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Sprinkler Valve Opens While Pressurizing

A place to ask general spud cannon related questions.
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Sprinkler Valve Opens While Pressurizing

Unread postAuthor: AegisAvenger » Sun Mar 08, 2009 4:06 pm

Hi all, I recently built an arm mounted spud gun. It has an interchangeable barrel. One barrel is for shooting projectiles, the other is a nozzle for firing water out of the cannon.
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I'm having a problem with the water.

I'm using an Orbit Sprinkler valve, powered by three 9v batteries. There is a dual Safety Switch system to prevent any chance of accidental firing, and all wires are accounted for.

I have a fill chamber about the size of a water bottle with a fill cap on it. That's where I pour the water into, and also where the schrader valve is.

That chamber is connected to the sprinkler valve by a 4 inch hose.

No matter how much or how little water is put into the chamber, the valve always opens by itself while I'm pressurizing the cannon!! By this I mean that when I push down on my bike pump, there's a squirt of water coming out the barrel of the cannon.

I noticed that once I get to 20 psi, the valve closes, and I can continue pumping without a problem.

Does anybody know if this is just a safety feature on the sprinkler valve?? And if so, is there a way around it, or a valve out there known to NOT have this feature??


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Unread postAuthor: psycix » Sun Mar 08, 2009 5:20 pm

A piston or diaphragm valve needs pressure to seal because it needs a force to press the diaphragm down.
Some valves seal at a few psi, others need more then 30.
This is mostly defined by the surface area of the sealing face, the material and the quality of the sealing face and the geometry and quality of the rim it is pressed against.

Maybe you can open up your valve and clean it. Most of the times this fixes sealing problems.
You can also hold it upside down so that everything that leaks below 20psi is just air and no water.
Another thing that can help is adding a spring. This will give you that extra force you need to seal.(or when there already is one, strengthening it)

Some thoughts I have on seeing that gun:
-The hose. Not very flow-efficient is it? Why not just take two elbows?
-You electronic actuation. Why no blowgun? Electronics are usually not waterproof (or hard to make that) and a modded valve can practically work underwater. Also, its more powerful.
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Unread postAuthor: sgort87 » Sun Mar 08, 2009 5:54 pm

There's a little white thing that's stuck in the rubber diaphragm. Make sure you pull it out. It might be the source of your problem.
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Unread postAuthor: Hubb » Tue Mar 10, 2009 7:43 am

I would say your bike pump is the problem.

You need to put more pressure in the diaphragm faster than what you're doing. This can be done one of several ways. 1) Put a ball valve between the chamber and valve, open when chamber has some pressure in it, 2) use a compressor, or 3) put your air intake in the pilot area.
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