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Cylinder Air Consumption Rates

CYLINDERS; AIR CONSUMPTION RATES
Question: How do I calculate the air consumption of a cylinder?

Example: Determine the air consumption of a 2" bore cylinder with a 4" stroke operating 30 complete cycles (out and back) per minute at 80 PSI inlet pressure.

Answer:

1. Find the area of the piston by converting the bore diameter into square inches.

                    ( 2 in. bore / 2)x 3.1416 (pi ) = 3.14 sq.in.

2. Determine consumption per single stroke.

3.14 sq.in. x 4 inch stroke = 12.56 cu.in.

3. Determine consumption per complete cycle (Disregard displacement of piston rod because it is generally not significant).

12.56 cu.in. x 2 = 25.12 cu.in. per cycle

4. Determine volume of 80 PSI air that is consumed per minute.

25.12 cu.in. x 30 cycles/minute = 753.6 cu.in./min. of 80 PSI air

5. Convert cu.in. to cu.ft.

                    753.6 cu.in./min. = .436 cu.ft./min.

                    728 cu.in/cu.ft.

6. Convert air compressed to 80 PSI to "free" (uncompressed) air.

80 PSI + 14.7 PSI = 6.44 (times air is compressed when at 80 PSI) 
      14.7PSI

7.Determine cubic feet of free air used per minute.

.436 cu.ft. x 6.44 compression ration = .281 cu.ft. of free air used per minute

8. So, the consumption rate of a 2" bore, 4" stroke cylinder operating 30 complete cycles per minute at 80 PSI is 2.81 SCFM (Standard Cubic Feet Per Minute) of free air. "Standard" means air at a temperature of 70ƒ F and at sea level.