal material and the shaft. In a sub there is air on
one side of the seal and water (with or without salt) on the other. To
use the seals you are talking about requires redundant seals with a
(waterproof) grease zone in between. The inner seal is the pressure
seal and the outer seal is just keeping the grease from being washed
away. A slightly better version is to pressurize the grease zone at
ambient plus a few psi with a spring loaded, pressure balanced,
automatic feed grease cup (fancy description but really quite simple).
In this version the outer seal is reversed as the pressure is higher at
the grease zone than the water. In either case the grease zone can be
used to lubricate the journal bearing surface which supports the shaft.
Now for sliding seals.
These would require an extendable boot which would keep the grease film
from being washed off by the water and they always require some sort of
force balance. The shaft will be pushed into the hull with a force
equal to the cross sectional area times the water pressure (and this
will change with depth). Generally speaking, don't use a sliding shaft
through the hull!
Hope this makes some sense.
> ----------
> From: HUNTR2@aol.com[SMTP:HUNTR2@aol.com]
> Sent: Wednesday, September 09, 1998 8:30 AM
> To: personal_submersibles@psubs.org
> Subject: Re: Thru hull seals
>
> John Brownlee,
> Hi, I see you work at the Lunar and Planetary lab. So they
> discovered
> water on the moon.... I didn't realize there was enough to support a
> submarine mission! lol
>
> On the thru hull seal question.... The hydraulic industry seals
> rotating
> and sliding shafts to 3000 psi all the time... a standard
> specification for
> hydraulic cylinders and motors. Why reinvent the wheel? Question
> to
> general membership... Does anyone have input on reasons NOT to use
> hydraulic
> seals, especially since you can engineer redundant seals in a short
> space on
> one shaft.
>
> Gene
> Manteca Ca.
>