Sorry you don't understand the difference. Check with someone who tests pressure vessels, maybe they can give you a demo or have a video etc.

I have seen both steel and plastic vessels and tubing rupture both from air and water, there is a world of difference.

Just dont use PVC for air, it is both illegal and dangerous.

I go in a shop with a PVC airline extension several times a year and I have told the owner about it. Funny thing is it did explode a few years ago but nobody was in the shop at the time (time bomb). They repaired the ruptured section with more PVC... tick tock tick tock...

 

Let me take a swing at explaining this:

Air PSI is different from liquid PSI because air is compressible and liquid is not.

You must compress air to raise the PSI. It takes energy to compress air. All this stored energy gets released when the containing vessel is compromised. The stored energy is converted to explosions, heat, noise, etc. Just look at an impact wrench. Releasing air pressure through the wrench performs considerable work in removing lugnuts or whatever.

Water cannot be compressed. If you apply a force to a portion of liquid within a closed hydraulic vessel, the PSI rises extremely rapidly, with no energy being stored. Compromise the vessel, and the pressure drops, perhaps rapidly, but there is no significant stored energy to wreak havoc.

Imagine the following: start with a big old truck tire at atmospheric pressure. Attach an old fashioned manual tire pump. Pump away. How long is it going to take you to raise the pressure to 30 PSI? It takes a long time and you will get really tired. Your sweat and effort represents the work done to raise the pressure, and thus the stored energy. That same energy, released suddenly, can blow the rim off a split-rim wheel and kill you, which is why truck tires are supposed to be filled in a safety cage.

In contrast, connect a grease gun to a hydraulic tank filled with water or oil. With one pump of the handle you can bring it from 15 PSI to 5000 PSI. How much energy did you put into the system (Answer: not much). Now crack the outlet valve on the tank. How much energy gets released? Answer: not much, because no energy was put in. Nobody worries about a bearing blowing out and killing you with a wad of grease, despite the fact that it is at "5000 PSI".

 

well said fefarms.

 

Read this link from the OSHA page....

http://www.osha-slc.gov/dts/hib/hib_...b19880520.html


Here's a teaser...

May 20, 1988

MEMORANDUM FOR REGIONAL ADMINISTRATORS

THRU: LEO CAREY
Director
Office of Field Programs

FROM: EDWARD BAIER
Director
Directorate of Technical Support

SUBJECT: Safety Hazard Information Bulletin on
the Use of Polyvinyl Chloride (PVC) Pipe
in Above ground Installations


The Dallas Regional Office has brought to our attention a potential serious hazard existing with the use of polyvinyl chloride (PVC) plastic pipes for transporting compressed gases in above ground installations. An employee in a Texas plant was injured recently by a rupture in a PVC compressed air line. Plastic projectiles from the point of rupture caused lacerations of the employee's hand. This is noteworthy because the Plastic Pipe Institute, in its Recommendation B dated January 19, 1972, recommends against the use of thermoplastic pipe to transport compressed air or other compressed gases in exposed plant piping. (See attachment.)

Furthermore, sections 842.32, 842.43 and 849.52(b) of the American National Standards Institute/American Society of Mechanical Engineers (ANSI/ASME) B31.8-1986, Gas Transmission and Distribution Piping Systems Standard, limit the operating pressure of plastic piping distribution systems to 100 pounds per inch (psi) and prohibit the installation of such systems above ground except where ". . . the above ground portion of the plastic service line is completely enclosed in a conduit or casing of sufficient strength to provide protection from external damage and deterioration." (Excerpts attached.)

Additional consensus standards applicable to PVC compressed gas systems include American Society for Testing Materials (ASTM) D1785-86, Standard Specification for Polyvinyl Chloride Plastic Pipe, Schedules 40, 80, and 120, and ASTM D2513-86a, Standard Specification for Thermoplastic Gas Pressure Piping Systems.

Please disseminate this bulletin to all Area Offices, State Plan States and Consultation Projects.

