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Design help for propane valve

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Design help for propane valve

Unread postAuthor: Futterama » Thu Feb 18, 2016 8:22 am

Hi forum,

I need to build a propane valve that can be actuated by an RC servo. This means that the range of travel of the controlling surface is limited and the force needed to open and close the valve should be low.

Due to the travel limitation, I cannot use a screw type valve (see attached drawing) where it's just a brass needle pressing onto a hole when closed.
With a low travel distance, e.g. 5mm/0.2", the torque from the servo would be higher than with a longer travel distance. The force the servo can press or pull at 5mm/0.2" distance would be something like 5-10kg/11-22lbs.

Propane pressure would be no more than 6bar/87psi.

I'm thinking that it should be a valve type where the pressure from the propane would close the valve so the pressure would help seal the valve. But then this might also prevent the servo from opening the valve due to the limited force of the servo.

I have been thinking about a design as attachment number 2, simply a pin that goes into an O-ring and seals off the propane flow. Would this work? Or would the O-ring be a weak link? What would happen if liquid propane would enter by accident, would it block up the movement of the pin into the O-ring? I would of course have something that keeps the pin from shooting out to the right.

Another idea comes to mind. I will be using the type of propane canister with a built-in valve (Lindal B188 valve), it's those EN 417 threaded canisters. That valve needs to be pressed down for the propane to flow, and is pressed when you attach your device to the canister. But maybe I could make the servo push that valve pin down and open up the flow that way.

Please add your comments to this :)
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Re: Design help for propane valve

Unread postAuthor: jrrdw » Thu Feb 18, 2016 8:46 am

Fuel valve from a propane fueled forklift would work better or a electric solenoid similar to that would be better IMO.
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Re: Design help for propane valve

Unread postAuthor: jimmy101 » Sun Jun 26, 2016 3:25 pm

I know this is a kind of old post but ...

How big is this thing supposed to be? A valve from a forklift is going to be pretty pricey. If the system is small you could switch to a butane lighter. It takes fairly little pressure to open the valve and the travel is only a few mm from full closed to full open (and it defaults to full closed). I would think a generic model RC servo would have more than enough ooomph to operate a butane lighter's valve. For a buck you get both fuel and the valve.

And, you can adjust the maximum fuel flow from a disposable lighter over a pretty large range. See the bottom of the page at http://www.inpharmix.com/jps/Fuel%20Met ... ghter.html
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Re: Design help for propane valve

Unread postAuthor: Futterama » Tue Jul 12, 2016 2:45 pm

For some reason I didn't get an email with that last reply so I just noticed it now.
It needs to be lightweight and preferably homemade ;-) The lighter is way too small (not enough flow) and the pressure range has increased to 8-9 bar.
I ordered some cheap mini air blow guns on ebay, the type used for air compressors. It says copper/brass alloy in the listing but they were made from some low melting point aluminium. I was hoping to soft solder on them but had to give up. But I saved the internals, the system seems good, I just need to make my own housing and is currently waiting for a special tap size, also ordered on ebay, but it usually takes 4 weeks to arrive from China. But when i arrives I can make my own housing from aluminium.
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Re: Design help for propane valve

Unread postAuthor: Futterama » Sat Jul 30, 2016 3:58 pm

Special tap arrived from ebay and new aluminium for the lathe was ordered and I just made my own valve with some of the internal parts from the mini air blow guns. It works like a charm and does not seem to leak - only 30g!
Now I just need to figure out how I want to connect it to the RC servo. It needs to press straight down on the tap. I put a return spring inside the valve, so I only need the servo to push down. But with the pressure from the propane tank applied, it takes 2.5kg pressure on the tap to activate the valve. The servo I got for the job is a 3.5kg rated servo, so it should be able to do the job just fine if I do the mechanical link the right way.
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Re: Design help for propane valve

Unread postAuthor: Futterama » Wed Aug 03, 2016 3:57 pm

Now with servo operation :D

The servo has no problem opening up even with a inlet pressure of 8 bar.

Total weight: 73g. I am very pleased with the result. Will fit my sound cannon project perfectly.

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