[PSUBS-MAILIST] MBT valve

[Jon Wallace]

Looking for feedback on this MBT poppet design (see attachment).  It is 
very similar to the poppet Vance showed us in Islamorada but driven by 
an independent electric motor rather than pneumatic.  My goal is to move 
to an electric or pneumatic replacement for the Kittredge MBT ball valve 
thru-hull design for various reasons. First, I don't like the valve 
handles sticking in through the conning tower; second, I am adding 
saddle tanks for additional buoyancy which would mean adding at least 
one more valve; third, my saddle tanks are going to be big and I want a 
large diameter valve to provide quick venting.

Illustration.
The valve is made out of PVC plumbing material available at any good 
hardware store.  The square main body is a 4-inch PVC coupling.  A 
series of 1-inch holes drilled into the end allow venting when the 
"plunger" is retracted back to the motor side.  The "stop" on the closed 
side would have a gasket to provide an air-tight seal.

The motor is a cheap electric screwdriver motor such as Black & Decker 
AS6NG.  It has plenty of torque, reversible, and is low power (2-3vdc).  
When the body is removed the "guts" fit nicely into 1.5 inch PVC 
piping.  The rotating socket tip will be waterproofed using a home-made 
"Blue-Globe" type attachment.  Oil compensation will ensure the housing 
doesn't fracture at depth although theoretically 1.5 inch PVC is 
pressure safe to well beyond the depths I will be diving.

The piston will be 1/4 inch thick (6mm) and can be aluminum or even 1/4 
to 3/8 acrylic.  It is attached to the coupling nut by a 1/4-20 threaded 
rod.  The coupling nut is permanently attached to the rotating socket 
tip of the screwdriver by either epoxy or light welding.  As the motor 
and coupling nut turns, the threaded rod is drawn into the coupling nut 
pulling the piston toward the motor and allowing the MBT to vent.  
Reverse the motor and the piston is forced back down to the closed 
position and seals the MBT.

I have already prototyped the motor and it's PVC housing and they fit 
together very well.  Cost of battery operated screwdriver is about 
$10-20 (US).  PVC of course, is cheap.  I am looking at 4-inch material 
but this design could be easily scaled.

I see lots of pros; looking for cons and potential issues with the 
design before I fully prototype it.  Any of you CAD'rs interested in 
creating a nice 3-D drawing for me?

Jon



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