[PSUBS-MAILIST] MBT valve

[Alec Smyth]

One more thing... I'm not sure how easy it would be to get a really
accurate seal if you make the body from PVC. I always find plastics
challenging when it comes to machining tolerances. For surfacing the sub a
tiny valve leak is no problem, in fact you wouldn't even notice it. But a
tiny leak is a nuisance, because the sub will have a tendency to dive
herself in slow motion when you leave her at the dock for a few hours, when
she's under tow, etc.

:)

Alec


On Sat, Nov 23, 2013 at 12:35 PM, hank pronk <hanker_20032000 at yahoo.ca>wrote:

> Jon,
> I have to agree with Alec.  I would not use an electric motor.  If it has
> to be electric, I would also go with solenoid valves.   I have personally
> used solenoid valves on my salvage rov  and in about a million dives we
> never had a single issue except for freezing when the rov surfaced in the
> winter.   Electric solenoids are also safe in your case because you have
> multiple mbt's and you should wire them separately.
> Hank
>
>
>   On Saturday, November 23, 2013 10:10:28 AM, Alec Smyth <
> alecsmyth at gmail.com> wrote:
>  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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