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Test plugs

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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Test plugs

Unread postAuthor: EGOed » Thu Oct 18, 2007 2:25 pm

Has anyone ever tried using test plugs for a removable plug in a tee , for use as a rear breach load for a sprinkler valve cannon ?..... This would be the type that fits inside 2" pvc and expands a rubber gasket inside the pipe as you tighten a wingnut on the test plug....It seems like they hold very tight when clamped properly and they are made for pressure testing pipeing systems..... Just wondering if anyone has tried this @ 100psi max and can tell me how well they work if at all....thanks
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Unread postAuthor: silverdooty » Thu Oct 18, 2007 2:30 pm

i have seen older ones wear out and eventually lose their grip. it was less than 100 psi.
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Unread postAuthor: meatballs » Thu Oct 18, 2007 2:37 pm

i wouldn't use one of these unless i did some experimentation or somebody else did to see what pressures they fail at with different diameters and how long they last and stuff. my gut feeling is that this wouldn't be safe but i honestly dont know.
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Unread postAuthor: williamfeldmann » Thu Oct 18, 2007 3:04 pm

Just so we are clear, the air flow will do something like the redish arrow and you want to put the test plug where the blueish arrow is pointing so you can have easy breech loading? That is how I will answer.

Image

I have also seen these test plugs wear out after time. However, if properly used they should hold ok for what you are doing since they don't actually hold any pressure except during firing.

You would get better performance out of a cleanout cap, though, I think. The screwing in action will hold better than the tension pressure of the plug. With a little creativity you could make the cleanout plug a much faster and finger friendly method as well (think extended handle for torque). Those test plug's wing nuts will wear out your fingers after a few loads.
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Unread postAuthor: EGOed » Thu Oct 18, 2007 3:27 pm

Your drawing is correct......My only reservations about using a threaded pvc cleanout plug is the wear on the pvc threads with frequent usage...These cannons are fixed artillary pieces on my paintball field and are fired close to a hundred times during one 8 hr scenario game ....My thoughts were the test plugs would hold up a little longer and are easily replaced when they do wear out.....The wingnuts will be modified and will have a handle to make tightening easier on the fingers ......My main concern was if they would blow out during firing.....Most shots with my present 5 ft. cannons are fired @ 60 psi or less to get within range of targets ....Two that I am building will have 8 ft barrells which will have even more range , but muzzle load is not an option ....Thanks for the help guys , just wanted to make sure it was an option I should consider experimenting with.
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Unread postAuthor: williamfeldmann » Thu Oct 18, 2007 3:38 pm

Yeah at 60ish psi you should be fine with the plugs, just don't stand behind the guns (duh, I know). As for the cleanouts wearing out, I would doubt that would happen very fast at all. What size barrels/ tees were you thinking of using? The bigger the barrel, the more reason I see for using the cleanout caps due to higher forces involved.
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Unread postAuthor: mark.f » Thu Oct 18, 2007 4:09 pm

What?

The only test plugs I have ever seen at most hardware stores are the type for testing gravity-drain systems like DWV systems for leaks. My guess is it would only be good for about 15-20 PSI max.
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Unread postAuthor: EGOed » Thu Oct 18, 2007 5:45 pm

Well , There are 2 different types of plugs that I have found...they both come in sizes from 1 to 4 inch diam.....The first 2" one I bought was red plastic flanges that expand the rubber gasket with a carriage bolt and wingnut...The second ones were metal flanges that work the same way....I dont know exactly what applications they are used for but it seems like they are overkill for gravity DWV systems.......I couldnt pound the metal test plug out of a short piece of 2"pvc by ramming a steel pipe into it with enough force that would easily shatter a pvc end cap or clean out plug....The thing didnt even budge and I still had room to tighten the wingnut even more......The mechanical clamping pressure must be far greater than 15 to 20 psi I would think ....I know I have tried rubber boot couplings as a temporary set up to test cannon barrells and they have stayed secure @ 100 psi with just pipe clamps holding them on the O.D . of pvc pipe....The test plugs seem to have much greater clamping pressure than that because of its internal design...... I will have to try them and see.
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Unread postAuthor: potatoflinger » Thu Oct 18, 2007 6:05 pm

