How to inspectors test compressed air tanks and steam boilers? They fill them with water and hydro test them. If the tanks fail, they just split and water squirts out and falls to the ground. When a steam boiler ruptures with steam, bad things happen. http://lubbockonline.com/stories/073001/upd_075-5251.shtml#.VeNOZvlViko
When using piping or valves, check for the “WOGS” rating. W= Water, O=oil, G= Gas, and S=Steam. Some valves might have 100W 60GO 40S, meaning 100psi for water, and 60psi for both oil or gas, and 40psi for steam.
So in short, 100psw water is not the same as 100psi Steam, nor 100psi Oil, and not 100psi Gas. You can have a really bad day if you mix them.
I had a neighbor use plastic water pipe to plumb his garage shop, it was left over from replacing his water feed lines in the house. The house pressure was 65psi and rated for 100psi. He ran 80psi air in the same pipe. One day there was a large bang as he was working in the garage. They took a 3" long peice of the plastic pipe out of his chest. Needless to say, when he recovered out went the plastic pipe and in went black pipe.
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.
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.
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.
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: ::safety:: .
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)!
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.
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?).
Compressed gas does have more energy than compressed liquid, but the force exerted on the valve is the same. Pressure is pressure, air just compresses significantly more than liquid so its potential energy under pressure is much greater.