RE: [PSUBS-MAILIST] MBT valve

Brent,

Just a comment on your MBT valve. If you alter the depth of the eat area so that when it is open it has a larger gap it would help. With valves you should have ¼ x diameter lift opening for the same area as the hole.

Yours appears to only have about ¼ inch opening. What is the ratio of vertical gap to diameter in your drawing? It is what we call design review. Hope it helps. Hugh.

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent Hartwig
Sent: 13 January 2009 17:30
To: PSUBSorg
Subject: RE: [PSUBS-MAILIST] MBT valve

Hey Jay,

That assembly looks like it will work well to me, and doesn't look to hard to manufacture, install, or maintain. It's good to see some of your CAD work. It's basically along the lines of what I was thinking of doing when I first started to think about large venting options and from what I was thinking Vances mushroom vents might look like. Having the closure spring inside the pneumatic actuator simplifies things for use both. I like the sealing grooves you used. I had thought at first that the mushroom vents would be partly above the MBT's to let all the air out of the tanks and mount them. But both are assemblies are basically hidden, and yet still let most of the air out. Your blue components, namely the piston and the piston land, I think might be able to be made out of UHMW plastic or the like, or even acrylic for that matter. But I like UHMW for it's ease of machining, much cheaper then SS, it's light so that helps in keeping the weight down (since these are mounted higher up in the subs), and it's very corrosion resistant as far as I'm aware of.

I can see how I could blend your assembly with mine by using your type of upper rubber gasket and grooved plunger/piston, and then just use a SS or UHMW retaining ring to hold the gasket in place basically in the same way you've secured the gasket on yours. The main reason I switched over my thinking from a piston to a hinged plunger assembly was that the top of my MBT's are right next to the knuckle curvature of the steel heads, and my MBT's are not even close to flat on top, unless I modify them.

"Want to mount the complete valve assembly on the tank surface so that if there is give between the hull and the tank surface, closing tolerances and alignment will not be affected."

This point I believe is a good one, and this is why I left as much thickness to my plunger land as I did. I could even add some additional thickness to the underside of the FRP tank shell to beef things up in that area if need be. I can see how that might be good for your assembly as well, not for making it seal better like mine, but primarily for keeping the FRP tank rigid over time. Also I hope to have less trouble with my assembly from any flexing or alignment issues by using a good large soft O-ring(s) or gasket.

Your mentioning having the complete valve assembly on the tanks surface to better deal with alignment issues, gave me an idea of how I could do that with my basic hinge type assembly, and not have to weld the two SS tabs onto the pressure hulls steel heads. I would need to add about a 1/4" of FRP to the bottom of the upper area of the MBT's to beef it up to handle this new configuration. So that means it's back to the salt mines to work up another assembly model. ;)' Thank goodness for soft office chairs.

Regards,
Szybowski

From: bottomgun@mindspring.com
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] MBT valve
Date: Sun, 11 Jan 2009 03:23:15 -0500

Brent & Vance,

Thanks for taking the lead with the illustration of a MBT valve. I have taken the liberty to play with the design some, see the 3 images at http://flickr.com/photos/bottomgun in the MBT Vent Valve group. I believe if you have a FLICKR account, you can view the images at a higher resolution.

Some thoughts:

1. Want to minimize number of moving parts

2. Want to minimize the number of hinge points

3. Want to mount the complete valve assembly on the tank surface so that if there is give between the hull and the tank surface, closing tolerances and alignment will not be affected.

4. Want seating surfaces to mate square on to insure complete closing of valve

5. Seating surface material should be above the valve disk so sand or other matter doesn’t settle on it and allow air to leak

6. Seating material should be a soft elastic material

7. Operating cylinder should fail in the valve closed position (some cylinders have springs installed and air pressure operates against the spring below the piston, not sure if Bimba has this capability)

Bimba cylinders, 3-D models in various formats are available on their web site:

http://www.bimba.com/

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