Maybe you should just pressure test them with a short section of pipe (filled with water) with a test plug at each end and fill it up to around a hundred psi and let it sit for a while and if one blows, it's not safe. (I would at least leave it pressurized overnight). Also, make sure you keep it a safe distance away from anything it could harm if one did blow.
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Unread postAuthor: EGOed » Thu Oct 18, 2007 6:19 pm

I will just go ahead and make the cannons and just leave enough pipe exposed out of the tee in case the test plugs dont work out....That way I can just solvent weld a cleanout plug adapter on the tee if I decide to go that route.
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Unread postAuthor: mark.f » Thu Oct 18, 2007 6:33 pm

Well, let's hold on a second and think this through a little. You claim to have hit it with a piece of pipe. The surface area of a 4" circle is 4pi square inches. Multiply that by 100 PSI and you get 400pi which is about 1,256 pounds of force. No offense as to your build, but I don't think you can apply over half a ton of force with a piece of steel pipe. The reason something like this would break a PVC fitting is because of the shock. PVC is not good at handling impacts. A standard pressure rated threaded adapter and plug would more than hold 100 PSI... unless you hit it with a hammer. :P

If you do wind up building one of these "cannon fittings", (pun fully intended), do be careful. By the way, solving welding a cleanout adapter is a no-go as well for pneumatics. "Cleanout" adapters are sewer and drain fittings. You need to get a pressure rated female adapter and a pressure rated plug. Make sure all your fittings are pressure rated before using them.
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Unread postAuthor: Solar » Thu Oct 18, 2007 6:43 pm

Very BAD idea. DO NOT use test plugs for a launching system. They are called TEST plugs for a reason. Repeated use and they WILL fail. I have many years experience with these devices and once nearly lost my toes to a 150 psi rated test plug. You have no guarantee that you will not accidentally over pressurize the plug and at that point the low rating will bite you. I have seen someone nearly killed by one that wound up three inches in the dirt.
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Unread postAuthor: silverdooty » Thu Oct 18, 2007 7:24 pm

the problem i see with this is when you install the test plug and tighten it down. it will then expand in the pvc fitting. how long before the fitting will wear our from the outward force of the plug? if the fitting kept it's shape forever it would work. eventually stress cracks will form and the integrity of the fitting is gone. once this happens the operator will instinctively tighten the test plug more. human nature. the fitting will fail before the test plug.

as long as the force required to launch the projectile is less than force required to hold the plug, the plug will not fail. if it takes 100 psi to move the projectile and the plug is rated to 150 psi the plug will not fail. call it one big bassackwards pop-off valve. over time the fitting/test plug connection will fail and you will have a stuck projectile and the plug will go the wrong direction.

continuous inspection of the pvc fitting is a must for this to be safe. maybe a coupling over the fitting would help longevity?
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Unread postAuthor: EGOed » Thu Oct 18, 2007 8:33 pm

Well , you will have 2 walls of pvc , TEE/ pipe ,so I dont forsee a problem with the plug exherting enough force to to break the PVC....The projectile is no Where near as tight a fit as a test plug thefore the test plug would stay in place ....The pressure drop in the barrel takes place in miliseconds as the projectile moves up the barrel , therefore no where near enough force to push the test plug out before the projectile. ...I agree hitting the plug with the pipe is not as powerfull a force as pneumatics , but you cant underestimate the force of mechanical clamping pressure .... A hand vise is capable of creating over 3000psi of clamping pressure.....Im not saying a test plug is a vise but I am pretty confident it will work extremely well for what I want to use it for......You never know till you try. Thanks for all the input guys and I will let you know how it works ...Hopefully soon I can get some pics posted of all my artillary cannons , Explosives mines , mortars , suicide bomber vests , and all the other props I have built for my paintball field using info from this site.....Thanks again
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Unread postAuthor: benstern » Thu Oct 18, 2007 9:20 pm

hmmm this gives me a great idea for a valve.
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