# Problem: Size an Air Compressor and Receiver

A company has a machine that uses 50 cfm at 100 psi. Size an air compressor in SCFM that will have a duty cycle of 40%. Then size an air receiver in gallons that would supply that SCFM for three (3) minutes with the pressure dropping from 100 psi to 80 psi.

##### Find Out The Solution

I have two equations that I use for sizing an air compressor with a duty cycle:

**SCFM = CFM X C.R./Duty Cycle **

**CFM = SCFM/C.R./Duty Cycle**

*Note: (C.R.) is the compression ratio. **These two equations cannot be transposed into the other equation.*

**Step 1:** Find C.R.

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

We are looking for SCFM, so let’s use the first equation and substitute in our numbers.

**Step 2:** SCFM = 50 X 7.8 / 0.40 = *975 SCFM* per machine.

We multiply the CFM by the C.R. to get SCFM and then we divide by 0.4 to oversize the compressor so that it will only run 40% of the time, allowing for expansion of our system in the future.

**Sizing of a Receiver Tank**

Again I have two equations, one for sizing the tank in cubic feet and one for sizing in gallons:

T(min.) = V(cu.ft.) X (P_{2}-P_{1})

14.7 X SCFM

T(min.)=V(gal.) X (P_{1}-P_{2})

110 X SCFM

We are looking for the receiver size in gallons, so let’s use the second equations.

3 X 110 X 975 / 20 = *16,087.5 gallon receiver per machine*

3 is time in minutes, 110 is a constant, 975 is the SCFM, 20 is the pressure drop (P_{2}-P_{1})

*The answers are 975 SCFM **and 16,087.5 gallon receiver per machine. *

### Deadline past. Not available for submissions.

*Winner:*

**Jeremy Palm,** CFPS, Hennepin Technical College, Eden Prairie, MN

*Answered Correctly:*

**Richard Throop,** CFPAI, CFPMT, CFPMM, CFPS, Neff Engineering, Flint, Michigan

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.

Tagged air, compressor, receiver, teaser

Great work by both of the student special the winner Jeremy Palm and bit hard luck for Richard Throop not selecting as a winner.

good infomation.