Sizing an Air Compressor

[CompressorPros.com]

This might be useful for those looking to buy or upgrade their air compressor.

It can be a challenge when shopping for air compressors to get one that is going to meet your needs. First, you will need to determine if you need portable or stationary, then your available power source...do you need a gas drive or electric? What is your available voltage...Single Phase 115 or 230 Volt or Three Phase 208-230 or 460V.

Once we have answered those questions, we want to take a look at how much air you need by looking at your pressure requirements (PSI) and required volume (CFM). Single stage air compressors typically have a max pressure around 125-135 psi and two stage around 175 psi.

To get a feel for how much air (CFM) you will need, you can figure roughly 4-5 CFM per person in an automotive shop and 12-15 per person in a body shop. Once you determine the CFM you need, take that figure times 1.25 and use that total CFM to choose your compressor. For example: 3 mechanics (12-15 CFM total x 1.25 = 15 to 19 CFM) So you would look at a 5 - 7.5HP air compressor. That allows for a 75% duty cycle and should help you get a compressor large enough for your needs.

Some manufacturers state 100% duty for their piston air compressors, which not factual...most have a disclaimer saying to add 25-30% for air leaks and such, which puts them at 70-75% duty cycle. Rotary screw compressors, however, do have a 100% duty cycle.

We are glad to answer any questions that you guys might have.

 

[larry_g]

Can you speak to tank/receiver size. So many here go for tank size as the first consideration. I keep saying that tank size is the last consideration and that adding a second tank will not increase the amount of work done at the end of the day because if you have to small of a compressor increasing the receiver size just increases the work/wait numbers but at the end of the day you have done no more work because the wait time increases the same.

lg
no neat sig line

 

[zkling]

That's great info, unfortunatly this forum doesn't have a search function and the question will come up again next week.

 

[CompressorPros.com]

Tank size is definitely something that comes up. Many people think...bigger tank...more air. Manufacturers tend to build compressors with a tank that generally fits the layout. You need a certain size baseplate to hold the pump and motor, which is why you generally see smaller single stage machines on 20-60 gallon tanks, and two stage 60 gal and up.

Some people, especially when talking 7.5HP ask about a 120 gallon tank. I think that they assume that they would be getting the biggest compressor they can on single phase power.

How I address that is saying that in theory, their compressor would stay off longer with a bigger tank, it would, however, need to run longer to fill up the extra tank capacity. The Net gain is zero.

That's why it is important to look at the CFM (Cubic Feet per Minute) to see if the compressor is a good fit.

There definitely applications where big tanks are a must, but it's usually where there is a very brief need for lots of air to open a valve or door or something like that. The air is drained from the tank and then the compressor sits for a long time after refilling.

We love helping in any way we can, so if anyone wants to reach out directly, you can at [email protected]