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 (e.g. manual override, if present)

Each actuation symbol is drawn on the side of the switching positions that corresponds to its direction of action.

Piloted valve, electromagnetically actuated at both sides, manual override

Mechanical components Spring return

Table 5.4: Actuation methods of directional control valves

5.3 2/2-way valves

The 2/2-way valve has two ports and two switching positions (open, closed). This valve does not have an exhaust function in the closed switching position (unlike the 3/2-way valve). The most frequent design is the ball seat.

The 2/2-way valve can be manually, mechanically or pneumatically actuated.

5.4 3/2-way valves

The 3/2-way valve can be used to set and reset signals. It has three ports and two switching positions.

The 3/2-way valve can be manually, mechanically, solenoid or pneumatically actuated. The actuation method is determined by the control requirements.

5.4.1 3/2-way hand slide valve

This manually operated valve has a simple design. It is operated by sliding the grip sleeve (1) in longitudinal direction. This valve is used as an on-off valve, mainly for pressurising and exhausting control systems or parts of systems.

1 2

3

1 2

3 1

Figure 5.5: 3/2-way hand slide valve – sectional view and symbol

5.4.2 3/2-way stem actuated valve

The design of this mechanically operated valve is based on the disc seat principle. The seal is simple and effective. The response time is short. A small opening movement permits a large cross section for the air to flow through. Like the ball poppet valves, these valves are also insensitive to dirt and therefore have a long service life. 3/2-way valves are used for control systems with single-acting cylinders or for actuating control elements.

Figure 5.6: 3/2-way stem actuated valve, normally closed, disc seat; left: unactuated; right: actuated

In a valve with normally open position, port 1 to 2 is open in the normal position. The valve disc seat closes port 3. When the valve stem is actuated, supply port 1 is closed by the stem and the valve disc is lifted away from the seat. The exhaust air can then escape from 2 to 3. When the valve stem is no longer actuated, the return spring returns the valve stem and the valve disc to their initial position. The compressed air flows again from 1 to 2.

5.4.3 3/2-way pneumatic valve

The 3/2-way pneumatic valve is actuated via a pneumatic signal at inlet port 12. Figure 5.8 shows a pneumatically actuated valve with spring return in closed position.

12

2

3 1 12

2

3

1

12

2

3

1 2

3 1 12

Figure 5.8: 3/2-way pneumatic valve, normally closed, pneumatically actuated, with spring return; left: unactuated; right: actuated

The valve stem is reversed against the return spring by pressurising the control piston at port 12. Ports 1 and 2 are connected. After pilot port 12 is exhausted, the control piston is returned to its initial position by the integrated spring. The disc closes off 1 from 2. The exhaust air from working line 2 can be exhausted via 3. The 3/2-way pneumatic valve with spring return can be used in closed position and open position.

A pneumatically actuated valve can be used as a control element for indirect actuation. The signal for advancing the cylinder 1A1 is triggered indirectly via the manually operated 3/2-way valve 1S1 that forwards the control signal to the control element 1V1.

For the open position, ports 1 and 3 simply have to be connected inversely to the closed position. The head of the valve with pilot port 12 can be rotated 180°. The pilot port is then designated 10.

2

3 1 10 10

2

1

3

Figure 5.9: 3/2-way pneumatic valve, normally open, pneumatically actuated, with spring return, unactuated

5.4.4 3/2-way solenoid valve

A: Manual override

Figure 5.10 shows two sectional views of a solenoid actuated 3/2-way valve.

• In the normal position, working port 2 is connected to exhaust port 3 by the groove in the armature (see close-up).

• When an electric current flows through the solenoid coil, the magnetic field exerts an upward force on the armature. The armature is lifted against the spring force. The lower sealing seat opens and the flow from pressure supply port 1 to working port 2 is opened. The upper sealing seat closes and shuts off the connection between port 1 and port 3.

• When the solenoid coil is de-energised, the spring force causes the armature to move back to its normal position. The connection between port 2 and port 3 is opened and the connection between port 1 and port 2 is closed. The compressed air escapes through the armature tube and port 3.

Manual override

Manual override A can be used to open the connection between port 1 and port 2 even if there is no current flowing through the coil of the solenoid. The screw is turned and the eccentric cam actuates the armature.

The valve is returned to its normal position by turning the screw the other way.

2

3 1

1 2

3

A A

1 2

3

A: Manual override

Figure 5.10: 3/2-way solenoid valve with manual override, closed position

A: Manual override

Figure 5.11 shows a normally open, solenoid actuated 3/2-way valve. The picture on the left shows the valve in its normal position, while the picture on the right shows the valve in its actuated position. The pressure supply port and exhaust port are swapped compared with the normally closed valve (A: Manual override

Figure 5.10).

3 2

1

A A

3 2

1

2

3 1

A: Manual override

Figure 5.11: 3/2-way solenoid valve with manual override, open position