Question about sprinkler valves?

I'm planning on making a potato cannon, however I want to make it be able shoot multiple times with one tank. If I make the firing valve a pneumatically powered sprinkler valve, will it have to empty the entire air tank before it can close? Or can I just release the trigger and have the valve close with still some air in the tank? I'm already going to have a 2 tank design with a firing tank and a primary air tank.

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You will need 2 tanks and 2 valves for this. The Primary tank will be the main tank that holds all the air. The secondary tank will be much smaller and only hold enough air to fire the cannon. Use a manual valve between the 2 tanks. You'll have to reload the cannon so you can take the extra step of turning that valve by hand. Then you can have a nice electronic valve between the secondary tank ant the firing tube.

A quick open and shut of the main valve shouldn't dump the contains of the primary tank into the secondary tank. just don't leave the valve fully open. Leaving this hand operated is probably best as you learn how far and how quickly the valve should be opened to get the better shot.
bwrussell5 years ago
Use Arduino like THESE guys did. You could replace the android interface with trigger switches but the remote triggering is safer. With the Arduino you could program in the entire firing sequence: pull trigger, open barrel valve, close barrel valve, open refill valve, close refill valve. They programed there's to close right after shooting to keep some air in. Not sure how well that worked but worth a try.
General Eggs (author)  bwrussell5 years ago
The only problem with that is I'm trying to keep it low in cost AND only have one barrel. I'm trying to make it handheld.
Exactly, with one barrel and two tanks you are using two valves, just like the example. The only difference is the timing. The only additional cost is a $30 Arduino which will simplify the build and make firing the canon a breeze. I wasn't suggesting creating the exact same thing, just adapt their idea of using arduino to control the valves to your need.
General Eggs (author)  bwrussell5 years ago
ok, I never really did look up how much arduino costs, but it seems if I keep the trigger electronic, but make the valve open faster than an unmodded valve, it would work really well.
not entirely sure what you mean here, I've never worked with these sprinkler valves. If you can mod them to open and close faster that would improve performance of both the firing and the refill. You will have to experiment to discover exactly how long to open the valves for both firing and for refill.

Be careful, the refill chamber will have to be under a lot of pressure. I would suggest making it out of metal or some other pressure rated pipe, not PVC. This will also give you a lot more shots at the expense of weight and a little cost, or the refill container could be a paintball air tank.
General Eggs (author)  bwrussell5 years ago
ok, ill try that
Re-design5 years ago
Any valve that will open wide enough to fire will empty the tank also. I don't think you can get it to operate fast enough. At best you would waste several shots worth. You need to build a two tank design. A holding tank would fill a firing tank.