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.
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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