Need to select a air compressor for my application

You should be able to find all the formula you need here:

http://www.compressedairchallenge.org/

in sizing of the compressor this are information you will need

1. Application

2 Maximum flowrate

3. Maximum working pressure

4. Ambient conditions

5. Required dewpoint

The above information is very important in selecting your compressor. Most of the time engineer neglect this information. They will remember this only when they have already encountered problem in the following:

1. condensation

2. pressure drop

3. energy consumption

This two problem mostly the head ache of enduser.

In calculating your compressor capacity

1 hp = 4 cfm

if you have 52.32cfm total capacity

you can calculate the HP : 52.32/4 = 13.08hp or equivalent to 15hp

with regards to the pressure and time to stop the compressor. its already in compressor features. can be adjusted by the service engineer the settings of this requirements.

the tanks size can be calculated base on compressor capacity and pressure. please see your table on thank calculation.

I hope this idea/information can help you insizing your compressor

Thanks for taking time to reply. tis information is definitely helpful.

Don't forget you are working in cu.ft. A round pipe has an area (Π*r²).

A 1/4" dia pipe has a radius of 1/8" giving an area of 0.049 sq.ins. As you are working in units of ft you need to convert the area to sq.ft by dividing by 144. This is a very small number = 0.000341 sq.ft.

Now multiply by length to get the total internal volume. 200 x 0.00034 = 0.068 cu.ft.

If compressed to 40 psig the pressure ratio is (40+14.7)/14.7 = 3.72. Multiply the Vol by this ratio to get the actual free air volume of air held in the pipe at 40 psig = 0.00126 cu.ft. If this is consumed in 15 secs, then you 4 times this amount in one minute = 0.0005 cfm.

Check my figures for accuracy on your own calculator (I have got big fingers and small buttons)

Once you have got the basic units on a common base you can equate this to your pattern of demand.

GC machines work on a puff of air so no way for the moment do you need a 15hp compressor.

thanks a lot for replying. what is 14.7 value in pressure ratio.. is it a standard formula? Also, u have multiplied the pressure ratio with 0.00034 - but total internal volume is 0.068. again, thanks for ur response its v helpful.

Pressure gauges show the actual pressure above atmospheric pressure. But all the calculations with air use 'absolute' pressures and temperatures. Therefore you have to allow for the atmospheric pressure where you are working - thus when using imperial units (feet and inches and pounds) - you have to add 14.7 psi to all gauge pressures to start with - then deduct 14.7 from the result to get back to gauge pressures when you finish.

You 40 psi is 'gauge' pressure which is in fact 54.7 psi 'absolute'. The pressure ratio is the actual change in 'absolute' pressures. Thus 54.7/14.7 = 3.72.

What this means is; your 200 ft of 1/4" pipe has an actual volume of 0.068 cu.ft - and if it held air at a gauge pressure of 40 psi - this air, if let out and measured - you would find it would occupy a volume of 0.068 x 3.72 = 0.253 cu.ft. (sorry my previous figure was a typo - clumsy fingers).

This matters because compressors are rated in 'free' air volumes. That is, the volume of air at atmospheric pressure.

So if your pipe has to be cleared every 15 secs, or 4 times a minute. Your air flow is 0.253 x 4 = 1.012 cfm.

However, this is not necessarily the actual size of the compressor, because it depends on the frequency of the purging exercise. If only carried out once per hour, the flow rate would 0.253 cf/hr.

Like others have said, you need a small receiver with a regulator and valve.

thanks for the explanation. I need the compressor to turn on once every 5-6 hrs. so if i use a 20 gallon tank, 0.133680556*20 = 2.67361112 cu ft. (assuming Compressor output =100 psi, I will reduce it down to 40 psig for my application) With pressure = 100 psig, pressure ratio = 7.802, actual volume stored in tank will be 20.86 cu ft... plz correct me if i m wrong.

can u suggest any links with basic formulas related to compressed air calculations/compressor req.

You seem to have got it right, but I take your word for the conversion from galls to cf.

Your compressor size will need to supply 20.86 cf in 5-6 hours.

Air quality will be your real problem.

There are dozens of sites with compressed air formulas - I can't say which is best.

I never worked with a GC that used air as the carrier, we always used helium or nitrogen, gas cylinders with a regulator to set the working flow. I think if you can use air, even with potential impurities, the compressor should fill a receiver tank with a pressure regulator on the outflow line. That way, the compressor will keep the tank full and the tank will run your flow. I'd still wonder about those impurities, though...

Hi....I am looking to buy an air compressor to aid in a project basement finishing of a 12' x 12' room. One tool I would like to use is a framing nailer with an air compressor to frame the partition walls. I really don't want to spend a lot of money on a compressor. Can anyone help me by suggesting an appropriate compressor ?