# Air Cannon Firing Issue



## GhoulishCop (Sep 25, 2009)

Hey folks,

Maybe you can help me with an issue I've been having with my newly built air cannon.










Not shown in the photo above are the solenoid and "horn" attached. The big gray mass at the top of the piping is a dump valve. That was used instead of a sprinkler valve.

It's all hooked up properly because it works...intermittently. And that's the problem.

I pressurize the tank to 80 psi and am able to fire off a consecutive series of rounds on the cannon, all the way down to 40 psi, after which the air just discharges from the solenoid. I then allow it to re-pressurize to 80 psi (or 90+ even) and the air simply exhausts without firing.

Only after I completely empty the tank and then re-pressurize it to 80 psi am I able to fire it again.

Does anyone know why this might be happening? It almost seems as if the valve is sticking in the open (closed?) position and it's not until the pressure is completely dissipated that it's able to close (or open). Then again, I have zero knowledge of how these things work, so it might be something completely different.

It's a very cool toy, er, prop when it works but right now the intermittent nature of its operation is frustrating. Thanks for any help anyone can provide.

Rich


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## imax (May 22, 2006)

What's the make and model of that dump valve? The datasheet for it might give us a clue.


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## GhoulishCop (Sep 25, 2009)

imax,

It's a Detrol EV35A2 quick exhaust valve. It was generally working okay when the cannon was built on Saturday, and though cool out, was somewhat warmer than it was today. It had a few misfires then, but typically when the pressure was above 80 psi would fire on cue.

The tank also sat outside from Saturday till today and the temps have been appreciably colder than they were then.

Niblique71 thinks it may be those cooler temps affecting it since the valve essentially has a rubber gasket of sorts inside that opens and closes and it might have stiffened up in the cold weather. He's not certain though and is checking too.

I just checked out the specs sheet for the valve at hydraulicstore.com where I purchased it, and it says it has an operating temperature of 0-240 degrees F. Theoretically it should work.

http://www.hydraulicstore.com/images/pdf/deltrol_quick_exhaust_valves.pdf

Any assistance would be appreciated. Cheers,

Rich


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## niblique71 (Dec 2, 2009)

Hey Rich,

Jeff has already responded, although I don't think he realized that on saturday I DID have the air pressure up to the cannon's (Tank) max of 125. I suspected that the issue you were experianceing was a combination of cold air AND Low air pressure. In My letter to Him I described that you running like 90psi (is that the case?). If so, That's 35psi lower than what we were running on saturday.

Anyway, He'res what he said.


> Hey Greg,
> 
> I can't say for sure as I've never tried it at low pressures. These are
> high pressure industrial dump valves and I have never even thought to run my
> ...


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## GhoulishCop (Sep 25, 2009)

Wow, Jeff is responsive! I will say I was actually having problems with both my compressors today getting them up to even 80-90 psi. They were taking forever! 

The larger compressor I have, which says it goes to a max of 125 psi (a Lowe's Kobalt model that's admittedly been thru hell) was struggling more than my Porter-Cable pancake compressor. Both definitely did not approach 100 psi though. I'd say 90 or so was the max they were hitting.

So, as you first suggested, it might be time for a new compressor. Awesome! I was at Harbor Freight Tools yesterday and saw some models that I was tempted to buy without even having a need, and having to shoot off an air cannon is definitely no luxury. It's a freakin' necessity.

The worst that happens with this is I have a new compressor. Seems like a win-win situation! Thanks, and if anyone else still wants to chime in thinking it might be something else, please feel free to do so.

Rich


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## Gory Corey (Nov 17, 2006)

I see what appears to be adaptered from 1/2" to 3/4" for the QEV.
Questions: 
What size solenoid valve are you using?
What is the V rating of the QEV ?
What is the dump port size?


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## niblique71 (Dec 2, 2009)

We used a 1/4" 3-way selenoid, 

I'm not sure what the "V" rating is on the dump valve although it is an industrial 3/4" in/out.

Are you thinking that we need a larger ported selenoid to have the back pressure drop faster?


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## GhoulishCop (Sep 25, 2009)

Corey,

The inlet CV is 5.32 and the outlet CV is 7.84 with 3/4" ports all around.

http://www.hydraulicstore.com/images/pdf/deltrol_quick_exhaust_valves.pdf

The model we used is the EV35A2.

Rich


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## Gory Corey (Nov 17, 2006)

yes, look at the cv, and think of it as water flowing through a pipe (sorry my C key is facacked).

If your solenoid valve does not have comparable cv to the exhaust, the dump isnt efficient.
This can hang the QEV up.

