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Humanoido
09-23-2011, 01:10 PM
I plan to put some tubes of PVC together with glue and pressurize the system. What kind of average to upper limit air pressure in PSI can it take? Thank you for your reply.

graffix
09-23-2011, 01:28 PM
FYI pressurizing the system with air is not recomended solvents in the air will break down the pvc and it could explode.Water is quite high I think read the glue and down the side of the pvc.

Humanoido
09-23-2011, 01:44 PM
Another search brought up this information.

http://docs.engineeringtoolbox.com/documents/796/pvc-pipes-pressure.png

and this

http://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-d_796.html

but doesn't say how long it takes to break down with air or water.

Leon
09-23-2011, 01:48 PM
Use tubing and couplings designed for high pressures, if you want something reliable.

RDL2004
09-23-2011, 02:12 PM
It's not so much that the PVC deteriorates, but that if the pipe bursts it's a shrapnel hazard.

http://www.osha.gov/dts/hib/hib_data/hib19880520.html

Humanoido
09-23-2011, 02:12 PM
Good advice. It looks like PVC has a habit of making shrapnel when it frequently explodes. Copper pipe ratings and behavior is superior.

http://bbs.homeshopmachinist.net/archive/index.php/t-122.html

http://www.copper.org/applications/plumbing/techref/cth/tables/cth_table3c.html

Spiral_72
09-23-2011, 02:13 PM
I plan to put some tubes of PVC together with glue and pressurize the system. What kind of average to upper limit air pressure in PSI can it take? Thank you for your reply.

My answer would be:
If you want to permanently pipe compressed air in your _______ PVC is not a very good idea. Use a threaded pipe and fitting.

If you have a project in mind, and want to play around with an idea.... PVC seems to be fine for compressed air. Many people have done the same, No, it's not advised, it will never be recommended, but PVC is cheap and perfect for a temporary job. Don't exceed 120psi, it might be a good idea to have a pressure blow off, and USE THE CORRECT SOLVENT for the type of pipe you use.... it's worth the extra trip to the hardware store and follow the assembly directions for cleaning, scuffing, and priming (if applicable)

Edit: Oh, and if you do it, don't buy thin-wall irrigation stuff :) Use Sch40 or Sch80

Loopy Byteloose
09-23-2011, 02:17 PM
Schedule 40 is serious pipe - usually steel pipe. I think that Schedule 80 is more rare. I am surprised to see Schedule 40 PVC.

You might ponder that 50 PSI blown in someone's face from a gas station air hose has been known to permanently remove an eyeball. Just because it is air and from a hose, doesn't make it safe. 120 PSI is even more dangerous. Not to be used carelessly to dust the furniture or the dog.

Taiwan loves its plastic products and uses PVC pipe for water distribution and just about everything, including electrical conduit. It doesn't hold up well. It sags over long runs, the tropical sun rots it. And in colder climates it is useless as water pipe because freezing causes it to split into long splinters - nothing left to patch.

I suspect that most of the PVC pipe you are looking at is NOT SCH 40.

Ttailspin
09-23-2011, 03:08 PM
In my experience, schedule 40 pvc in the shade, fully charged 24 hours a day at 200 psi, will last 12 years plus.
and that is in three 50+ foot sections connected, so figure at least 175 feet of pipe..
Plenty of solvents floating around in that shop, and still no signs of failure...

The side of the pipe should be marked with its max rating, don't use for pressure vessels if not marked.
and dont exceed max by more than times 3, unless of course you are wanting the pipe to fail...:thumb:


-Tommy

localroger
09-23-2011, 03:18 PM
In the US Schedule 40 is the standard for pressurized water distribution; as long as you're not buying drainage pipe. It will be clearly labeled by inkjet printing along the length of the pipe. As mentioned before it's not recommended for air because if it bursts, the stored energy of the compressed air will rip it apart and disperse the shrapnel-like shards with great speed, but if it's properly assembled, kept in the shade, and not subject to impacts and vibration, it will hold 100 PSI for years. I have seen entire shrimp plants plumbed for air entirely in PVC. But you don't want to make an air tank out of the stuff and drop it.

ElectricAye
09-23-2011, 04:32 PM
Another search brought up this information.

http://docs.engineeringtoolbox.com/documents/796/pvc-pipes-pressure.png

....

The dotted lines on that graph appear to apply for whether or not a pipe will pass a specification test. They are NOT meant as a design guide for actually using the pipe.

Also, consider that the dangers of containing air pressure are very different from those of containing water pressure. For most purposes, water is considered incompressible, so you can't really store much energy in it as you pressurize it. By contrast to the "solid steel bar" of water, air is like a spring. You can store lots of energy in a gas as you compress it - and if that energy is released because of a pipe failure, it can turn your pipe into a bomb. As so many people have already pointed out, PVC shatters when it fails. If it fails from fatigue or excess water pressure, it tends to just crack and leak fluid on the floor. But if the pipe fails under air pressure, all that springiness of the air propels those slivers into your face.

I don't know what you're doing, but if you need some serious air pressure, stick with materials designed for that purpose. Hoses and air tanks are not that expensive compared to face transplants.
If you are piping relatively low air pressure but your air supply is capable of delivering high pressure, then be sure to put some kind of relief valve in your pipe system so your low pressure system can't inadvertently build up pressure to explosive levels.


my 0.02 yuans worth.

