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Jay, I was thinking of making the grooves some what deeper and larger so that if any sand got in the grooves it might still seal properly. Since sand might sit the the grooves I was thinking that reversing the position of the grooves to the land side and installing the gasket onto the piston might better keep the sand flushed out. I was also considering making the soft gasket a bit thicker so it would resist overall deforming better. Perhaps the gasket could be attached in a conical shape to the piston, much like the shape of my current plunger, so the sand couldn't sit on it as easily, then if it was flat. Of course then the grooved surface would need to match that angle. Szybowski From: bottomgun@mindspring.com To: personal_submersibles@psubs.org Subject: RE: [PSUBS-MAILIST] MBT valve Date: Thu, 15 Jan 2009 14:26:36 -0500 Brent, I didn’t reply fully to your previous post. The lands could be fewer/further apart but I wouldn’t make them taller. You want them to be depressed in the low durometer gasket material but you don’t want too much deformation of the gasket as it will speed its deterioration/shorten its life. R/Jay
Respectfully, Jay K. Jeffries Andros Is., Bahamas
As scarce as the truth is, the supply has always been in excess of the demand. -Josh Billings
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of ShellyDalg@aol.com
Hi Brent. Just a random thought......I think the hinged idea may be problematic. If the tolerance is close enough to assure proper alignment, it may be so tight that it can "jam" after a little wear or temperature change. Most poppet valves use a central shaft moving up and down in a sleeve, spring loaded to keep it closed, and a linkage arm that depresses the disk from above. The disk stays in the middle, and the linkage arm and associated mechanism doesn't require any close tolerances. To achieve a smooth exterior surface, you could put the sleeve, shaft, and spring on the inside of the valve, and the linkage arm could pull the disk down from the bottom, rather than push it from above. The disk and seat can be made from plastic, fiberglass, or stainless. It doesn't need to hold any high pressure so it wouldn't need to be that strong. The mounting for the sleeve would need to be stainless, and the shaft also, but very little needs to be "close tolerance" work. The shaft and bushing are "off the shelf" parts. The disk and seat can be machined from plastic ( or stainless ) with a doughnut type gasket set onto the seat.The disk simply pushes up against the rubber gasket with spring pressure. Making the gasket soft and wide ( 1 inch ) would make a little sand not a problem. I don't have the computer skills to draw this so.....Picture your same design, with a shaft attached to the center of the disk. The shaft extends down from the disk center, through a bushing mounted on a "T" shaped piece, that's attached to the underside of the MBT hole. A spring on the shaft pushes the disk up onto the seat. The shaft goes through the bushing and has a linkage "L" on the bottom end that when pulled, opens the valve by pulling the disk down. With the disk being smooth, very little sand can collect on it's surface, and the doughnut gasket points down so no sand will get on it. Any sand or grit that goes in there will simply be washed away by the water as it goes through the valve. The whole valve assembly mounts directly onto the MBT hole with small bolts/gasket so can be removed from above for maintenance/repair. Because I'm not a machinist, I don't approach design with the idea that I can use a machined part. I like to just buy stainless tube and rod that fits together, and weld on whatever else is needed. Like my motor mounts and rudder swivels. I got some 1-1/2 inch stainless bar stock, some stainless tube that fits close, and welded stuff on there to hold the parts, welded some more stuff to bolt it onto the hull, drilled a hole for a grease fitting, and it works fine. The only close tolerance part is the tube and bar stock. If I'm down in Mexico or somewhere and I need a repair, having a mechanism that requires machining could put an end to the dive operation. By using "off the shelf" parts I should be able to repair/replace pretty much any part of the sub right there in the field without having to "make" a complicated piece in a shop. Spare parts and extra stock items like tube, bar, and sheet can be carried along in the truck. A small portable generator/welder and a few basic power tools ( saw, grinder, drill, etc.) and field repairs should be pretty easy. I want to keep this thing as simple as possible, with the ability to fix it where ever I am. Frank D. A Good Credit Score is 700 or Above. See yours in just 2 easy steps! |