The valve shown in Figure is a 4/2 way valve pneumatically operated DCV. Switch over is effected by direct application of pressure.
If compressed air is applied to pilot spool through control port 12, it connects port 1 with 2 and 4 is exhausted through port 3.
If the pilot pressure is applied to port 14, then 1 is connected with 4 and line 2 exhausted through port 3.
On disconnecting the compressed air from the control line, the pilot spool remains in its current position until spool receives a signal from the other control side.