That might explain why the compressor is having such a hard time, since air would be escaping the exhaust port concurrent with the inlet trying to fill the tank reservoir.

So which valve are you guys using?


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## niblique71 (Dec 2, 2009)

Rich, You're impressing me with your Research. Gory Cory, I'm beginning to think your right and we should have gone with a larger ported selenoid. Looking at the picture of the original Air Cannon design, the selenoid valve in his picture look to be at least one, if not two port sizes larger. I'll ask him what size it is his is again (Hmmmm, Don't go there Rich). His first reply was that it probably didn't matter. BUT if he already had a 3/8" or 1/2" selenoid, he wouldn't have experianced this problem, (assuming that this is the problem). I can also see that cold air would mildly affect the dump valve if the selenoid was borderline effective.

Now that I see exactly how the valve works internally, it makes sense why our tests were much more reliable at higher pressures with the 1/4" selenoid valve. I'm thinking that if Rich or Bob wants to run thiers at a lower pressures we can order a much larger ported selenoid. NOT to worry, You'll be able to use your other selenoids for other pneumatic projects with the right cylinder. I feel a little bad that we didn't absolutely NAIL this one. but I still feel that we'll havea superior product in the end.

I'm going to stick with my selenoid for now but would be happy to assist in the ordering and "Hack" if anyone else want's to go for a larger port size.


All I know is that was ULTRA Impressive at the MnT. The air volume was unbelievably intense.


EDIT:
Upon even closer inspection, it looks like Jeff has a 1/4" selenoid valve like ours. We are either facing a break in period, Air pressure issue, or cold weather issue because his works fine. Still I'll ask him what size his is to confirm, and then go from there.


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## GhoulishCop (Sep 25, 2009)

Greg,

I'd be willing to experiment with the different solenoid (might be cheaper at the moment than buying the new compressor ). And as you note, I can use the original with a different prop I'd build. No worries either way.

So....how do I get me one of these bad boys?

Also, Corey, if the solenoid's CV is "larger" than the valve, that's okay, right? It just can't be smaller?

Rich

*EDIT:* Okay, I just so your edit, Greg, so there doesn't seem to be a need to order a new one.


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## GhoulishCop (Sep 25, 2009)

And just for completeness, the solenoids that we used have a CV flow rate of 0.73-0.89 (depending on which website I'm looking at) with 53 SCFM @ 100 psi. 

I write that almost as if I know what it says.

Rich


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## niblique71 (Dec 2, 2009)

I was looking over some Stats for our Dump Valves

Tempature range is 0- 240 degrees F ..... Hmmm we were well within that range

Air pressure range is within 20- 125 psi, and we were right there, but found they wouldn't dump under 80psi.

Change in pressure (Delta pressure) is only 3psi to activate dump and our selenoids should have done that nicely at 1/4"

So now I'm not sure what was going on. Gory Cory seemed to be onto something with a larger selenoid valve (OR at least I think that's where he was going). These things should dump at 20psi reliably.


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## gadget-evilusions (Jan 26, 2007)

I have built close to 50 of these. A 1/4 " solenoid valve is on the fine line of having enough flow to exhaust quickly enough to operate the quick exhaust valve properly. Sometimes a valve will work consistently and then sometimes not. If you go with a 3/8 or 1/2 3 way solenoid valve, it will have no problem operating day in and out. Also, it appears you have the exhaust port reduced down. That can cause back pressure on the diaphragm an cause the quick exhaust valve to act oddly. Always leave the port marked exhaust as free flowing as possible.


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## niblique71 (Dec 2, 2009)

gadget-evilusions said:


> I have built close to 50 of these. A 1/4 " solenoid valve is on the fine line of having enough flow to exhaust quickly enough to operate the quick exhaust valve properly. Sometimes a valve will work consistently and then sometimes not. If you go with a 3/8 or 1/2 3 way solenoid valve, it will have no problem operating day in and out. Also, it appears you have the exhaust port reduced down. That can cause back pressure on the diaphragm an cause the quick exhaust valve to act oddly. Always leave the port marked exhaust as free flowing as possible.


Thanks G E,

What size do you use??

The 3/8" are reasonable $$, but 1/2" jump quite a bit in price. As long as you had good results with the 3/8", I'll suggest that we go that route.

PS:
The picture above was taken before we realized that we had the intake and exhaust on the dump valve reversed. That was corrected before we even tested the cannons.


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## gadget-evilusions (Jan 26, 2007)

3/8" solenoid valves work consistently good for me.


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