Whats wrong with ABS?

[mrmagoo]

OK its not really a spud gun, but the project im working on is relying on alot of the same princibles. I think ive read somewhere before that ABS is bad for pneumatic spud guns. Why is that? And if the co2 flowing through the system is never stoped and pressurized, would ABS still be a problem?

[thespeedycicada]

abs is very dangerous because most of it is not pressure rated and is cell core i still wouldt use it even if the co2 was not pressurized the cold would shurley make it crack.

[mrmagoo]

PVC will suitable to the cold of CO2 though correct?

[Fnord]

If you are just using it to channel gaseous co2 somewhere and there is nothing restricting the flow, you should be ok. Abs is fairly resistant to cracking even at low temperature, but use metal if you are worried.

Can you be a little more specific on what you are making? We would be able to give you definite answers then.

Edit: PVC becomes brittle in low temperatures. It will be fine if there is no pressure involved.

[DYI]

ABS is usually solid wall where I live, with little to no cellular core available. For pressurised gas systems, pressure rated PVC is considered unsafe, while pressure rated ABS is allowed. Please refrain from comparing pressure rated PVC to DWV ABS. For this application, ABS would be better than PVC because of its greater range of working temperatures.

Any idea where all these myths about ABS pipe came from?

[homedepotpro]

Any idea where all these myths about ABS pipe came from?

yes the fact that all the ABS sold at home depot, lowes and ace hardware is cellular core ABS. If you don't check it before you use it, you might have a gun built from laminated foam.

[noname]

DYI doesn't live in the US (Canada, right?) and apparently, cell core ABS isn't available there. I've seen no solid wall ABS in the Bay Area, but I've seen nothing but solid wall PVC.

[psycix]

ABS has only 2 things above PVC:
-when exploding it cracks instead of shattering
-chemical resistant (pvc may be "eaten" by various fuels)

But PVC is stronger and should be used when possible.

[jimmy101]

... if the co2 flowing through the system is never stoped and pressurized, would ABS still be a problem?

Actually, in terms of temperature affects, this is the worst possible scenario. The CO2 cools as it expands out of the tank. In a continously flowing system you have a steady stream of cold CO2 passing through the pipe. If the the flow of CO2 is used to pressurize a secondary tank then at least you have the flow starting and stopping and you have much more time for the cold to dissipate.

As a rough rule of thumb I would say that any plastic pipe (PVC, ABS, CPVC...) that gets cold enough to frost over is too cold to hold significant pressure.

If the CO2 is flowing through the system, and the pipe is frosting over, but the system is never subjected to more than a few tens of PSI then I would think everything is fine.

[DYI]

Cellular core ABS does exist around here, it is just very difficult to find. Due to the colder temperatures, there is very little in the way of PVC pipe (although I once saw a stick of pressure rated 1" PVC).

[Cappy333]

Has anyone found a USA supplier of pressure-rated ABS? The only stuff I can find is from UK or Austrailia. I don't want to pay ridiculous shipping and VAT taxes if I can help it.

Also, in your opinion what is the maximum reasonably safe pressure for 1.5" sch 40 PVC rated for 330 psi, with a 150 psi rated sprinkler valve.

[Spudnik Tweaker]

I have a question for fellow Americans, reguarding the black ABS pipes sold at Home Depot:

Would they be safe to use as a pressure chamber?

The maximum PSI that I need them to be able to handle is 80 at the most.

Thanks in advance.

[Pete Zaria]

I have a question for fellow Americans, reguarding the black ABS pipes sold at Home Depot:

Would they be safe to use as a pressure chamber?

The maximum PSI that I need them to be able to handle is 80 at the most.

Thanks in advance.

Long answer:
Home depot sells cellular core DWV ABS pipe, which is fine for combustion guns, but is not recommended for pneumatics. I've pressure tested it upto 125psi (as high as my compressor goes) and it didn't blow, but that DOES NOT mean it's safe to use for a pressure vessel for a pneumatic.
I personally would feel comfortable using it at around 60psi, but much higher than that and I'd start to worry about the repeated pressure cycles weakening the pipe.
If ABS does fail, it usually fails very cleanly ("rips" down the side of the pipe and depressurizes rather than cracking and throwing shrapnel like PVC tends to do). The bad news is, it's not made to hold pressure in the first place, and putting pressure in it for prolonged periods of time is asking for trouble.

Short answer: Probably ok upto 60psi or so but going over that is a bad idea. Fine for combustion guns though.

Peace,
Pete Zaria.

[williamfeldmann]

@Cappy

The max pressure is limited by the weakest point, in your case your valve or bike pump (lets be honest, pumping sucks when you get above 100ish). Use plenty of glue and you will be fine @150 psi

@Spudnik

If we are talking about the same stuff, I would be leery of using that in a pressure system, it seems awfully thin walled compared to the sch 40 PVC next to it. I can't remember seeing a pressure rating on it, there might be. If there is a rating on it, I would make a point of calling into the store during the day when the old guys who were plumbers for years are working in the plumbing dept. and ask them their opinion on it's pressure rating. Don't ask the 17 year old who stocks shelves at night, generally speaking they don't know crap and won't admit it. I have used the ABS that you can get at Lowes that i think is the same stuff for a barrel on a simple combustion cannon with no problem.

[Spudnik Tweaker]

I have a question for fellow Americans, reguarding the black ABS pipes sold at Home Depot:

Would they be safe to use as a pressure chamber?

The maximum PSI that I need them to be able to handle is 80 at the most.

Thanks in advance.

Long answer:
Home depot sells cellular core DWV ABS pipe, which is fine for combustion guns, but is not recommended for pneumatics. I've pressure tested it upto 125psi (as high as my compressor goes) and it didn't blow, but that DOES NOT mean it's safe to use for a pressure vessel for a pneumatic.
I personally would feel comfortable using it at around 60psi, but much higher than that and I'd start to worry about the repeated pressure cycles weakening the pipe.
If ABS does fail, it usually fails very cleanly ("rips" down the side of the pipe and depressurizes rather than cracking and throwing shrapnel like PVC tends to do). The bad news is, it's not made to hold pressure in the first place, and putting pressure in it for prolonged periods of time is asking for trouble.

Short answer: Probably ok upto 60psi or so but going over that is a bad idea. Fine for combustion guns though.

Peace,
Pete Zaria.

Thanks for the FYI. You saved me a lot of trouble with that info.

Looks like I will be searching for metal piping instead. My only reason for looking into ABS in the first place was to avoid PVC (I totally do not like the idea of knowing that it can shatter!).