View Full Version : Shop Air Question?

06-19-2009, 11:44 PM
Recently I installed a 10 Horsepower Champion Air Compressor. Also lots of blacl line and a air drtyer and also a Nitrogen membrane system. Now the air compressor (no NOT buying another one) had to be cranked up to 150 pound output. The next time I look at it (the air pressure gauge) its reading 175 pounds pressure? I think this is way too high. What should a shop air system be set at if you have a couple of tire mounting machines and also 4 hose reels for air tools and such? Is 150 pounds asafe and OK to run?? All pipes are 1.25 diameter black pipe. Thanx Mike

06-19-2009, 11:47 PM
175 PSI is what you want from a real machine.

I say your pipes are good to go. dont change a thing yet.

06-20-2009, 12:03 AM
Put a regulator at the compressor, or at each station where you are using a tool/equipment and adjust the pressure to meet the requirements of the tool/equipment you are using.

That way, you won't blow a tool up by exceeding the specs.

Someone else pipe up, if they think this is wrong.

06-20-2009, 12:55 AM
I believe most air tools are designed to run at 90- 100 psi..at least that is what the instruction booklets that come with the air tools say. When I worked in a commercial tire shop we ran 150 psi in the shop lines..the air tools might not have lasted as long as they should but we needed to get the job done.

Now that I run my own shop I run 100 psi in my air lines. I've found that bigger air hoses..1/2" with 3/4" iron pipe trunk lines will sufficiently power most air tools.

06-20-2009, 01:24 AM
I gotta ask about the nitrogen membrane system. Obviously for filling tires, yes? My personal opinion is that these systems are just to sell something that is not really needed to a ignorant customer. I can see that dry air with no moisture is good for filling tires, but nitrogen? Air is already 78%. Do you believe nitrogen for tires is really that much better, or are you charging customers for it, or do you just have it to appear competitive with the other tire shops that offer it? I see cars with the green valve stem caps and I think, "You got taken by a scam!" Perhaps I am wrong, If so, is there any scientific proof that nitrogen in tires is worth the extra $ that tire places charge?

Jim Shaper
06-20-2009, 02:25 AM
Doozer, nitrogen doesn't expand as much as regular "air" when heated. I can point you to several racers who can get far better consistency on their laps (road courses) running nitrogen and all of them will swear by it.

Now for a street car? Pffttt.... Who's going to notice an increase of a few psi when their tires heat up?

06-20-2009, 03:43 AM
Your compressor, probably a two stage or rotary, is clearly capable of 175 psi. Most of your tools will probably be happy with much less. Drop the pressure and you'll maybe save some energy cost and also have a safer situation if someone puts full pressure air into a blow gun, tool, etc.

Drop it too far and you may not have enough air for simultaneous users. You'll have to find the sweet spot between maybe 125 and 175 psi at the tank cutout. Note that storing the air at 175 psi, even if you draw it off at 125 psi or so, gives you more effective capacity before the compressor kicks back on. BUT, you paid a slight penalty in energy cost along the way.

As noted above, put filters and regulators at each station.

As for the safety of 175 psi, there have been a few cases of poorly cast import fittings not handling the pressure. Pipe it up with good quality connections throughout and you should be OK. For starters, you might try keeping the tank at 150 or so psi, then regulating it down (full flow regulator) down to 125 or so psi into the pipes, then regulators for what's needed at each station.

As for the variance you're seeing between 150 and 175 psi with the current settings, you are probably currently set with the motor to cut in at around 150 and cut out at 175. If you don't need that much air, you can drop it to around 125 (or less) cut in.

06-20-2009, 04:30 AM
With the new blast cabinet, I'll be upgrading my compressor soon. But nothing that high pressure. Single stage high volume low rpm is my interest. In my opinion, you rarely need that much pressure, so you're just spending money (and wear-n-tear) pushing it up that high.

But, you certainly want to drop the pressure at ports where valve'd air tools are in use. That much pressure will blow the rubber seats right out of them. I've got a Snap-On air ratchet and a Snap-On DA (IOW, not cheap junk) that both need rebuilds because I ran them at 135 one time to many...

06-20-2009, 04:37 AM
There are several "pressure" issues here.

The pressure in the tank will be pretty well "static".

As soon as air moves across/along anything in the system, there will be a "pressure drop" across the item in the line/system. Theoretically, when there is no air use or demand there will be no pressure drops and the pressure (unless reduced by a regulator) will be the same everywhere. Some of the largest losses are "line losses" due - mainly - to air/pipe friction, air speed in the line and the size of the pipe. There are considerable air pressure losses (drops) across bends/elbows, regulators, valves, filters, oilers etc. - all before it gets to the tool.

The two key requirements are air receiver (aka "tank") pressure (psi) and delivery rate (cubic feet/min) to the regulator and the line. The line losses from the regulator must be adequate to deliver the pressure and volumes/s required to/at the tools.

A "90 psi" tool will require air at a minimum of 90 psi with an air delivery volume according to its specs. That's all very well for a single-compressor > single-tool (at a time) set-up but is quite different where multiple tools at different distances with their unique air delivery requirements with a random chance of more than one at any one time having to be serviced/provided with air.

Once you get above the normal 105psi (7 bar) pressure compressor the regulators, filters etc, get a lot more expensive - especially the more efficient ones.

Tyres and "rattle guns" require a lot of air - but so does a reasonable plasma cutter (lots) - which rely on air for both cutting and cooling as well and which do not take kindly to loss of air.

So - in short - work "back-wards" from the tool to the compressor to see how they match and the maximum demand that the tools will demand and that the compressor (and the lines and system) can deliver both continuously and intermittently.

But from a more practical aspect, the "Rules of thumb" that have been developed over many years work very well.

06-20-2009, 08:55 AM
Standard Sch.40 malleable black iron fittings are rated at 150#. While the added 25# is probably not a problem, in a commercial installation, the safety & health folks won't be happy if they see it.

What is the maximum pressure needed? Running at higher pressures than needed is a waste of money. It can add a bit of reserve, but it is better to size the compressor adequately in the first place and run it at the lowest pressure needed to provide an adequate air supply at all points of use.

06-20-2009, 05:13 PM
I turned it down to 150 pSI. I was surprised that it crept up to 175 bye itself as before (months ago) i had set it at 150 after 100 psi was just too anemic. The large 1.250 diameter black pipe helped a lot. thanx for ypure insight Appreciated Mike (PS I have had a air gun blow up or fall apart allready but was chinese probably like all else is nowadays)

Quetico Bob
06-20-2009, 05:27 PM
Why 150 ? What am I missing and have not been told? Need to know the advantage. Have always relied on the usual preset of 120-125, is this just a safety margin?

Cheers, Bob

06-20-2009, 08:41 PM
150 is so the nitrogen membrane system maintains the necessary volume for all the things running of it .

06-20-2009, 09:04 PM
Mike what is this nitrogen membrane system. What are you running off of it?

Rob :)