Actually, the tubes generally fail well before the accumulator. If he was popping tubes, it is a pretty good sign that his pressure may have been too high. The accumulator failures are loud and scary, though. Cheers,
Your problem here is not from bearing impact. Not sure what type of plastic you used here but if it was a type used for drain pipe then you have a type of pipe that is not meant to be pressurized. The constant expansion and contraction of the plastic weakens the pipe. You are very very lucky here. I suggest you use brass or copper. You used a material that is not designed to be pressurized. Hope this helps and research your material closely especially anything that will be pressurized.
Looks from the pictures that the pvc was schedule 40. 20 is far far too thin... It looks like eggshells to me Problem is, now he has pvc components, and to shift to partial abs will probably cause glueing/bonding issues. He can probably remove and clean up the caps, and replace the elbow and T pictured and be back on the water fairly soon... Recreating the pvc components in abs will probably sideline him for some time, unless he has a machinist friend, or a stack of tools in his garage My guess is that liquid Co2 was getting into the system, and that's the culprit. The clippard regulator doesn't seem to be able to vent fast enough in this instance. So, the hoses pop. I'd double check to see if there is an anti siphon tube, and the angle of the bottle to rule this out. Mike
No, Safety first, sitting out a battle cause its taking time to make your ship safe is worth it in the long run.
Don't, and I mean *Don't* bust my chops on safety for suggestions on what appears to be common big gun practice. There are how many of these systems in operation? Are you suggesting that the *entirety* of big gun groups stop using their cannon? Ain't gonna happen. Tell ya what, you can re-machine my cannons accumulators for me if you'd like So, after ruling out any problems that lead to overpressuring, refitting the existing parts is from what I can tell the usual course of action. Nothing says he can't take additional measures after that. One of the best accumulator safety things I've seen is mounting it using the next size over to hold and contain the accumulator, while also armoring it against anything that might get past blast shields. Adding duct tape introduces glue to the accumulator... and thus a potential chemical change and degradation. John's idea is far better. Mike
Don't forget to consider what would happen if a copper accumulator fails under pressure. Keep in mind, I have occasionally heard the original builder of this ship say "that's odd, why did that air line burst? It was rated for 600 PSI." It is entirely possible that liquid CO2 got past the regulators and into your main air system. And if liquid CO2 gets into a copper accumulator, that's bad news. Not to mention the difficulties of sealing a metal-to-plastic bond like that. I seem to remember, when visiting the hardware store, that non-pressure-holding drainage pipes are made from ABS, while pressure-holding pipes are made from PVC. That's why I'm hesitant about using ABS. Can anybody confirm or disprove this?
Copper doesn’t shrapnel it splits if it fails. And I believe from what was said earlier it is meant for liquid pressure not gas.
"liquid pressure versus gas pressure"... pressure is pressure as far as the tubes are concerned in steady state. There are some differences in the dynamic effects and stored energy.... Liquids, such as water, can waterhammer and shock incredibly hard in the wrong circumstances briefly, sometimes popping joints, and will transmit a shock through the system. Gasses, will tend to absorb shocks but contain a great deal more stored energy to be released if there is a catastrophic failure(unless your liquid boils when the pressure drops due to a failure, then all bets are off)
I agree with archer on the pressure is pressure thing. The only effect of liquid pressure vs gas pressure, as far as I can figure, is what happens when it fails. When a cannon with a copper accumulator fails, it's almost never the copper itself that fails. I do not know of a single instance of a copper accumulator rupturing copper. What does fail are the ends. Either the endcap or the buna-ball valve detaches from the rest of the system and goes shooting off in one direction, similar to what happens when the valve unscrews from a CO2 bottle. Not as powerful, but it still sends a heavy object flying off at very high velocity. For that reason, some people consider the bursting of a PVC accumulator a safety feature. Other people say that the copper accumulators with a lower chance of bursting are a safety feature. I can see how it might go either way. In terms of moving on and getting the boat operating again, the buna-ball valve and magazines are still intact. Since it is very difficult to seal a joint between a copper accumulator and a PVC valve, I suggest simply replacing the PVC accumulator and using a secondary regulator to bring the pressure down will be by far the simplest thing to do. And double-check that both your primary and secondary regulators are working.
