Problem: How Many SCFM?

First, let us calculate the compression ratio at 100 psi and 20 psi. We will need this information later.

100/14.7 + 1 =  7.8 : 1 (C. R.) at 100 psi

20/14.7 + 1 = 2.36 : 1 ( C.R.) at 20 psi

Next, calculate the effective rod in area:

cap end area – rod area = 3.14 – 0.7854 = 2.356 in² (EREA)

Now the rod end volume:  2.356 in² x 10 in = 23.56 in³ / cycle

Find CIM:  23.56 in³ x 15 cycle / minute = 353.4 CIM

Find CFM: 353.4 / 1728 (cu. in. per cu. ft.) = .20 CFM

To convert CFM to SCFM, we must multiply CFM x C.R.:

0.20 x 7.8 = 1.56 scfm @ 100 psi

0.20 x 2.36 = .47 scfm @ 20 psi

Subtract the difference to see the savings in air consumption: 1.56 – 0.47 = 1.09 scfm saved

Find saving per year: 1.09 x 60 minute = 65.4 SCF per hour x 24 = 1569.9 SCF per day x 365 per year = 572,904 SCF / year

Given: $0.40 / 1000 SCF:  572,904 / 1000 x 0.40 = $229.16 savings per year