When compressed (pilot) air is admitted through threaded port d in cover 1, spool 2 is shuttled to the left (as shown). After this, the supply of compressed air is shut off and port d is connected to the atmosphere. Through a pusher, spool 2 shifts auxiliary plunger 7 so that valve member 8 closes the passage from space 9 to space 10, which is constantly connected to the atmosphere. After the spool is shuttled, air from the main (port 3) passes through port 4 to the operating device. At the same time, air from port 4 passes through internal channels of the valve body into space 9 and through the metering orifice in connection 5 into space 6. Since the effective area at the left end of plunger 7 is greater than that at its right end, after a certain time delay, required to fill space 6, plunger 7 begins to shift to the right. During the initial part of its motion, it opens valve member 8 and, consequently, space 9 is connected to the atmosphere. As a result, the motion of plunger 7 is accelerated and, by means of the pusher, it shuttles spool 2 to its initial position (at the right). Thus, as a pulse signal (pilot air) arrives, it operates the directional valve which, after a time delay, is returned to its initial position. The length of the time delay can be regulated by changing the volume of space 6. This is done by turning screw 11. The principle of the valve is shown schematically in Figs. b and c.
$3667$SHP,FC$