The air required to engage (in air engaged/spring released units) or disengage (in spring engaged/air released units) a clutch, brake, combination clutch-brake is the volume to fill the area between the cylinder and piston. Air is not consumed until it is exhausted from the unit. Air volumes are listed on the downloadable PDF detail sheets available for each catalog product on this website (click here for example). Air volumes of non-catalog products can be obtained by contacting engineering.