Types of directional control valves: Sliding spool, poppet/diagram, rotary spool, rotary disc, slide.
Sliding spool valves
•Sliding spool valves are the most common valves used in transmission of pneumatic power to the actuator. They are available in various forms and sizes. Typical contoured spool valve with ‘0’ rings fitted into the bore is shown in Fig.
Fig. Typical contoured spool.
• The main advantages of spool valves with seals are:
1. Simple maintenance.
2. Fully balanced spool design allowing air to be without creating spool movement.
3. Relatively simple to attach controls.
4. Stroke limiters can be used.
5. Available in suitable forms.
6. Connected to any port
•The main disadvantage of spool valve, with seals are:
1. Larger body size.
2. Higher wear rates.
3. Require lubrication.
4. Continuous leakage.
5. Not suitable for high pressure applications.
6. Slower response time.
7. Require a better quality air.
•Poppet valve come in a wide variety of forms and are the most useful valve in pneumatic services. It can be used as the pilot section of a solenoid controlled valve. Poppet valve construction varies in accordance with the valve function and flow requirements as shown in Fig.
Fig. Poppet valves with open and closed transition conditions.
• The main advantages of poppet valves are:
1. Can operate with lubricant free air.
2. Can operate with inferior quality air.
3. Leak free.
4. Low wear.
5. High flow rates.
6. Rapid response.
1. Cannot be serviced.
2. Not suited to reverse porting.
3. Relatively high operating forces.
4. Air loss during change over.