The term single acting is used when fluid pressure is applied to only one side of the piston. The piston can only move in one direction, with a spring frequently used to give the piston a return stroke. The term double acting is used when pressure is applied to either side of the piston; any difference in pressure between the two sides of the piston moves the piston to one side or the other. PneumaticPneumatic rack and pinion actuators for water pipe valve controlsA pneumatic actuator converts the energy formed by vacuum or high pressure compressed air into linear or rotary motion. Pneumatic power is desirable for main motor controls because it can respond quickly when starting and stopping because the power source does not need to be stored in reserve for operation. Pneumatic actuators allow large forces to be produced from relatively small pressure changes. These forces are often used with valves to move membranes to affect the flow of liquid through the valve. It is responsible for converting pressure into