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Modified Sprinkler Valve Trouble Shooting

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Modified Sprinkler Valve Trouble Shooting

Unread postAuthor: Will_U_Phistme » Tue Feb 27, 2007 5:50 am

My sprinkler valve does not work. On firing at 40psi, air just blows out of the airgun, without launching anything. Can you please read my story, look at the photos and offer me some advice.

I modified a sprinkler valve, a Rainmaker 1 inch model (Photo 1). Although I read the tutorial on modifying such valves, I took the essence of that advice but mounted the blowgun not on the sprinkler valve cap but on the solenoid mounting.

I did this because I feared that over time, kick back translated though the blowgun would undermine the threaded plastic seat for the blow gun, and thus loosen the mounting. Blow guns have small tight threads illsuited to tapping into softer materials like plastic, and can vulnerable to damage from normal wear and tear.

Mindful that the modification works on the principle of massively depressurising the upper chamber of the sprinkler valve, thus causing the diaphram to collapse away from force and simultaneously unsealing the outlet, I tried to maximise airflow to the airgun. I tried to minimise narrow spaces, the bottlenecks which might slow airflow from the upper chamber to the airgun.

Here is a description of how the air moves to the blowgun. I bored out the port leading from the upper chamber of the sprinkler valve to the solenoid mounting (where my blow gun is seated). I bored the port out to 4 millimetres. See photo 2. The blowgun is screwed into the solenoid mounting via two plastic adaptors. Each adaptor has at least a centimetre diameter of internal space. The lower and larger plastic adaptor that is screwed into the solenoid mounting sits 4-5 millimetres above the port from the upper chamber. The blowgun's bore is at the narrowest point 6 millimetres in diameter.

My first problem was that the gun would not pressurise and air escaped under the diaphram and through the outlet instead of seaping through the equalisation hole in the diaphram. Spudwiki suggested that some people remove the white plastic plug from the equalisation hole to increase air flow during pressurisation when the air is pumped in. That is what I did. See photo 3. It solved the problem, and I was able to start filling the chamber/tank of the gun.

So what is the problem? Now when I press the release button on the airgun, air rushes out of the airgun. But the diaphram does not open.

Just so you know, I have cleaned the diaphram and seat in the valve. The bleed screw and other solenoid ports have been blocked.

My theories? That the equalisation hole is now too large. On firing, air can drain out of the equalisation hole, through the upper chamber of the sprinkler valve and out the airgun without activating the diaphram. Or conversely, the passages to the airgun are too narrow, and thus the airgun cannot release enough air quickly enough to depressurise the upper chamber and activate the diaphram.

I don't want to install the airgun into the cap of the sprinkler valve, for the reason noted earlier.

What are my options? Make the equalisation hole smaller, and/or enlarge the passage to the airgun? Any other options?

Your advice will be gratefully received.
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Attachments
PICT0012.JPG
Photo 2. View of sprinkler valve cap. The port to where the solenoid used to be has been bored out to 4ml.
PICT0013.JPG
Photo 3. This is the diaphram. I have removed the white plastic piece from the equalisation hole. The equalisation hole is now about 2-2.5 millimetres in diameter.

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Unread postAuthor: Matheusilla » Tue Feb 27, 2007 5:46 pm

Smaller equalization hole, quite obviously. If the equalization hole is larger than the smallest restriction through the blowgun it will continue to equalize the pressure. Did you leave the large spring in? If you left it out, or weakened it, the diaphragm may not close.

Although, I did buy a defective valve one time, It's a possibility.
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Unread postAuthor: noname » Tue Feb 27, 2007 8:29 pm

Cover up half the equilization hole with electrical tape, if it works, good for you, if it doesn't, then go back to trying to fix it.
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Unread postAuthor: spudthug » Tue Feb 27, 2007 10:50 pm

i would cover it up half like noname said but also try to get the electrical tape really tight or it wont work...either that or use some top product tape that never comes off.......if you are using electrical tape dont buy the crappy ul stuff buy scoth 3m works alot better....mmk
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Unread postAuthor: noname » Wed Feb 28, 2007 1:05 am

Use whatever you have on hand. If it works, use something more permanent.
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Unread postAuthor: killagorrila99 » Wed Feb 28, 2007 2:16 am

Get a peice of thick wire about an inch long, Bend on end of it on a right angle so that the bent peice is about 3-4mm long. Insert this wire into the equalisation hole and bend the other end of the wire so it is perminantley stuck in the diphragm. And use a spring for corns sake.
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