 

Oldcoupe42, I think that it is great that you asked a question on this board, got an answer, and learned something and plan to use that info to make your life safer. It would be horrible to hurt yourself or someone else. You would most likely be in the garage when the explosion occured, as it probably would occur during pressure swings caused by you using the air. It should not be the lwasuits that should worry you but the fact that someone could get seriously maimed. Try cutting pvc with a regular blade on a chop saw, like some people do, and you will see how it behaves differently under stress than metal does. I was at a diving outing where a man got his thumb blown off from an explosion at the scuba tank filling staion. It would have been fatal to a lot of people if there had been anything that when exploded would fracture and produce shrapnel.
Again, thanks for asking the question and listening to peoples' advice.

P.S. anyone remember the old steam systems? Other than a boiler exploding the greatest danger would be a pinhole leak that would have a highly pressurized jet of steam escaping and that could cut right through the body. However, the pipes would never explode and produce shrapnel, they would burst in an isolated area instead.
Good luck with your plumber/neighbor, I hope you hook him up decently for helping with your airlines. Maybe you could run an air hookup to your property line that he could link into if he needed to!

 

Wow, you learn something every day!

Before plumbing my detached garage with airlines, I read a couple of articles on plumbing compressed air systems - one from a car magazine (the name of which shall be withheld to protect the guilty) and another I think I pulled from the internet.

Neither article recommended using PVC, but neither one explained why, and my conclusion from the articles was that PVC could contain more contanimants than metal pipe. However, the magazine article showed pictures of the author's plumbed garage using guess what - - - PVC, of course.

Well, I plumbed by garage using PVC - and a darn nice job I did too. I used thick-wall one-inch PVC thats rated at least for 150 psi (I think its rated for 300 psi - you can bet I'll check tonight!), and have really liked the layout of the system and ease of installation - no leaks etc. Until tonight, when I discovered the REAL reason NOT to use PVC in this forum. And I should have known better - I already knew you can't pressure test water or sewer lines with air because the air will compress and distort the results, so you have to fill them with water, then seal them up to pressure test. But the physics of the problem didn't translate into the potential to explode. . . .

This is one of the better examples of how neat this forum is. Will I take out my PVC lines now that I know they're potentially dangerous? Not anytime soon, just cause its a money issue. Will I monitor the line pressure a lot more carefully in the future (I usually run pressures of 50 - 70 psi, and never more than 75 psi through the use of a regulator before the lines) - ABSOLUTELY.
IF I had used the thin-wall cheaper PVC instead - I would take it out right now. I think my system is relatively safe due to it's location (in the attic except for drops) but primarily because the only real work I run off the PVC lines is low-pressure brad nailers and/or nozzles to blow the dirt out. The real work I tend to do outside the shop using nylon air hoses that bypass the pvc system. But I'm sure glad I read this forum thread - even though it not what I wanted to hear!
Sometimes I don't wear seatbelts either! Living dangerously in Colorado

 

Good luck with the re-fit.

 

Went out to the garage and checked my PVC airlines to see what they were rated - in typical overkill fashion, I used Schedule 40 PVC rated for 480 psi - which probably explains why I haven't had any problems with my system (that and the relatively low pressures I run in it). However, I'm not trying to justify the use of PVC airlines - knowing what I now know, I wouldn't have used them in the first place! Oldcoupe42 - Thanks for asking the question - just too bad I didn't know about this forum when I put the airlines in . . . . .

 

Yep, that is 480PSI liquid pressure, there is no rating for gas pressure.

 

Has anyone on this site used copper pipe for air lines and if so how does is work and what size 1/2 or 3/4? Copper is much easier to work with than iron for me.
Thanks,
Bob

 

I am just like you in that copper is much easier for me to install than iron. I used 1/2" and it works great!!! It's easy to put together and it is safe. A useful tip is once it is put together and before hooking up to your compressor or other equipment, fill the pipe with plain water (no need for pressure) and let it soak for 12 to 24 hours. Then flush with clean water for maybe five minutes, and blow dry with compressed air. This will help remove some of the flux that may collect around the interior of the soldered/brazed joints. This is normally not too big of a problem, but on occasion some of the flux can break loose and travel down the air line getting into your equipment/tools.

pbfoot