Discussion in 'Weapons & Pneumatics' started by Selley, Aug 7, 2019.
I have already started to create my guns so far they are out of pvc pipe, couplins, and caps
what you are making there is a shrapnel device and an ER trip potentially.
PVC isnt rated for this kind of pressure and doesnt rupture pretty
It sure doesn’t, but protected well it can be fine. I have seen big gun ships last many years without failure from pvc accumulators.
you argue to no end about amperage ratings for wiring and speed controls, but you don't have a problem with a pneumatic pipe bomb?
if only i can throw the pipe bomb at ships
i am using 40mm pvc pipe with a cap on the end and a cupeling cut in halve on the top, so far the wall of the gun is 8mm in thickness
(so far trial and error)
Any home-made pressure vessel is a potential hazard if built by someone who doesn't know what they are doing. PVC is the most common material for Big Gun cannons, and has been proven successfully over many years of combat.
Sorta like barbettes, ABS might be a better alternative to consider
Just keep in mind that pvc use with compressed gasses is generally prohibited in industry as well as by the governing specifications for pvc fittings due to the way pvc fails. Should you have an accident and lawyers end up involved, the optics from a liability perspective will not be in your favor.
Ahoy Selley, what sort of cannon are you trying to make? That piece is a larger diameter and shorter length than I am used to seeing, so I'm not sure what your cannon is trying to do. I'm also curious if you have access to a 3d printer, because that makes Big Gun cannons much easier to make.
My point is that many spec their ESC too low. PVC is absolutely a massive hazard and I have seen them explode and blow the side of a ship out. However, they are very common and a risk that is generally accepted in big gun. Not saying it is a good solution, just a generally accepted one.
The only one I have seen “go” got shot directly by a 1/4” round because the internal armor wasn’t properly in place. It was a incredible sink though. Understand many people rigidly shield the accumulators with short longitudinal bulkheads. I saw a regulator fail once and blow lines apart without accumulator failure. PVC falls in the category of “just because you can (make it work) doesn’t mean you should”.
sorry i don't have a printer they are too expensive and big
That's a very good reference. Don't forget to take into account the note at the bottom:
Note! The maximum operating pressures derates with temperature. At the maximum operating temperature for PVC - 140oF (60oC) - the strength is derated to approximately 20% of the strength at 73oF (23oC).
So working pressure of a 1" pipe at 100 degrees is 60% of the rating at 73 degrees - 162 psi - very close to our 150 psi operating pressure. CPVC does not derate as badly at temperature.
Often schedule 80 is used as well. That makes it good for several hundred psi at 100°F. However, a lucky shot can always ruin the day by comprising the structural integrity.
https://www.aetnaplastics.com/site_media/media/attachments/aetna_product_aetnaproduct/204/PVC Sch 80 Pipe Dimensions.pdf
I have been making guns out of PVC, ABS and Aluminum for close to 30 years. I am not here to defend their use as I am well aware that PVC is not rated for "Air"; only "liquids". It has been used because it was an easy medium to work with, to make efficient guns. When its says rated for 100psi, etc., that's for a liquid. Yes, Big Gun has been using them fine for years, but most Big Gun clubs only allow 120psi maximum at the guns. For years it was only 100psi. Most of these guns made out of PVC only need to use between 75-80 psi or the guns won't pass the penetration test (can't shoot through 2" of Pink foam). Where Fast gun allows you to use 150psi and I could be wrong, but am unaware of a penetration test for the BB guns to verify if they are shooting to hard. Most Big Gun systems use the Battlers or Strike Models regulator set at 150psi and a secondary regulator to reduce the pressure down to what is needed to pass the gun test. I could never imagine using a full 150psi in a Big Gun system as it would easily shoot through a 1/4" of plywood. The main thing is common sense and being careful. We are all shooting projectiles, be it BB or 1/4" bearing.
And to clarify. In the almost 30 years of doing combat I have had a few PVC tanks fail. None was from an "EXPLOSION" as most feel it might be. All have been from the PVC glue joint giving away and blowing the end cap off. Only other major incident I recall was an Aluminum Clippard tank blowing up when we were using Freon as a propellant. It blew the bottom out of a Jean Bart, which sank in seconds.
You did have a PVC tank explode scaring the S out of us, it was the first event of the 2013 season and it blew the side of your boat out with fragments of the tank scattered on the ground while you were prepping to launch. I would recommend a pressure relieve valve just in case you get large spikes in pressure if you use PVC tanks. A spike in pressure by an old Palmer's regulator is what we concluded cause the failure, other than that i have not heard of other PVC tanks exploding.
How did you determine it was a pressure spike caused by the Palmer?
Well that's great. We hit the new guy so hard with the safety warnings and off-topic discussions that he got scared off. Now I have no idea if he's completely out, or stalled while looking for a better design, or pressing ahead with no idea if his design will even function. I'm sure y'all just wanted to help but I don't think it worked this time.
I would encourage Selley to PM me about his PVC gun so I can help in any way I can. I still build and use PVC guns; SAFELY. I am aware of its shortcomings and wanted to share this information. My intent was not to "discourage", but to help guide a new person in a safe direction. When using PVC you need to think about the pressures you are going to use. What regulator you plan to use. How to protect the ship in case something does happen. PVC can and has been used safely for many years. While there have been failures, NONE HAS EVER INJURED ANYONE; including the embellished incident above. Again, Selley I encourage you to contact me anytime and I will answer any question/help you in any way I can regarding the use of PVC.