Hi...
The
pressure balance on the system could be a double acting Bimba (they have
SS cylinder that won't rust) with hydraulic fluid on one side and open
to the outside on the other. If the rod comes out on the hydraulic
side then the hydraulic system pressure will always be slightly higher
(the difference in areas between the piston area on one side and the piston
area minus the rod area on the other) in the steering / plane operating
hydraulics than the outside water pressure. The system would be self
compensating as to depth (pressure). You have to compensate both
sides of the system. I have used Bimba's to pressure compensate systems
to pressure as high as 2500 psi in the past. You have to have a large
enough cylinder volume to allow temperature compensation for the system
volume change.
However an actuator can likely be selected
that can be submerged (the seals will work both ways) and then compensation
is unnecessary. They won't be rated for this but will work.
Jay.
ShellyDalg@aol.com Sent by: owner-personal_submersibles@psubs.org
17/02/2007 08:38 AM
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Re: [PSUBS-MAILIST] through-hulls
Joe, Vance, and all. I haven't found the
old catalogue but I'm looking on the net for these things.
As to the pressure and water, the set-up
I saw was not designed for a wet application. Without a pump, the internal
pressure of the system isn't much, and in fact wouldn't be anything until
you turned the wheel to move the rudder. But it IS a closed system. I'm
thinking of two ways to keep the water out.
First, add a small pressurized oil tank to
the system, and with a scuba regulator, keep the pressure in the tank slightly
above the water pressure ( at varying depths/pressures )
As the system is a closed loop, the differential
pressure across the positioner would be the same as if there was no external
pressure ( sea water )
The other idea would be to put the positioner
in a compensated container with the shaft extending through a seal. Again,
you'd need to have a scuba regulator or other air line keeping the pressure
inside the container slightly above ambient.
The positioner is nothing more than a double
acting hydraulic cylinder. They run about $100 or so, and are easy to get,
modify, fix, and replace.
The master cylinder is pretty much the same
thing, but it had a rack-and-pinion set-up on it that moved the piston
back and forth, moving the fluid from one side to the other through the
positioner.
I can't remember what the cost on this thing
was, but it was pretty cheap.
I'll keep looking, and maybe call a couple
of hydraulic equipment suppliers to see if they have any leads.
Frank D.
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