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sprinkler valve dwell

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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sprinkler valve dwell

Unread postAuthor: F.E.A.R._Sniper » Mon Aug 11, 2008 12:12 pm

how low is it possible to set the dwell on a sprinkler valve?

9ms total open time?

i am just wondering for a project paintball rifle
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Re: sprinkler valve dwell

Unread postAuthor: starman » Mon Aug 11, 2008 12:36 pm

F.E.A.R._Sniper wrote:how low is it possible to set the dwell on a sprinkler valve?

9ms total open time?

i am just wondering for a project paintball rifle


Dwell? There's no settings like that that I know of. The valve will stay open as long as you actuate it.
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Unread postAuthor: F.E.A.R._Sniper » Mon Aug 11, 2008 12:40 pm

i was gonna use a board to control it, so it will have an automatic dwell
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Unread postAuthor: BC Pneumatics » Mon Aug 11, 2008 12:44 pm

"Dwell Time" is the time the valve spends open. As long as you apply current, the valve will stay open. However keeping a valve open longer than it takes for the projectile to leave the barrel does not help anything, so you will not have to keep it open terribly long unless you are using it in some unique way.
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Unread postAuthor: jimmy101 » Mon Aug 11, 2008 1:07 pm

Depending on the size and construction of the valve a 9ms dwell might be doable. That's about 110Hz (assuming equal open and closed times).

You might have to actually switch the current off before 9mS since the valve probably closes pretty slowly. Indeed, a water valve would be designed to close slowly to prevent water hammer. Not sure how slow "slowly" is though.
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Unread postAuthor: BC Pneumatics » Mon Aug 11, 2008 2:28 pm

Let's not forget the the open/close of the solenoid is relatively (relative to 9ms) far removed from the actual opening and closing of the valve.
9ms is right in the range that we use for open/close time of electronic sprinklers in GGDT. This means it should be about possible, but the solenoid will retract (open) quickly, then spend longer re extending (closing). You will have to account for this in your timing (which should be dynamic, and tuned in rather than calculated and set as a static system IMHO) and also must realize that the valve is theoretically only fully open at the apex of the solenoid's travel, meaning flow with a 0ms dwell valve (since all time open occupies the actual opening/closing phase) will be dismal.
I think that if you offered us more details about your project, we could be much more helpful. Also make sure you ran this through GGDT, it will show you a lot of the fun stuff that happens when you tweak open/close/dwell times. I would take a look, but alas, there is no GGDT.tar.gz ;)
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Unread postAuthor: psycix » Tue Aug 12, 2008 3:10 pm

The valve may close and open too slow for that, but it should be do-able. Fill from the pilot to close it faster and instead of pilotting with a solenoid, you could pilot with a QEV pilotted by the solenoid.
Then, its just all about tweaking. You should try every possible setting, and find out what works best.
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Unread postAuthor: jimmy101 » Tue Aug 12, 2008 3:53 pm

Another thing to consider would be to lengthen the ~9mS dwell time. I assume you want the gun to fire once every 2x9mS. That'd be a ROF of 56 rounds/second (3300 rounds/minute) which is really to fast to be of much use.

Change the dwell so you are firing at a more "leasurely" rate of perhaps 5 rounds/second (300 RPM). Perhaps something like 0.02sec open, 0.18sec closed. That'll give you more time to get the valve opened and closed and give the air supply system more time to recover between shots. I think you'll be much happier with a significantly higher muzzle velocity than with the impratically high ROF and the high ROF's much lower muzzle velocity.

IIRC, there are ways to wire up a 555 timer so that you can change both the frequency and the duty cycle. That'll allow you to change both the ROF and how the cylce time is partitioned between valve-open and valve-closed times.
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Unread postAuthor: F.E.A.R._Sniper » Tue Aug 12, 2008 6:07 pm

well my project is a paintball rifle with a sprinkler valve as the whole valve set up. i was gonna use a paintball board that i can adjust the dwell on for this since i know when i plugged it into GGDT diff. temps. required a different dwell to achieve close to 300 fps
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