How to size the right size compressor?

While putting in our new machine...we could tell how taxed our old compressor was, but how do I size the right CFM's? I don't want to under size the shop but don't need the badest compressor out there.

Jay

Every piece of equipment you have should list air usage. Add em all up, then determine a percentage of simultaneous usage. Because compressors rarely put out rated CFM in the real world, I'd add 25% to that and and then round up to the next sized compressor.

Hi Jay
When I was confronted with the exact same problem, I looked around and decided to just buy another just like the one I had... And split the system... So you may have 2 motors running say 5HP each, or one 10 if you had a bigger compressor... whats the dif?...

Kinda like when I wanted to re power my boat... It had twin 125 HP... but I wanted to go faster... so how much?... 180? 200? nahhh double them...I installed twin 250 HP and yes they are more than I needed, but remember 2 things... you'l never wish you had less... and you may just need the extra at times...

It makes a huge difference, a two stage compressor with the same motor rating will outperform a single stage flat out anytime.
There´s a great writeup on compressors from Forrest somewhere here in the forum. Find it, read it.

Cheers,
Johann

Johann Ohnesorg said:

It makes a huge difference, a two stage compressor with the same motor rating will outperform a single stage flat out anytime.There´s a great writeup on compressors from Forrest somewhere here in the forum. Find it, read it.

Cheers,
Johann

Click to expand...

Performance (efficiency) as one factor, ballanced with;
How wide a band of usage you anticipate.

If you go deeper into CNC, you might get to the point
where you leave unattended opporations running.
Might be something like this..........

You find a better compressor (efficiency again) on Craigs list.
But it's not quite enough for your highest (peak) maximum needs,
now that you have added the G&L.
SO.
You have it carry the primary load, and have your currant unit
trip in if the new one falls behind.

Now when unattended time comes, you might wish to have
an isolation valveing set-up, to carry the run, but not the
whole shop which may have leakage, that isn't going to be
addressed any-time soon.

Now you use the appropriate unit for lights-out running.
Phil

a'hemmmn

Pics.?
Just a couple ? Hmmn?

Then when your Chevy arrives, park it in front of the G&L.
And take lots of pics.
m1m

Boy I have 3 vacation days left.
I could have driven her out to you.
But then theres that virginity thing.
Phil

Yup, the best way to ensure reliable air in a commercal setting is to install two compresors each having twice the CFM required with an alternating starter, a receiver having enough headroom to supply shop air for one minute between compressor cycles at the heaviest demand. Add a refrigerant air dryer and a good loop piping system with drops and filters at each station. Pretty expensive.

My BS on compressorts can be googled using "addy compressor" as search objects. It's basic intended for the home shop user not a purchaser for a commercal shop. The Granger catalog has a pretty good compressor tutorial and I think DeVilbis has sizing info someplace on its website.

Sizing a compressor system for a whole shop requires a survey of present day consumption and a crystal ball for the future. Major air sytem suppliers have engineers on staff to help you establish your requirements. It's amazing the wealth of info a good engineer can extract from a dorky customer with a few questions - and how he can use this info to cook up a series of economical to implement suggestions. If the engineers is good you will slap your own head in "how did I miss the obvious". That is if the engineer is good. A middling engineer will have more complicated and expensive solutions. Also you have to realize the best solutions are not always cheap.

Sooner or later you may be forced to look at serious air jammin' equipment like a screw compressor. Efficient, no rings or pressure lubed bearings, low maintenence - and QUIET.

The conventonal wisdom goes: you size a compressor twice the size needed for current demand. A compressor in a 50% duty cycle lasts 4 or 5 times as long as one that runs full time. I don't know why.

I kinda like small dedicated back-up compressors at each CNC station piped to cross-connect via a stop valve to the shop system. If the shop air goes down for some reason your CNC money makers still jingle the cash register.

Jay: I use a lot of air in short work sessions in my shop. What I did to cure my capacity problem was to bump up my piping pressure and add tankage. By running my piping at a little over 140 psi and putting regulators at the point of use, and adding tanks, I was able to go from about 2 minuets of usage to over 4 mins before I had to let the system catch up. Since I have moved, I found a much bigger compressor and will be ganging it with an addition tank. It will have 120 gallons capacity on the compressor itself and the gang tank is a 650 gallon propane tank. I will have enough capacity that we can run our blast cabinet continously when we need too, and not have to worry about running out of air.

Craig C.

Remember this though,

It takes a *lot* more energy to compress air to 140 psi than it does to 90 psi. It'll be cheaper in the long term to buy a larger compressor and run it at 90 psi than a smaller compressor and run 140 psi.
By dropping our main air pressure from 100 psi to 92 psi we saved, IIRC $155K in electrical costs per year. (We have 3x 450 hp screw compressors and 1x 250 hp screw compressor, so the energy savings is very significant.)

contact your industrial air compressor distributor. they can come in and attach instrumentation to not only tell you how much air you need, but also how much you have approximately in leaks, etc. I wound up with a sullair variable freq/ variable displacement compressor and its been great compared to the dinosaur ingersoll ssr ep60 I have in backup. Your dealer can tell you how much you actually need, what you buy to allow for future expansion is up to you. Many times there are utility rebates on this type of equipment.....don't forget to check it out.

Tonytn36 said:

Remember this though,

It takes a *lot* more energy to compress air to 140 psi than it does to 90 psi. It'll be cheaper in the long term to buy a larger compressor and run it at 90 psi than a smaller compressor and run 140 psi.By dropping our main air pressure from 100 psi to 92 psi we saved, IIRC $155K in electrical costs per year. (We have 3x 450 hp screw compressors and 1x 250 hp screw compressor, so the energy savings is very significant.)

Click to expand...

Excellant point!
Run wide lines, full responce at each coupling.
Lower system pressure.
Every task is quicker (even to clear some chips from a bore).

Got a demanding machine ?(some tool-changers) alarm
if there is an excessive pressure drop.
Install a small surge-tank, @ the machine with 3/4 ID line
to the toolchanger. Tank replenishes before next tool-change.
Kinda like a Capacitor assist for a HP pump-motor.

NO NEED to raise the system pressure to avert an alarm.

I agree with adding another compressor rather than buying bigger.
I used to maintain compressors at a past job. There were three compressors, two 5hp and one 10hp. I ajusted them to come on line as manifold pressure dropped to certain pressures. That way they only ran when needed.

Are you guys buying mostly just the regular fairly loud compressors, or spending a bit more for the fairly silent type on the 45-60db range?

air compressors and tool boxes are much the same
buy the biggest you can afford, or sooner or later you will be buying
again.

bob g