Compressed Air Lines in a Shop
I plan on running some size main line at the ceiling next to the buss-duct and DC piping, the idea being a spine running the length of the building, through a pass-through in the wall between the two rooms, carrying all the mechanicals to make tapping easier in the future.
I've seen references to flow drop in a line of a given size at so many feet, but haven't had any luck finding a chart or design guide. Should it be treated like DC piping and stepped down along the way? I will have minimum main line of 165', with say a 30' average drop to each machine. I also assume that some consideration should be given to installation to allow for draining, i.e. not level. What is an acceptable per foot pitch, or is it not really necessary?
And what are people using for their lines? I'd like to keep it as simple as possible, maybe PVC? Or is that not a good idea?
As to pipe materials, plastic is marginal at best. I know some shops get away with PVC, but I've read a few accounts (and know someone personally who experienced this) of catastrophic failures wherein a pipe fractured and created a chain reaction of shattering plastic that disintegrated large sections of piping before the pressure dissipated. These failures often seem to be kicked off by use of tools that involve impact. In one case I know of, it was a framing nailer being used to build some shop structure. Anyhow, plastic seems to be risky, and often illegal. Heavy copper works in a small shop, DIY situation (I used it) but it's a very expensive material right now. For a shop like yours I think you're looking at iron and the services of a pipe fitter.
The size of the piping depends on the line pressure and the volume of air needed. You should figure out what the highest pressure you'll need is, and the greatest volume you might need when the shop is going gangbusters, and plan the system to deliver that. Pipe sizing is a lot like electrical wire sizing; larger is always better. Since larger piping is more expensive, you'll be tempted to buy smaller piping instead, but this is false economy. If the piping is too small for the demand, then pressure drop becomes a problem. You turn up the pressure to overcome the pressure drop, which means the compressor has to work harder and you pay more for electricity (not to mention compressor maintenance) than you would've paid for bigger piping. If you know your maximum pressure and volume requirements, you can apply Boyle's law and some basic geometry to figure out how fast the air might move through pipes of various diameters. A typical recommendation I found was to engineer the system so that air moves through the pipes at no more than 20 feet per second.
From contributor D:
I have had success letting the main fall with the air flow and putting a drop at the end with a valve to open once in a while to clean out the main. I take all drops (except last one) off the top of the main and run down to a workable height and take off the side of the drop to the machine and continue the drop another foot or so with a drain at the bottom. If I were doing this I would use black iron pipe. Copper is expensive and plastic has some danger with bursting.
From contributor T:
We ran a complete loop using Kaesers smart pipe (I think that's what they call it). It's a blue anodized aluminum pipe that has quick connect/disconnect fittings and is fully tested and designed for use with compressed air. PVC in some states is illegal for use with compressed air in a commercial setting.
We run off of our compressor through our dryer into a 150 gallon tank, then through a gel water/oil filter and out about 75 feet to the start of the loop. It runs around the entire shop with drops where we need them. With the blue pipe you can always move the pipe later if need be without a ton of effort; we've done this two or three times since setting it up.
We have had excellent results. When the valves on the equipment are shut off, we were only losing 40psi at the tank overnight without the compressor running. It's not the cheapest solution, but like so much in manufacturing and life, it's much less than doing it the cheap way and then doing it the better way.
From the original questioner:
Thanks for the input, especially the warnings on PVC. I never thought it was a good idea, but several, albeit non-industry, people had suggested it to me.
Contributor J, I agree that bigger is better and can overcome some shortcomings in design, simply by brute force.
Contributor D, I like your ideas about draining - I'll have to figure that in.
And contributor T, I'm familiar with SmartPipe, but had never heard any real world experience with it. I also know it's pretty expensive, and I have a large system to lay out. That said, I agree with you 110% about it being cheaper to do it right the first time than wrong several times, hence this entire reworking of the infrastructure of the shop. I'm tired of spending huge money on wire, conduit and labor to get something set up, only to have to remove/rework/or recycle it a year later.
It looks like I need to get a price comparison between copper and SmartPipe; I don't think iron is for me.
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