First Design, T-shirt Cannon, feedback on my initial design.

[garybdavis]

I’m starting my first built which will be a pneumatic t-shirt cannon. After a few days of reading through various builds in this forum here is what I’ve settled on:

1”x4” Steel Pressure Chamber (galvanized pipe)
3”x18” Barrel (PVC - pressure rated)
¾” QEV (the one from McMaster-Carr seems to be the most popular)
100psi Maximum Shooting Pressure (limit of the QEV is 125psi)
150psi pop-off safety valve
Palmer Female Stabilizer (0-200psi output, 3kpsi max input, 90 degree version)
HPA tank, 48ci, 3000k aluminum
¾ Slider Valve
Pneumatic blow gun trigger

I’m planning on using a slider valve in between the regulator output and the pilot of the QEV. I’ll plug the nipple between the two and drill a small orifice hole to let the air bleed a bit slowly from the HPA tank into the pressure chamber. The idea is after each shot, you open the slider and fill the pressure chamber to your target pressure. So, if you want a short range shot, fill it to 40psi and let it fly. Then, open the slider valve and fill it to whatever pressure you want for your next shot - say 80psi to reach the back of the stands. The operator watches the gauge on the pressure chamber while holding the slide valve open. The plug/orifice hole slows the fill rate down to make it more manageable. I’m sure someone has built one like this, I just haven’t found one.

I read a post from one member who used these parameters and said he can shoot a shirt up to 200 ft. I tired to model this in GGDT, but can’t get it to clear errors/warnings, much less go 200ft. I weighed a t-shirt and it was about 220gm which is what I’m using for my projectile weight. I guess I don’t know enough of the parameters to get the inputs correct. If anyone could show me a screen shot of how GGDT should be configured to model this gun, it would be appreciated.

Below is a rough schematic of the cannon (maybe because I'm a newbie, it won't let me attache a pic yet). I’m holding off on ordering the major components (QEV, Palmer stabilizer, slider valve, etc) until I receive some feedback from you guys (hopefully). The only source I haven’t settled on is slider valve. I need to check McMaster-Carr before I get one from China off of ebay.

Any feedback would be helpful. Thanks!

[jrrdw]

"(maybe because I'm a newbie, it won't let me attache a pic yet)."

If the file manager wont upload a picture from your computer it is either to big or the wrong format.

Who's model are you following? Technician1002?

Welcome to Spudfiles.

[garybdavis]

The pic is a 46k jpg file. It gives me this error: Sorry, but the maximum filesize for all Attachments is reached. Please contact the Board Administrator if you have questions.

I'm not sure who's model I'm folloing. I've copied so many pictures and comments to my notes that I don't know which side is up anymore. The size of the pressure chamber, barrel and 3/4 QEV is a combo someone on this board came up with. Using the slider valve to charge the pressure chamber is my own thought (although I'm sure it's not orginal).

I still get the same pic upload error. I'm sure of my capability to resize photos, just doesn't seem to work for me here.

[jrrdw]

"I still get the same pic upload error. I'm sure of my capability to resize photos, just doesn't seem to work for me here."

You don't live in a epoxy cave do you? Joking, your not the 1st to get that error message, I'll contact the administration to see what's going on with that. Sit tight and you'll start getting feed back on the cannon plans. From your discription, this sounds like Tech's slide valve...

[Technician1002]

It doesn't sound like my design from the parts list. I presume the chamber is a foot by 4 inch instead of 1 inch by 4 inch.

It sounds like a chamber, a 3/4 inch QEV and 18 inch long 3 inch barrel. The other parts are for charging.

If that is the design, I would expect the maximum range at 100 PSI to be about 75-100 feet with a rolled up shirt. The 3/4 inch QEV is too small to provide the high flow required.

What range do you need with the launcher?

[garybdavis]

The pressure chamber is 1 inch galvanized steel pipe that is 4 inches long. I'd post a picture of the one I'm modeling it after, but the attachment function is not working for me.

