Pneumatic valves control the path of the compressed air. The direction of flow is indicated by an arrow. Actuation can take place manually, mechanically, pneumatically or electrically. Automated systems generally use solenoid-actuated valves that form the interface between pneumatic and electrical control. They are switched by means of the output signals from the signal control section and shut off or open connections in the pneumatic power section. The main functions of electrically-actuated directional control valves include:
• connecting or shutting off the compressed air supply,
• retracting and advancing cylinder drives.
Pneumatic valve designations and symbols
Pneumatic valve actuation types
How to Control a single-acting cylinder ?
The figure shows a solenoid-operated valve that controls the movement of a single-action cylinder drive. It has three ports and two switching positions.
• When the solenoid coil of the directional control valve is de-energized, the cylinder chamber is discharged through the directional control valve. The piston rod is retracted.
• When current is applied to the solenoid coil, the directional control valve changes and the cylinder chamber is pressurized. The stem advances.
• When the current no longer applies to the solenoid coil, the valve changes again. The cylinder chamber is exhausted and the piston rod retracts.
How to Control a double-acting cylinder ?
The double acting cylinder in the figure is operated by a directional control valve with five ports and two switching positions.
• When the solenoid coil is deactivated, the left cylinder chamber is depleted and the right cylinder chamber is pressurized. The piston rod is retracted.
• When electric current is applied to the solenoid coil, the valve changes. The chamber of the left cylinder is pressurized and the chamber of the right cylinder is exhausted. The stem advances.
• When the current is no longer applied to the solenoid coil, the valve backs up and the piston rod retracts