Last saterday during gunnery exercises at the pond i had a expansion tank explosion while gassing up Hindenberg. Luckily for myself i didnt get hit in the face with any shrapnal as i hadnt yet put on my saftey glasses. It flew everywhere! What are your thoughts on what caused this? Im using a BC regulator and have fired the guns before with no problems. It blew as i was putting the superstructure on just a few seconds after gassing her up without any warning.
Probably plastic fatigue or damage from bearing impact. Plastics do have a finite life when subjected to repeated stress changes, such as the sudden drop with a refil after firing. What regulator? the heavy brass one? those can drift over time as they get dirty. What pressure? What was the pressure rating on the part that failed?
Yea the heavier brass one, and im not sure of the pressure rating, i cant find one on there. I didnt build the guns so im not sure how old they are ether, but i am contacting the original owner to find out. But how often do these failures happen? I dont like my ship being blown full of holes while im not battling.
fairly uncommon from what I have heard/seen, however, you need to make certain they are armored from bearing impacts. the heavy brass one will be probably ~150psi or a skosh less, as it is for fast gun. it may be too high a pressure for that setup. go to a hardware store, find the part that failed, and read the max pressure rating on it (if it says)
Wow, that's scary. I'm glad I've never had an accumulator failure on my ships. Anyway, let's try and figure out what happened. First, how thick is the PVC? is it the schedule 40 stuff, or the schedule 80 stuff? One is thicker than the other, and if you've got the thinner stuff then that might explain things. Second, was there any sign of fatigue or damage beforehand, like cracks, dents, etc? Also, were there any unusual sounds, like creaking, hissing, etc immediately before the accumulator failure? It may not be easy to spot under all the superglue, epoxy, and shoe goo, or to hear over the noise of a pond and a powered-up ship, but if there was any indications before the event, it'd help to know what it was. Third, was the PVC exposed to direct sunlight at any time? Direct sunlight damages PVC. I see that some of the PVC is yellowed, does anybody know what that might indicate? Fourth, I don't see any blast shields in the ship. Did it originally come with blast shields, or not? A lack of blast shields, especially before you got the ship, may have resulted in bbs hitting the accumulator. Regardless, it's a good idea to install blast shields. If you ever have another accumulator failure, the blast shields will help contain the blast. Fifth, if possible, you should stick a pressure gauge on the air line to the accumulator, and find out the pressure it's currently at. If there's anything wonky going on with the regulator, or the secondary Clippard regulator, you need to identify it. Also, see if adjusting the dial on the Clippard regulator changes the pressure on the gauge. Sixth, if you trust the other cannon with pressure, hook it up and fire it a few times. See how the temperature is affected when the cannon is first charged up, and also how it is affected after emptying your CO2 bottle. How much of a temperature change is there? Does it feel cold? is it too cold to touch? Does condensation or frost form? Lastly, since the accumulator is currently not attached to the cannon, I am curious about some of the dimensions. Could you please measure the diameter of the buna ball and the air passage?
PVC acculators explode. They don't do it often but I hear of about one explosion a year. It cold be for many reasons but they do fail. I never plan on using them for this reason. I think they are dangerous and an injury waiting to happen. That being said, I'm glad you weren't hurt and I would recommend a metal tank. I make mine out of copper pipe with ends soldered on it.
http://www.pvc4pipes.org/documents/files/PXII/sess5b/Moser.pdf that is very interesting.... see the attached link. please keep in mind that stress in psi is different than the pressure of the internal fluid.
CO2 is prone to absorption in plastics. This may cause problems even when the plastic is operating in its rated range.
Last year I was just cutting a peice of 3 inch white PVC on my bandsaw, and it blew apart in my face, luckly I was wearing my safety glasses. But it was enough to cause cuts on the side of my face and arms. I was quite suprised when it happened, what I think happened was that the bandsaw blade got jammed in the PVC, and instead of the saw stopping, the PVC came apart violently. I would never use it in a pressurized environment for sure after seen that. It was all over the garage, up to 10 ft away.