I'd like to be able to shoot it a 100 ft or so with a nice arc.

[MrCrowley]

A 1" chamber 4" long will do nearly nothing at 100PSI. I doubt the t-shirt would leave the barrel.

The smallest chamber you could go with at that pressure is probably 2" diameter 12" long. With a 3/4" QEV, that might be enough for 100-150'.

edit:

as for posting images:
http://www.spudfiles.com/forums/posting ... 13190.html

[garybdavis]

Well so much for that idea...back to the drawing board. I have a pic of a cannon that has a 1in x 4in steel pipe, 3/4 QEV and 2.5in x 15in barrel. Maybe it was for something lighter like confetti instead of a t-shirt?

[MrCrowley]

Or it may have used much higher pressures. Can't imagine the reasoning behind using such a small metal chamber for only 100PSI. Even for confetti, it would be pretty weak.

[garybdavis]

So, do they make 3/4 QEV that are rated higher than 125psi? That's what the one from McMaster-Carr is listed at. The steel chamber, QEV and slide valve would all have to be rated for a higher pressure.

[MrCrowley]

I take my 3/4" past 300PSI regularly, some have even exceeded 500PSI. If you're keeping to 500PSI and below, the worse that is going to happen is that the diaphragm will fail/leak. Adhere to safety standards like "always point the cannon in a safe direction" and "once pressurized, assume the cannon may fire unexpectedly" and you'll be pretty safe. Basically, a failed diaphragm will cause the gun to fire.

I can't comment on slide valves in particular but I'm sure some members have taken cheap ones up to 300PSI (and beyond perhaps) without trouble. They're basically a sleeve that moves over some o-rings. There's not much that can go wrong. Most metal components like that can take 300PSI even if they are not rated for it. However, it would be best if you upload a picture or show us the model first.

The chamber shouldn't be a problem. Malleable galvanised iron pipe and fittings from the hardware store are rated for 150PSI working pressure but can take ~500PSI safely. I use 2" pipe and fittings in a hybrid cannon that see momentary (milliseconds) spikes of pressures near 1000PSI. I wouldn't go as far as recommending these fittings to hold 1000PSI for longer periods of time, but at 500PSI it is probably safer than using PVC at 100PSI.

[garybdavis]

Can you give me some general guidelines for a t-shirt launcher as I seem a bit lost. I just don't have the experience you guys do (and I want to be safe). I'm not a fan of PVC and plastic sprinkler valves. I'd like to use steel for the pressure chamber and a QEV so I can get more efficiency with a higher pressure and be more compact. At least that is what I understand at this point.

Thanks

[Lockednloaded]

You can use your design, you'll just need to pump up the pressure



Here's one I made with a 1/4" slide valve piloting a 3/4" QEV with a 1"x5" chamber and about a foot of 2.5" conduit for the barrel

[garybdavis]

Sweet. That's very close to what I have planned! I went back and found the post of the one I liked and it was a pic you posted.

http://www.spudfiles.com/forums/viewtop ... 7e7379b77f

Now for a few questions if you don't mind.

What pressure are you running (I'm guessing 450)?
How did you connect the conduit and is it EMT?
Is that the 3/4" QEV from McMaster?

I don't understand the slide valve and ball valve in series. It may be that I misunderstand the function of a slide valve. It think it works just like a ball valve where it passes air as long as you hold it open. But from the video I found, it seems to pass a burst of air then shuts off. Or perhaps the tank is only hooked up to charge the cannon and disconnected to shoot?

[Lockednloaded]

I've actually run it at 700 psi a few times, but I you should be fine running it around 300 psi for some decent performance.

I epoxy'd a 3/4" female coupling in, but another, better way to do it would be to just epoxy in a 2" PVC bushing in that reduces down to 3/4" female threads.

Yes the QEV is from McMaster

The ball valve is just because my fill valve doesn't have a check valve on it