Three way valves come with three ports. These are commonly used when alternate and exhaustive pressure is required for operation, as with a coffee machine or dishwasher.
In a direct acting solenoid valve, a coil magnetically opens the valve in a direct action, lifting the shaft and the seat of the valve without depending on outside pressure.
In pilot operated valves, the plunger opens up the pilot opening while built-up pressure causes the valve to open and close. Although piloted valves require less electrical energy to operate, they usually need to maintain full power in order to remain in an open state, and they perform at a slower rate than direct acting solenoids. Direct acting solenoid valves only need full power when opening the valve, as they can hold their open position even when operating on low power.
Foot Pedal Valves are used to operate Pneumatic Cylinders. In the absence of electrical supply, manually operated valves such as Foot Pedal Valves are used. The functioning is the same, however, the solenoid coil is replaced by a foot pedal, which controls the movement of the spool inside the valve, thereby allowing the air to pass.