Air resovoir tank...PVC?

[Phil Crow]

I'm getting ready to buy an air compressor, one of the 20-gallon, belt-drive type units. I figure this gives me the largest comperssor size I can get in a portable unit. Obivously, more air is better, and if I need more air, the logical solution is a larger air reservoir. My question is this: Since Schedule 40 PVC is rated to ~240 psi and my 'presser only goes to 135, why not use large-diameter (6 or 8 inch) pipe, cap both ends, tap one of them and hang it from the ceiling (connected to the 20-gallon tank with a flexible hose)?

I realize that plastic is not the recommended material for compressed air systems, but that is because hoses, etc attached to small-diameter PVC tend to get pulled too hard and crack the plastic pipe. This is Not A Good Thing. However, with nothing attached to the reservoir that should get pulled on, are there any other potential problems?

Thanks,

-Phil Crow

[Dave Hinz]

I asked this of a plumber friend years ago, and he told me that it would only be a good idea if I was tired of being alive. The repeated cycling of pressure/release are the problem, apparently.

It gets pulled & pushed every time the compressor goes from off to on, and when you use enough that it comes back on. Don't do it.

Dave Hinz

[TeamCasa]

Picture this - Pumpkins getting launched hundreds of feet from an air cannon.

PVC is dangerous for compressed air. Small diameter PCV and other plastics are fine for hoses but when used in 6" or 8" pipe!! That's a tremendous amount of stored energy. Your 20gal tank should be addiquate. If not, many extra storage tanks (steel) are avaliable for little money and IMHO, much safer.

You don't live anywhere near SOCAL do you?

Dave

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[Frank Campbell]

snip Rather than typing it all out this links to a site explaining why a larger tank probably will not accomplish much other than taking longer to fill it:

you do go for a second tank please get a proper metal tank approved for that use.

FrankC

[Bay Area Dave]

NEVER use PVC for any portion of a compressed air system. The plastic can become extremely brittle over time and when it breaks under pressure it produces plenty of shrapnel. Don't do it!

dave

Phil Crow wrote:

[CW]

Should make a pretty good fragmentation grenade.

[Scott Lurndal]

You might have fewer problems with the group denizens if you were to suggest, rather than command.

For what it is worth, metal pipes also produce shrapnel when they burst (a friend still has one black arm from cutting into

6" steel which was undergoing a pressure test at the time).

PVC embrittlement occurs primarily due to UV exposure. For the OP purpose, a containment cage could be easily constructed to contain any shrapnel should the PVC fail. 3/4" CDX should be sufficient.

External physical damage to PVC (when used for the OP purpose of air storage) can be prevented with the same containment cage described above.

The original poster must determine the risks vs. benefits and make his own decision.

scott

[Larry C in Auburn, WA]

Just be sure your widow, er wife, knows where you bought the PVC so she knows who to sue for selling you something not suitable for the task.

[Greg]

This "PVC grenade" stuff seems like a perfect subject for the guys on "mythbusters". They like to try to duplicate these things under controlled circumstances. I have tried to explode PVC pipe with compressed air and couldn't duplicate the "shrapnel" situation. I will still agree a proper tank is a better option, but I would like to see it proved sometime.

[DJ Delorie]

Enough people have had it happen to themselves (based on their personal reports here) that it would be a short show. Here's two for example:

?selm=34174B09.36C%40sprynet.com

[CW]

I can show you a hole in a shop wall.

[Greg]

I see a lot of conjecture and "I new a guy who heard a story about..." anecdotes but no real controlled tests.

I do know that when I intentionally blew up some "baked in the sun" sch200 PVC it was pretty unexciting. The "shrapnel" fluttered about 30' before it landed on the ground. It wasn't even that much of an explosion, more of a "pop-whoosh". (it was somewhere around 500PSI from a CO2 cylinder) Certainly if it was next to your head it might have had some dangerous velocity but it didn't go very far. Most of it stayed with the pipe. This was a very "uncontrolled" test so I don't put it an much more than the anecdotal category.

[CW]

[Bay Area Dave]

PVC gets brittle with age. that's why old PVC is so dangerous in an exposed compressed air system.

dave

Greg wrote:

[Bay Area Dave]

Nothing I could do can squelch the "denizen's" smart assed comments, Scott, yourself included.

I wasn't "commanding". The term "never" is applicable for safety's sake. Since you take exception to my comments, all I can tell you is, TOUGH!!

dave

Scott Lurndal wrote:

[Bay Area Dave]

Just because YOU can't duplicate the conditions leading up to a catastrophic failure doesn't mean it doesn't happen, Greg. You are so clueless! Your prideful attitude prevents you from understanding something that you haven't witnessed with your own eyes.

dave

Greg wrote:

[Greg]

Lighten up boys, I just said I would like to see the guys at mythbusers take a shot at it. If nothing else they would have some nice examples of the terrible things that can happen. I still say that in the grand scheme of things and the real accidents that happen around wood shops I doubt exploding PVC lines would make a bump on the chart. I would worry a lt more about stuff flying off a table saw blade.

[Bay Area Dave]

Now I agree; airborne chunks of wood have gotten me more than once! :) (But then again, my air system is "L" type copper...)

dave

Greg wrote:

[GTO69RA4]

Age, sunlight, oil in the air from the compressor, vibration, and pressure cycles all contribute to the degrading of PVC. It will also weaken in cold temperatures.

I sure don't want it in my shop. Over the past few years most mechanical-related boards I've been on have had multiple first-hand accounts of PVC air systems blowing up. Only one or two related to iron or copper systems I can remember.

GTO(John)

[Dave Hinz]

The original poster was talking about making a tank out of large diameter PVC, not just running lines.