Applications
Directional control valves control the direction of flow of compressed air. They can be actuated manually, mechanically, pneumatically, or electrically. Directional control valves are used to connect or shut off the compressed air supply and to retract and advance pneumatic drives.
Solenoid valves
Electropneumatic control systems use electrical signals to control pneumatic devices. They combine two different energy sources: electrical energy in the signal control section and compressed air in the power section.
The interface between the two parts of an electropneumatic control system is provided by solenoid valves. Solenoid valves are switched by electrical signals from the signal control section and open or close passages in the pneumatic power section.
Actuating a single-acting cylinder
Directional control valves are used to control the movement of pneumatic devices, such as single-acting cylinders. A typical directional control valve has three ports and two switching positions.
- In the initial position, the valve connects the cylinder chamber to the exhaust port, allowing the piston rod to retract.
- When the valve is actuated, it connects the cylinder chamber to the pressure port, causing the piston rod to advance.
- When the valve returns to its initial position, the cylinder chamber is again connected to the exhaust port, allowing the piston rod to retract.
Actuating a double-acting cylinder
Double-acting cylinders are actuated by directional control valves with five ports and two switching positions.
- In the initial position, the left cylinder chamber is connected to the exhaust port and the right cylinder chamber is connected to the pressure port. This causes the piston rod to retract.
- When the valve is actuated, the left cylinder chamber is connected to the pressure port and the right cylinder chamber is connected to the exhaust port. This causes the piston rod to advance.
- When the valve returns to its initial position, the left cylinder chamber is again connected to the exhaust port and the right cylinder chamber is connected to the pressure port. This causes the piston rod to retract.
Design
Directional control valves can be divided into two groups:
- Spring-return valves: only hold the actuated switching position as long as they are actuated.
- Bistable valves: hold the most recently assumed switching position even if they are no longer being actuated.
Directional control valves are also categorized by the number of ports and switching positions they have. The valve designation includes the actuation method, number of ports, and number of switching positions, for example:
- 3/2-way pneumatic valve with spring return
- 5/2-way double solenoid valve
The design principle of a directional control valve also affects its service life, switching time, actuation method, connection method, and size. The different design types of directional control valves are:
- Poppet valves:
- Ball poppet valves
- Disc poppet valves
- Slide valves:
- Longitudinal slide valves (piston valves)
- Longitudinal flat slide valves
- Flat slide valves
Poppet valves
Poppet valves use balls, discs, flat slides, or cones to open and close connections. Valve seats are typically sealed with rubber seals. Poppet valves have few moving parts and therefore have a long service life. They are also resistant to dirt and wear. However, the required actuating force is relatively high, as the force of the integrated return spring and the air pressure must be overcome.
Slide valves
Slide valves use longitudinal slides, longitudinal flat slides, or flat slides to connect or close individual ports. In other words, slide valves use a sliding element to open and close ports. The sliding element may be oriented longitudinally (in the same direction as the flow of air) or perpendicularly to the flow of air.
Slide valves are often used in pneumatic applications because they are relatively simple and reliable. They are also available in a wide range of sizes and configurations.
Pneumatic performance data
Directional control valves are manufactured in numerous variants and sizes to meet the different
requirements of industrial applications.
Actuation methods for directional control valves
The actuation method of the directional control valves depends on the system requirements. They can include:
- Manually operated
- Mechanically actuated
- Pneumatically actuated
- Solenoid actuated
- Combinations of these
A complete representation of a directional control valve in the pneumatic circuit diagram includes
- Basic actuation method of the valve
- Reset method
- Pilot control (if present)
- Additional actuation options
