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Why didn't I think of that Frank. ;} If you have enough of those flexible tubes hanging out, you can use them as curb feelers, or cat fish whiskers. I'll be watching your progress on the prototype. A couple of things come to mine. When water gets into a hydraulic system and gets churned up to much, the oil becomes milky if I recall correctly. I don't know if that will apply here. The other thing I was thinking about was to just slip one of those types of units inside a hydraulic or pneumatic actuator housing that can with stand the depths your needing it to. Then use the existing rod, ram, and seals that come with the housing. Of course then you would also need a sealed thru hull installed and you may or may not need to oil or air compensate it. Regards, Szybowski From: ShellyDalg@aol.com Date: Thu, 25 Jun 2009 13:00:04 -0400 Subject: Re: [PSUBS-MAILIST] Push Pull Cable Rudder Control Means To: personal_submersibles@psubs.org Hi Alan. The actuator assembly sounds pretty typical. As for the speed of stroke, they are pretty slow for sure. Oil compensating should be fairly easy and definitely needed if more than 15 feet or so of depth is anticipated. My thought on this is......water is heavier than oil, and oil is heavier than air. By making reservoirs part of the envelope, natural separation of the three should be possible using just gravity.
If a small bubble is still inside the actuator, it should eventually work it's way to the upper reservoir. If a little water enters the envelope, it should go to the low spot.
So......if we take the actuator, encase it in a stout fiberglass casing, bond into the casing some threaded PVC female couplings, one on top and one on bottom. Screw into these PVC fittings some hose barb adapters, attach some clear flexible tubing, and plug the ends with threaded PVC fittings and a plug.
This creates the oil reservoirs, above and below the actuator. Now, as the actuator rod extends, a vacuum is created in the FRP casing, and the oil in the reservoirs will fill that space as the flexible tubes compress. The reservoirs would need to be large enough and flexible enough to squeeze whether there was additional outside pressure or not. I'm thinking maybe 1 inch diameter and 6 inches long for each.
With the actuator movement pushing the oil back and forth, any small air bubbles should work their way to the top of the upper reservoir in short order. Like wise, if a small amount of water got in there, it would eventually settle at the bottom of the lower reservoir. Hopefully before it did any damage. With the clear tubing reservoirs, we can see if there's air bubbles or water at a glance, and drain or top off as required.
This was my original thoughts on the Minnkota compensation too. I'm just not sure we need to take these devices apart. Air bubbles will find their way to the top if we give them a path, a little agitation, and time.
Gotta make a method to "top it off" that's easy so maintenance is minimal.
Now, I'll admit, I may be full of S#&* here as I've never actually done it yet, so any criticism is welcome and appreciated. Frank D.
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