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Blowgun + 1" modified sprinkler valve

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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Blowgun + 1" modified sprinkler valve

Unread postAuthor: microman171 » Sun Nov 20, 2011 10:05 pm

I've done something wrong here. Standard blowgun (1/4" in 1/8" out) onto a modified sprinkler valve (has a spring inside) I bought from Mr Crowley. I pressurise to 50PSI or so, and then the blowgun lets all the pressure bleed out without actuating the cannon.

As a test, I replaced the blow gun with one of those quick connect self sealing connectors. When I pump to 50PSI, I jam a male quick connect in (allowing a 1/8" hole or so) which quickly vents the sprinkler valve, and then the main piston (which is 2").

What can I do with the blow gun to try and fix this? I drilled out the input side (which had a 1/8" hole anyway, so probably made no difference), and slightly cut into the valve seat. It now leaks, but this should be fixable, and could just be some swarf in the seat.


Cheers,

MM
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Unread postAuthor: Gun Freak » Sun Nov 20, 2011 10:14 pm

You should probably upgrade the pilot valve. I don't know why it wouldn't work though, I've done the same thing successfully multiple times.
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Unread postAuthor: MrCrowley » Sun Nov 20, 2011 11:20 pm

Strange, you'd think if the valve works with a solenoid it should work with a blowgun. How big is the pilot volume of your 2" piston? I'm just thinking that if the sprinkler valve is connected literally directly behind the piston, at 50PSI there might not be enough air between the piston and sprinkler valve but I've never heard of a problem like that before.

It's also odd that the sprinkler valve drains the chamber of the piston cannon as well, this could indicate your piston is not a good enough fit inside its housing and needs to be replaced/modified. If the blowgun is draining air between piston and sprinkler valve, the piston should still actuate regardless of whether the air drains through the blowgun or sprinkler valve.
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Unread postAuthor: microman171 » Sun Nov 20, 2011 11:32 pm

The piston activates fine with a 1/2" ballvalve. The fit between the wall is close enough that I can actuate the piston using my mouth (Mmmm, CRC..!)

I think the problem is that the blowgun isn't piloting the sprinkler valve fast enough. However, this seems strange since a solenoid can open it though a very tiny hole...
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Unread postAuthor: MrCrowley » Sun Nov 20, 2011 11:40 pm

Perhaps locate the equalisation hole on the diaphragm and epoxy it up and make a smaller hole. If the hole seems small enough, than don't bother.

The only other thing that could be an issue that I can think of is if you left the nozzle (the bit on the right with the hole in it) on the blowgun.
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Unread postAuthor: microman171 » Mon Nov 21, 2011 12:16 am

The blowgun is a cheap one from mitre10 that came in this kit: http://www.mitre10mega.co.nz/shop/power ... it_260684/ except mine is a smaller kit made by the same people (16 accessory instead of 20)

I will try reducing the hole to a smaller one (it's about 1.5mm).
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Unread postAuthor: microman171 » Mon Nov 21, 2011 11:43 pm

Okay, after filling the equalisation hole on the sprinkler valve's diaphragm with epoxy, and redrilling to 0.7mm (I drill a lot of PCBs, and have all sorts of small drills :-D ) the cannon now works great.

When I drilled out the blow gun to try to increase flow, I ended up drilling into a valve seat which stopped the valve working. I managed to fix this by putting a steel washer to create a new seat. I've bent a few washers after tightening down the valve too far, but as long as I don't tighten it to the point of bending the washer it will work.

So the cannon works great! There is a VERY large pilot volume created after I used 1" fittings, so I plan to do this: Image without the pressure gauge (I don't really need it)
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Last edited by microman171 on Mon Nov 21, 2011 11:58 pm, edited 1 time in total.

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Unread postAuthor: MrCrowley » Mon Nov 21, 2011 11:47 pm

Glad to hear it works and that my valve has found a new owner who doesn't leave it sitting in a box for ~2 years :D

Any preliminary pics of the cannon?
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Unread postAuthor: microman171 » Tue Nov 22, 2011 12:29 am

Consider these the prelimary pictures... :-)

Image

Image
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 22, 2011 12:36 am

Shame about the extra tee just for the sake of the schrader. Consider the following:

- remove the tee and attach the sprinkler directly to the end of the chamber
- remove the shrader core
- attach the shrader body to the outlet part of the blowgun

For filling, simply hold the blowgun open, letting it close before removing the connection with the schrader.

Voila, dramatic reduction in pilot voluume.
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Unread postAuthor: microman171 » Tue Nov 22, 2011 12:51 am

I wish it were that simple... The blowgun valve is broken to the point where air coming from the 1/8" side will leak out the valve lever. Fortunatly, I managed to salvage the valve enough that the 1/4" side was air tight.

I need to add the shraeder to the sprinkler body, possibly in a hole below the blowgun. I think this will be the only real way to remove that tee (which was surprisingly cheap, like $6! I was amazed at that...)

Another option would be out the side of the 50mm socket, but I don't like that idea...
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