Patent ID: 7047993

Claim:
A pilot switching valve apparatus comprising: a pilot switching valve comprising: a valve block having a plurality of ports, and a valve chest communicating with a first pilot flow path, and a second pilot flow path; a valve spindle having a valve element provided around the periphery thereof, for switching connection among the plurality of the ports, inserted in the valve chest so as to be reciprocatively movable between two switching positions; a return spring for repulsing the valve spindle toward one of the switching positions by a urging force thereof, wherein a first pressure receiving face with an area S 1 is provided at one end of the valve spindle, on the side of one of the switching positions, the first pressure receiving face together with an inner sidewall of the valve chest forming a first pressure chamber communicating with the first pilot flow path while a second pressure receiving face with an area S 2 is provided at the other end of the valve spindle on the side of the other of the switching positions, the second pressure receiving face together with the inner sidewall of the valve chest forming a second pressure chamber communicating with the second pilot flow path; a positive pressure source connected to the first pilot flow path, for feeding a positive pilot pressure P 1 into the first pressure chamber; and a negative pressure source connected to the second pilot flow path, for feeding a negative pilot pressure −P 2 into the second pressure chamber, wherein a relationship exists such that S 1 ·P 1 ≦F 1 , S 2 ·P 2 ≦F 1 , and S 1 ·P 1 +S 2 ·P 2 >F 2 provided that an urging force of the return spring is F 1 when the valve spindle is at the one of the switching positions, and an urging force of the return spring is F 2 when the valve spindle is at the other of the switching positions, so that only when the positive pilot pressure P 1 and the negative pilot pressure −P 2 are concurrently fed from the positive pressure source and the negative pressure source into the positive pressure chamber, and the negative pressure chamber, respectively, displacement of the valve spindle from the switching position on the side of the positive pressure chamber to the switching position on the side of the negative pressure chamber takes place, thereby effecting switching of connection among the plurality of ports.