# Problem: How Many SCFM? If the available pressure is 100 psig, how many SCFM would be saved by using an air regulator as shown in the circuit? Also what is the cost savings per year running 24/7 based on \$.40 / 1000 SCF?

Assume no hose volume.

### Given:

2″ x 10″ x 1″ cylinder

15 Cycles per minute

1 Sec. dwell when retracted

Regulator set at 20 PSI

##### See the Solution

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

### Deadline past. Not available for submissions.

By Ernie Parker, AI, AJPP, AJPPCC, S, MT, MM, MIH, MIP, MMH, Fluid Power Instructor, Hennepin Technical College, EParker@Hennepintech.edu

This teaser is printed in the Fluid Power Journal. Those who submit the correct answer before the deadline will have their names printed in the Society Page newsletter and in Fluid Power Journal. The winners will also be entered into a drawing for a special gift.

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