Hold on, a second. Before we start condemning PVC as a cannon material, we need to determine the cause of the accumulator failure. Did the accumulator fail under normal operating load, or was there a larger-than-normal operating load on the accumulator? That ship (and the cannons in it) have been in service for years, so I have a hard time believing it would randomly fail without a reason.
If it had been in service for years, I would not be at all supprised with a fatigue failure. Just because our pressure pulses are below the rating of the components does not mean that they will not eventually fail due to fatigue. Most materials have a finite life under oscillatory loading, although some do go basically infinite (see steel) others do not (see aluminum) with sufficiently low (but not absurdly low) transient loadings.
Just got an email back from Ken, the original owner and he said he originally operated the cannons around 85-100psi. So aparently i was using to much pressure as i was running the BC reg. striaght to the guns without any other regulator to bring it down from 150psi. I believe that was more than likely the cause of it or the fact that i may have froze the regulator. I did have one hose blow off the first time i aired the system up which may have frozen the regulator. Right after i aired it up and found the leak i turned the air off replaced the hose and then aired it up again where i was greeted with a nice explosion. This may have been the cause seeing as a few days before the guns worked fine. But the high pressure does scare me so should i opt. to drop the BC reg and put in a paintball type reg and a gauge? Or should i just add clippard regulators? Im more accustom to the paintball type since i have a paintball background. But which do you guys find to work better? And how do you install a gauge if i were to use clippard regs? The PVC itself looked fine, like i said before they worked fine days prior to the explosion and i havent battled the ship so unless it had past damage which wasnt visable i dont know. Im not sure what kind of PVC it is as i cant find any markings or ratings on them, but maybe ill give them a closer look later. But what kind of PVC should i look at buying to fix her up? Im really new so im trying to do it right this time to try and avoid this happening again. thanks
Don't use PVC, as you found out it has a tendency to be dangerous when it fails. Try using ABS if you want to stay with plastic. ABS doesn't shatter when it fails so it doesn't produce frag.
I would always suggest wrapping Duct Tape around any PVC you are using if it is going to be pressurized at all... we always put on at least 2 layers over our spud cannons... and for good reason too, PVC is quite dangerous... ABS is alot safer to work with.
In many circles, the relative;y low failure pressure of PVC is considered a safety valve - it prevents higher pressure from building up. However, they should always be operated sith a secondary regulator (which I think I see in the picture) that lowers the pressure to 85-100PSI so you can adjust your gun's power. There is a diagram on safe, effective CO2 use on the NTXBG.ORG web site. Also, you should NEVER turn on your gas before you put on your safety glasses. You should also not arm your system until you are in a designated test firing area or are on the pond. You should be able to reach your gas safety (arming) switch (valve) from outside the ship, of course. Further, it is our custom (and, I believe, rule)in our club to announce when a ship goes "hot." It is a really bad idea to carry a hot ship around or to go hot in the pits. Cheers, Wreno
PVC does fail and is dangerous. Yes there may be other reasons why it failed but the end result is the same. No one here is condeming pvc for your use but I read one explosion a year. That's one too many in my book and constitutes an unsafe material. I also agree that there should have been no gas up w/o safety glasses or in the pits but I'm not going to lie to you and tell you I have always been safe with my co2. I really like the idea of wrapping the pvc with duct tape and I have to say that is one of the smartest things I have heard. Either way, it is allowed and I hope no one ever gets really hurt off of it. Be Careful!!
Well im just glad that no one else was around. I had pulled my truck right up beside the pond and was going to gas up before adding the super to put it in the water. Next time ill deffinately have some eye protection. Looks like ill be making the switch over to ABS.
PVC pipe (SCH 40) and its fittings are not rated for gas, only liquids and could fracture and fail, IE the photos Carl
I can't remember why, but I was looking around at a number of plastic mfgers' web sites a couple of years ago. There was a common message on most, if not all: NEVER USE PVC FOR A PRESSURIZED GAS CONTAINER. I was definitely struck by the consistency of this message, from multiple industry sources. If the plastics industry itself "condemns" PVC for use in pressure vessels, who are we to think we know better? That said, I've got lots of PVC accumulators myself, & I've managed to shatter 2 or 3 of them. I wrap all of mine with tool drawer liner, held together with zip ties. It doubles as impact protection & scatter shield. JM