When the CO2 system is pressurized, always wear eye protection (regardless of format). So the accumulator in question is using SCH40 PVC, and contrary to what Carl is saying, SCH40 is too THICK/rigid. It's not as easy to safely contain the pieces when is ruptures, since they are thicker and have more mass, they are harder to stop. It will also fail at a higher pressure than the Class200 pipe used in most of the accumulators. Class200 pipe also makes smaller, and easier to contain pieces within the hull, should something go awry. Class200 makes for a much more predictable/safe failure when that occurs. Using thicker pipe may seem like a good idea, but much more effort has to go into safely containing larger mass fragments. Class200 pipe when it goes, doesn't take much to contain it. The pieces are smaller, and don't have enough mass to go very far. I've not seen much Class200 escape the balsa hull, but have seen Sch40 make it onto another ship's deck. It sounds like this overall CO2 system throughout the ship has some design issues, like only having the one regulator from the desciption so far? It is normally required that the ship have secondary regulators to be able to regulate the guns for penetration testing. If there is not a secondary regulator, there's two issues. One as you saw here, a Williams Regulator failure (such as it getting frozen from a gas leak) can overpressurize the whole system and cause unpredictable failures. The second thing is that your club's Safety and Technical officers will likely take you to task (and not certify the ship for operation) if you can't adjust the cannons for the penetration testing. Where was the fitting going into the accumulator? I didn't see it on the endcap, which leads me to believe it was actually put in the weaker walls? The secondary regulators we use from Clippard have a max PSI of 100, and during catastrophic failure, will instead vent to atmosphere rather than into the CO2 systems. Not picking on you, but to make it clear for others that are reading this, that ship would NOT have passed certification in the NTXBG for safety reasons. For the discussions of copper regulators, that works fine and safely for Arizona Cannon and derivatives as well as std interrupter guns, but as Carl touched on, would likely be dangerous trying to meld onto an existing JC White or Indiana style cannon. The failure point now is the copper to PVC junction. How will that fail? When that fails now you have a accumulator sized copper projectile with a fair amount of speed and mass. Better to stick to PVC where the failure point is known, and can be contained. Again, Class200 is preferred since it fails relatively safely.
... Eye protection should be worn whenever you're working with a "charged" gas system, period! Even if you "think" that the magazines are empty, there can be 1 left "in the chamber". Also, a hose that breaks or pops off a barb can create a whip-like effect at the end, & things like that just somehow have a way of finding an eye. Treat any armed warship the same way you'd treat a firearm (assuming that you've had firearms training, which everybody should have, regardless of whether they own or handle firearms, or even "approve" of their use/ownership by civilians). That is, always treat it like it's a loaded weapon & don't point it at anything/anybody that you don't intend to shoot. Observe safe handling practices at all times, even (especially?) outside of combat events. JM
The mode of failure for both plastic and metal tubing/pipe can still be catostrophic. The key is the intended service pressure versus the pressure to which the pipe is being subjected. Because the ratings on similarly-sized PVC pipe versus copper (or even aluminum) pipe is significantly lower, we are more likely to see catostrophic failure of PVC. Working on the design of compressed gas delivery systems, the cardinal rule/company policy is that we never use PVC on anything intended to hold pressurized gas nor any application that sees variations in pressure over 10psi under normal service. I'm not going to tell anybody that they shouldn't/can't use PVC for accumulators; however, I would strongly advise that they be regularly replaced and not treated as an install-once/permanent component of a ship's systems in addition to going with a thickness rated for a service pressure at least three times greater than the intended operating pressure.
Outlawing pvc pipe I really think is a good Idea. I remember in IRCWCC when we had a tank explode (freon days) because the gentleman had a butt welded steel tank. (it was in the trunk of his car and it was very sunny) After that only sleeved joints were allowed (copper piping) on homemade tanks. Because it was a safety issue! At the NATS event this year I saw several people with these tanks. My thought was then and still today it's not safe. New pvc tanks can fail regardless who built them. I use to do testing of cast piping for naval ships. We were required to test every piece at very high pressure beyond the normal use limit, most passed. The ones that failed normally was just minor leaks in the casting. The others I'm glad we had the BOX. SAFTEY FIRST!! Fun second. I just don't understand some when they think that one or two failures a year are acceptable.
we were still using the other propellent then (freon). with co2 only after the regulator can we use homemade expansion tanks (mostly copper pipe) Danny
This is Big Gun, with fewer balls in the air at much lower velocities. Reload counters at minimum are 2 seconds between shots. Normal reload for a BB is 8 seconds between shots. Hard to hit the same spot twice, like with Small/Fast Gun where there's a hailstorm of rounds hitting close to the same spot. Normally the PVC we are talking about failing is Class200, and this is on purpose. It's easy to safely contain, and it fails EARLY. If it failed late, then it'd be an unsafe big boom which is what was pictured early in the thread because SCH40 was used, as well as it had a fill line drilled into the side which caused a weak point and contributed to the later recipe for failure. Luckily nobody was hurt. This cannon is not indicative of Big Gun style cannons though, and would not have been certified for operation in the NTXBG. This is the first non-combat issue I've seen, and it's due to the particular design failure (hopefully) unique to this one cannon. If there are others like this with the fill line through the side, please rebuild them with the fill line in the end cap where it belongs. I can only patrol my waters around my own club so the other SO and TO's need to check for things like that before certifying ships. Cheers Jeff
Im in the middle of rebuilding my cannon now. I completely stripped out all the old plumming yesterday and reinstalled it as well. I must say though that i had made a HORRIBLE mistake when i had hooked up my airlines for use. The boat is running clippard regulators, but i somehow in the mess of plumming in there by-passed the clippard regulator on the tandum bow guns. This indeed was the main reason for failure and completely my fault. Ive now taken out the torpedo system which has made it much less cluttered and have all the plumming set in place WITH lines running THROUGH my clippard regs. I feel alot more comfortable now with all the knowledge gained, and have a greater respect for the power these guns can make.
Well I’m glade you found the problem. I for one removed all my PVC what ever the reason for failure it isn’t a good enough one for me to lose any flesh over but it certainly opened a lot of eyes. Good luck with your new plumbing and thank you for the knowledge of a potential problem. I was glad to learn from your mistake and not mine but I’m sure I will return the favor before I’m done if I havent already []
