How much pressure with large sch80???

jeepkahn · Wed Jun 03, 2009 1:53 pm

Looking to build a LARGE coaxiel using 8" sch80(rated 250psi) for the chamber and 4" sch40(rated 220psi) for the barrel... All fittings will be sch80... I know some people are hesitant to go beyond 150psi regardless of rating on pvc, but do you think 200psi would be safe if all the solvent welds are sound???

And I'm also seriously considering making a cannon with 8" sch80 barrel, and 16" sch 80 chamber depending on responses...

jmeyer1022 · Wed Jun 03, 2009 1:55 pm

What will you shoot good sir?

jeepkahn · Wed Jun 03, 2009 2:05 pm

jmeyer1022 wrote:What will you shoot good sir?

with the 4" barrel, plastic peanut butter jars, cantaloupes, 2litre soda bottles, soft balls, mini basketballs, etc

the 8" barrel, punkins of course, jell-o balloons(w/sabot), larger cantaloupes, footballs, small children(just kidding), etc...

Biopyro · Wed Jun 03, 2009 2:43 pm

I would feel more than happy using it to the rating. That's what it's there for after all!

Carlman · Wed Jun 03, 2009 2:46 pm

I would not go over 150 with any material with failure charactoristics similar to PVC. All it takes is a drop or a knock...

jeepkahn · Wed Jun 03, 2009 3:38 pm

after looking at this http://www.engineeringtoolbox.com/pvc-c ... d_796.html I do feel a little better... prolly a good reference if someone wants to add the link to the wiki....

Carlman · Wed Jun 03, 2009 3:59 pm

Pressure ratings are good and all but, burst pressure changes with age and the way it is handled/looked after...

Technician1002 · Wed Jun 03, 2009 6:30 pm

jeepkahn wrote:after looking at this http://www.engineeringtoolbox.com/pvc-c ... d_796.html I do feel a little better... prolly a good reference if someone wants to add the link to the wiki....

And this one did just the opposite. I wouldn't even consider standing next to an 8 inch at 150 PSI.

[youtube][/youtube]

I don't like the failure mode.

spudtyrrant · Wed Jun 03, 2009 6:43 pm

[youtube][/youtube]
notice where it failed tho, i don't remember who posted it but it is somewhere on this site, he said the solvent weld had only been drying for 20 minutes before he shot it

Technician1002 · Wed Jun 03, 2009 6:53 pm

spudtyrrant wrote: notice where it failed tho, i don't remember who posted it but it is somewhere on this site, he said the solvent weld had only been drying for 20 minutes before he shot it

I don't have video, but I have had PVC fail. My Mouse Musket is retired due to a crack. It would have shattered if it failed at high pressure.

I don't have a quick link to the vid, but one of them is of a kid getting ready to shoot a sprinkler valve on and while setting up the camera, knocks the gun over and it explodes when it fall over. Point being, if and when an 8 inch fails at over 100 PSI, it would be very dangerous to be near. PVC shatters.

jeepkahn · Wed Jun 03, 2009 6:53 pm

And I'm also gonna be using SCH80.... And if i build either of these, they will be remote fill and remote triggered...... Do you think anyone could handle either of these with even 50psi???

Technician1002 · Wed Jun 03, 2009 7:04 pm

jeepkahn wrote:And I'm also gonna be using SCH80.... And if i build either of these, they will be remote fill and remote triggered...... Do you think anyone could handle either of these with even 50psi???

50 PSI, sched 80 should be fine. As the pressure doubles, the energy goes up 4X. My 6 inch Dragon worked fine at 50 PSI. It was sched 80 in the valve area. It is unlikely to explode even if cracked.

The Mouse Musket got a crack when not under pressure and it was discovered while filling it with the new valve piston. It did not explode, but I quit filling it at 50PSI.

The photo is blurred, but the leak was at the muzzle end in the coupler and reducer. If this happened at high pressure, I am sure I would be sweeping the pieces.

Biopyro · Thu Jun 04, 2009 4:51 am

If you wouldn't feel happy using it below the pressure rating at 150psi, then you should still have issues at 100psi. Having done burst tests on bottles, I can tell you that the pressure it bursts at isn't going to make much of a difference if you're holding it, they're all ferocious.

http://www.crazybuilders.com/item.php?i ... ct_section

Have a look at this video, PVC isn't weak stuff!

jeepkahn · Thu Jun 04, 2009 10:24 am

Also as a point of note is that I'm refering to sch80 cpvc which is much more impact resistant, and upon failure doesn't shatter the same as white pvc, and has a much higher working temp rating as well...

I agree with BP, I think it'll be fine to 200psi....

Technician1002 · Thu Jun 04, 2009 11:55 am

Biopyro wrote:If you wouldn't feel happy using it below the pressure rating at 150psi, then you should still have issues at 100psi. Having done burst tests on bottles, I can tell you that the pressure it bursts at isn't going to make much of a difference if you're holding it, they're all ferocious.

http://www.crazybuilders.com/item.php?i ... ct_section

Have a look at this video, PVC isn't weak stuff!

Doubling the pressure increases the stored energy 4X. The reverse is true. At lower pressure the energy required to grenade the plastic container will become too low to do much more than hiss badly. For example given with the soda bottles. Fill a few to 10-20 PSI and stab then with a knife. They generally won't split and turn into shrapnel. The required energy is not there.

The same applies to Sched 80 PVC. It may crack and leak at under 50 PSI, but the force needed to open the crack and propagate it isn't there.

The linked resource is excellent. The points of leak before break and yield before break are good. The unknown is the pressure where a crack propagates into a catastrophic failure.

What is important is PVC has a brittle fracture failure mode. That is of concern for safety.

Crazybuilders has a discussion section on the blast box test. It has more info.
http://www.crazybuilders.com/forum/showthread.php?t=8