RDL2004
09-23-2011, 05:08 PM
I remember watching an episode of "This Old House" about 15 or so years ago where they visited a factory that made PVC pipe. They showed a QA technician testing a large piece of pipe to bursting pressure. It was impressive, the pipe swelled up to several times its normal size before it finally popped.

Loopy Byteloose
09-23-2011, 05:16 PM
Tolerance to impact is very poor and such situations should be avoided. I see a lot of busted PVC pipe in and around traffic.

kwinn
09-24-2011, 05:18 PM
An old propane barbecue tank makes a good air tank for a compressor after it has purged.

Leon
09-24-2011, 05:51 PM
I once used an old car wheel and tyre when I needed a source of compressed air for experimenting with some Air Muscle pneumatic actuators.

Phil Pilgrim (PhiPi)
09-24-2011, 06:06 PM
An old propane barbecue tank makes a good air tank for a compressor after it has purged.
Are you sure about that? Propane doesn't cause corrosion like the moisture in air can, so propane tanks are not likely to have have any built-in corrosion resistance. Moreover, their pressure rating is probably much lower than that for a certified air tank, since propane turns to liquid at fairly low pressures.

-Phil

ctwardell
09-24-2011, 06:15 PM
Don't use a propane tank, like Phil said they don't have any corrosion resistant coating on the inside. Small air tanks are inexpensive and it isn't worth risking life and limb to save a few bucks.

C.W.

kwinn
09-24-2011, 06:31 PM
Not sure what the pressure rating is, but I have used one for a small compressor for about 4 years now. The compressor shuts off when the pressure reaches 120PSI. Moisture and condensation can be a problem but by preparing the tank before use those problems can be minimized. To purge any propane fumes from the tank I left it sitting in sunlight for two days with a fish tank air pump blowing air into the tank. To minimize corrosion I poured a small can of epoxy paint into the tank and rolled it around to coat the entire inside surfaces. For purging condensation I added a small valve just below the seat of the tank valve and a plastic tube that reaches to the bottom of the tank. This is opened after every use to remove water and bleed off the air pressure.

localroger
09-24-2011, 11:31 PM
Propane tanks are tested to 250 PSI, so they are theoretically safe for normal compressed air use. The corrosion and condensation issues do need to be addressed, as kwinn did.

W9GFO
09-24-2011, 11:49 PM
Air tanks are pretty cheap. I wouldn't bother with a propane tank.

http://www.harborfreight.com/catalogsearch/result?q=air+tank

Peter KG6LSE
09-25-2011, 12:01 AM
LPG is rated at a WORKING pressure of 250 .Look at the neck of one ...
Burst is 3.5 X that . 800 - 900 psI .

I doubt a air tank is rated at that as its not 250 WP but 140 or so ..


I had to hydro test one in my lab in LA . It was used for small rocket for a fuel tank . .(450Lb thrust small ) :)
It poped its top at 1100 or so ..


peter

kwinn
09-25-2011, 06:39 AM
Air tanks are pretty cheap. I wouldn't bother with a propane tank.

http://www.harborfreight.com/catalogsearch/result?q=air+tank

After looking at the price of these tanks I have to agree they may be the better choice. I used the propane tank because the new barbecue had a different fitting and the cheapest air tank I could find was over $100.00. Even the can of epoxy paint cost nearly as much as the air tanks do.

idbruce
09-26-2011, 04:53 AM
Humanoido

There are different kinds of SCH40 pvc pipe, electrical, waste water(DWV), pressure pipe, and perhaps several others. If you are going to use this pipe for compressed air, it should be marked "Pressure Pipe" and have a PSI rating. With my own two eyes, I have seen well constructed SCH40 PVC air systems that were leak proof @120 - 140PSI. I would trust it up to those pressures, provided the pipe has at least that pressure rating printed on it.

Bruce

EDIT: I just read RDL2004's OSHA post, so I now retract :)

Mark_T
09-26-2011, 07:45 PM
Not sure what the pressure rating is, but I have used one for a small compressor for about 4 years now. The compressor shuts off when the pressure reaches 120PSI. Moisture and condensation can be a problem but by preparing the tank before use those problems can be minimized. To purge any propane fumes from the tank I left it sitting in sunlight for two days with a fish tank air pump blowing air into the tank. To minimize corrosion I poured a small can of epoxy paint into the tank and rolled it around to coat the entire inside surfaces. For purging condensation I added a small valve just below the seat of the tank valve and a plastic tube that reaches to the bottom of the tank. This is opened after every use to remove water and bleed off the air pressure.

Purging explosive vapours from a pressure vessel with air? That's incredibly dangerous. Use warm water with detergent.

kwinn
09-27-2011, 01:18 AM
Purging explosive vapours from a pressure vessel with air? That's incredibly dangerous. Use warm water with detergent.

I guess I should have provided a bit more detail on the purging. The first step was to fill it with warm water and dish washing detergent to remove any grease or oil that might have prevented the epoxy paint adhering to the inner surface. After letting that sit overnight I emptied the tank and flushed it with water for about half an hour. Then I emptied the water out, placed the tubing from the air pump into the tank and left it in the sun for two days. At that point I was pretty sure there was very little if any grease, moisture, or propane fumes in the tank so I poured in the epoxy paint, rolled the tank around, and left it overnight to cure.