The Different Types of Piston Valve

Normally Closed (NC)

The supply is over seat (port 1).

The pilot medium to open the valve, the spring force to close it. The medium pressure acts in the direction of the valve closing.

Normally Open (NO)

The supply is under seat (port 2).

The pilot medium to close the valve, the spring force to open.

Double Acting (DA)

The supply is either over or under seat.

Since there are no springs, the pilot medium is used both for closing and for opening the valve, therefore 2x pilot valves or 1x 5/2 valve is used.

Bi-directional (bd)

This is another version of the normally closed type which allows the supply both over and under seat.

The force under the seal is obtained by using a stronger spring (or two combined springs), a solution that penalizes the performances of the valve used with flow direction over seat.

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