Compressor Plumbing

[Bob Johnson2]

I was talking to the engineer that came in at work to figure out our compressed air problems. After adjusting all the high/low pressure settings (4 in line 30hp compressors) he mentioned that if our problems persist that we have to start removing all the 90's we have in the old lines and put in elbows. Seems that all the rules that are used for vacumn also are true for compressed air. He also mentioned that it would be preferable to use copper as opposed to the iron seems when the iron starts to corrode it causes quiet a bit of friction, kind of like the corregated flexible plastic hose I use for the vac.
For some reason this never occured to me, must be getting old.

[Paul Downes]

I assume you are having pressure drop problems. I wonder if your water traps are working properly? If you have water in the line frequently it will rust/clog iron lines after a time. In our auto plant we had a regular particulate filter change schedule to stay ahead of the problem. Air pipe also needs to be sized properly for the length of the run. Everything in our plant was iron. Are the compressors truely in line or do they feed individualy into a plenum? This is more common so that you have a redundant setup so a compressor can be taken off line for maintenance.

[tod evans]

bob, this copper suggestion goes against what i`ve been taught since i was a youngster, and also against what most compressor manufacturers advise. the general rule is that if you need more airflow at a tool you need larger diameter pipe, and black iron or galvinized iron is what`s generally used. i`m sure lots of folks will chime in with suggestions for everything from pvc and copper to plastic waterline but honestly iron pipe is used because it helps condense moisture and is strong, qualities the other alternatives don`t have..it`s your system and you do what you want but the advice you where given goes against what the industry as a whole practices......02 tod

[Barry O'Mahony]

I think copper's fine for smaller shops where the main line is 1" or less. But for something like this, the main line must be alot larger. Soldered copper joints decrease in strength as the pipe diameter increases.

[Dave Richards]

Copper is fine. We have miles of it in the ceilings at work. Diameter varies depending on where in the branch it is. Gas supplies can handle flows of several hundred liters per minute with less than a 2 PSI drop. Static pressure is 54 PSI for O2, 52 PSI for Air, 48 PSI for N2O and around 180 PSI for N which has to be able to run even higher flows without much drop since they run tools like drills and grinders.

The last runs of copper down the walls to the outlets is generally no more than 1/2" and the most of the outlets themselves don't even have a 1/2" opening.

By the way, to prevent scale from forming on the inside of the copper when sweating, it is filled with nitrogen to about 1 PSI which purges the oxygen. It's kind of interesting to see old copper coming out in remodels. It's still shiny on the inside even after more than 30 years. Of course our gases are exceedingly dry which probably helps.

As to diameter of pipe, some of the suction lines are 10 or 12" in diameter. Large diameter copper is available if you want it.

[Bob Johnson2]

Paul, we put in 4 new 30hp's a few months ago to replace some old 75's. Ones a variable speed backed up by 3 that are constant, all do 100lbs, the VS is about 135cfm, the rest are 250cfm each. We've been having episodes where when the VS can't keep up the next 30 that should start up at 95lb's doesn't start for about 20 seconds. By then we've crashed the printing presses. Seems the control valves in the constant output units isn't what it was supposed to be. They fixed those and did some adjusting so the next kicks on in 6 seconds instead of 20. The 3rd and 4th kick in in turn if the pressure doesn't come back up, each 6 seconds apart. Supposed to save big $ in electricity.
We're in the middle of replacing the old iron 2 1/2" pipe with black iron 4", this is what the engineer pointed to when he mentioned that copper would be better, even for the 4".

Tod, I agree with you on the iron pipe. It's what I've always been told and what any of the body shops I worked in had for the condensation reasons you mention. That's why I was suprised by what he said. Think I'll take it with a grain of salt.