Air Consumption

Air consumption is a function of the volume of a cylinder, the cycle time, and the inlet air pressure. It is generally expressed in Standard Cubic Feet Per Minute (SCFM) of free air, where "Standard" means at a temperature of 70°F and at sea level (standard atmosphere). Depending on the size of the cylinders and their cycle times, air consumption can vary widely on pnuematic projects, and the cost of the compressed air can be a very significant (often overlooked) cost of a pneumatic system. In many cases, the cost of the compressed air can dwarf the cost of the pneumatic components over the life of a machine or process.

Interactive Air Consumption Calculator (for Cylinder Only):

The formula for calculating the air consumption of a cylinder is shown below, enter your own values for Bore size, stroke length, cycles per minute and inlet pressure to see the SCFM that will be consumed. A "long hand" example calculation is also shown below.

Select Bore
Size:
1/4" 7/16" 1/2" 9/16" 3/4" 1" 1-1/16" 1-1/8" 1-1/2" 2" 2-1/4" 2-1/2" 3" 3-1/4" 4" 5" 6" 8" 10" 12"

Enter Stroke
Distance(in)

Enter Cycles
per Minute

Select Inlet Pressure
(Cf Compression
Ratio lookup):
10 PSI 20 PSI 30 PSI 40 PSI 50 PSI 60 PSI 70 PSI 80 PSI 90 PSI 100 PSI 110 PSI 120 PSI

	2(Area × Stroke) × Cycles	× Cf Ratio	= ? SCFM
	1728 in³/ft³

Interactive Air Consumption Calculator (for Tubing Only):

Depending on the size and length of the tubing between the valve and cylinder, you may also wish to calculate the air consumption of the tubing - it can be significant. This tubing consumption calculator assumes a double-acting cylinder with supply tubing of the same length on both the extension and retraction ports . If you are using a spring return cylinder (with a single supply line) simply divide the answer by 2.

Select Tubing
Diameter (OD):
5/32" 1/4" 3/8" 1/2" 4 mm 6 mm 8 mm 10 mm 12 mm 16 mm

Enter Tubing
Length(in)

Enter Cycles
per Minute

Select Inlet Pressure
(Cf Compression
Ratio lookup):
10 PSI 20 PSI 30 PSI 40 PSI 50 PSI 60 PSI 70 PSI 80 PSI 90 PSI 100 PSI 110 PSI 120 PSI

	2(Area × Length) × Cycles	× Cf Ratio	= ? SCFM
	1728 in³/ft³

Calculation Example (for Cylinder Only)

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

1. Find the area of the piston by converting the bore diameter into square inches (Πr²)

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

2. Determine consumption per single stroke

3.14 sq. in. x 4 in. 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 the volume of compressed 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 cubic inches to cubic feet

753.6 cu.in./min.	=  0.436 cu.ft./min. (of 80 PSI air)
1728 cu.in/cu.ft.

6. Determine ratio of compressed air at 80 PSI to "free"; uncompressed air (at standard atmospheric pressure). If you are operating other that at sea level or 70 degrees F, you may need to adjust the 14.7psi constant.

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

7. Apply ratio to determine cubic feet of free air used per minute

0.436 cu. ft. x 6.44 compression ratio = 2.81 cu. ft. of free air used per minute

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