[PSUBS-MAILIST] MBT valve

[Alec Smyth]

Hi Jon,

Personally if I used a remotely operated valve I'd be much more comfortable
with actuating it pneumatically than electrically, for reliability. This is
after all the MBT valve, arguably the one thing on the sub that has to be
the most reliable of all. If for some reason it just had to be electric,
then I'd suggest using an electromagnet instead of a motor. The magnet
would act against a spring so that the valve was of the normally closed
type, and you could still surface if the electrons got wet.

What I don't like about the K valves is the way George mounted them. But
I'm a fan of the approach if you add a proper through-hull for the shaft,
sealed with O rings instead of RTV like the original. If using a large bore
valve, I'd add one more detail, which is to put round handles on them
instead of straight ones. That's so that someone getting in or out of the
sub won't dive it by snagging their clothes on the handles.


Best,

Alec


On Sat, Nov 23, 2013 at 11:51 AM, Jon Wallace <jonw at psubs.org> wrote:

>
> 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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