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.
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.
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.
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:
|753.6 cu.in./min.||= 0.436 cu.ft./min. (of 80 PSI air)|
|80 PSI + 14.7 PSI||= 6.44 (times air is compressed when at 80 PSI)|
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.