spud gun/T-shirt gun valve

[EricH]

Just to further explain the danger of compressed air:

A sufficient volume of air at single-digit IWC (Inches of Water Column) can, if released suddenly, make its presence known throughout a brand-new building (by shaking if I recall correctly) with the building's biggest door wide open to vent any sudden releases of air straight outside. I wasn't in that building at the time--but I heard about it.

1 IWC = 0.036 PSI per Google's converter (I rounded).



And the item containing said air was, in fact, rated for gases.

[FrankJ]

We use an Asco 2/2 series main pulse valve. 8353C035. It is intended for back pulsing dust collectors. High flow rate & fast acting.

[hank2247]

For what it's worth, my team has been using 1" sprinkler solenoids on our T-shirt cannon robot for over 3 years without any problems from the valves. (We use them up to 120 Psi)

[GeeTwo]

Originally Posted by hank2247

For what it's worth, my team has been using 1" sprinkler solenoids on our T-shirt cannon robot for over 3 years without any problems from the valves. (We use them up to 120 Psi)

NASA ran over 100 shuttle missions before a chunk of shuttle insulation struck the leading wing edge, resulting in the demise of Columbia and her crew. Just because you get a way with something for a while doesn't make it safe.

[hank2247]

True, but everything on the cannon is rated for a much greater pressure than we ever put through it including the sprinkler valve. we also have built in points of failure to avoid any PVC explosions or fragmentation. (pressure cylinders are not made from PVC)

[Mr V]

The other thing that no one has brought up concerning PVC is that it is degraded by UV rays by making it even more brittle. Like all plastics it also off gasses, also increasing its brittleness. So the risk of failure increases with time.

[Mykey]

I will not repeat the value of having the correct materials for the job - safety first!

That being said, many of the valves we are talking about have a diaphragm in them that is held in place using a spring. If you change (lower) the pressure applied by the spring it results in a more abrupt and greater release of air flow. If you lower it too much then the valve lets go on its own when the pressure reaches the lowered break point.

So... replace the spring with a weaker one. Or the "poor teams" method is to clip small pieces off of the spring bit by bit until it has the pressure setting you want.

[GeeTwo]

Originally Posted by Mykey

So... replace the spring with a weaker one. Or the "poor teams" method is to clip small pieces off of the spring bit by bit until it has the pressure setting you want.

And my advice is not to do this - get the right thing to start with, unless you know what you're doing (and by that I mean certified). There's a reason that FRC rules do not permit any modification of pneumatic devices, apart from cutting tubing and making adjustments that were specifically designed to be adjusted by the user/consumer. You got it in one: .

[Mykey]

Originally Posted by GeeTwo

And my advice is not to do this - get the right thing to start with, unless you know what you're doing (and by that I mean certified). There's a reason that FRC rules do not permit any modification of pneumatic devices, apart from cutting tubing and making adjustments that were specifically designed to be adjusted by the user/consumer. You got it in one: .

You are correct. It is by far better to have the correct component from the start. The high pressure hydraulic systems I am responsible for are bad enough. Pneumatics are a whole new level of scary. On reflection it is not a good idea for the average person to play with the inner workings of a valve system.

Unfortunately, the majority of T-shirt launchers are not based on well engineered designs. They seem to be based on you-tube videos and the desire to shoot things. Thankfully most of us who have managed to make it to adulthood have managed to suppress the urges that led us to playing with fireworks, slingshots, pea shooters and home made darts.

Although, I have to admit I still have some of that garage inventor in my blood... must resist the urge...

To those who will be making T-shirt launchers: They are inherently dangerous. Please o' please if you are doing this stay conservative (high pressure ratings for lower pressure applications)!

[FrankJ]

Originally Posted by GeeTwo

And my advice is not to do this - get the right thing to start with, unless you know what you're doing (and by that I mean certified).

I will bite. So how did you get certified?

[GeeTwo]

Originally Posted by FrankJ

I will bite. So how did you get certified?

Sorry, did I imply that I was certified for pneumatics work? One of our mentors, Isaac, is a certified pneumatics tech for Ingersoll Rand. While we've never spoken at length about it, I understood that there was a combination of course work, practical, OJT involved. I'm just a physicist who can crunch enough numbers to know that this is too ugly for a jack-of-all-trades to play around with.

I never had a biology course after high school, but I also advise that you don't perform surgery on your family members without the appropriate medical certifications.

[FrankJ]

Originally Posted by GeeTwo

Sorry, did I imply that I was certified for pneumatics work? One of our mentors, Isaac, is a certified pneumatics tech for Ingersoll Rand. While we've never spoken at length about it, I understood that there was a combination of course work, practical, OJT involved. I'm just a physicist who can crunch enough numbers to know that this is too ugly for a jack-of-all-trades to play around with.

I never had a biology course after high school, but I also advise that you don't perform surgery on your family members without the appropriate medical certifications.

Sorry I was not questioning your credentials, although it does read like that. From your posts, you seem well informed about what you write about. I meant to how does some one get certified in pneumatics in general.

Generally speaking techs work from a set of rules where engineers are able to work from first principles. In the real world this can get very blurry. I know techs & mechanics that know for more about their specific subject than the engineers that are supervising them. The world needs both kinds & hopefully that is what we are developing.

[fovea1959]

to all: thanks for all the input and discussion. We scrapped the PVC tanks and valves (kept PVC barrels), went to steel 1/2 gallon air tanks (holed sawed a hole in one end to remove the 3/8" fitting and had a 3/4" or 1" bung heliarc'd in). Valves are 12V metal valves (used for clearing the bags in dust collection systems?).

MrBasse shared a photo album with *their* shooter, and gave permission for me to link to the album. They have "cartridges" that they can preload... https://drive.google.com/folderview?...&usp=sha ring

I'll post pictures of where we ended up after scrapping the PVC tanks and valves.

[Daniel_LaFleur]

Originally Posted by hank2247

True, but everything on the cannon is rated for a much greater pressure than we ever put through it including the sprinkler valve. we also have built in points of failure to avoid any PVC explosions or fragmentation. (pressure cylinders are not made from PVC)

1> everything but the PVC parts may be rated for high pressure, but PVC is NOT rated for gas.

2> universal gas laws -- pressure is exerted on all surfaces equally. Thus your PVC parts are seeing the same pressure as all other items regardless of their pressure ratings.

3> T-Shirt cannons are, by design, to be near the public (within shooting distance). Knowingly using non-gas rated parts in a gas (air) cannon may be gross negligence should something happen (I'm not a lawyer but this seems a reasonable argument).

All I'm saying is in this lawsuit culture, you may want to consider overdesigning a bit for safety.

[hank2247]

the sprinkler solenoids are rated for 150 psi