Solenoid-operated pilot type spool valve

A solenoid-operated pilot type spool valve, comprising:

• a main valve portion that includes
• a valve body having input, output, and exhaustion ports,
• a valve hole formed inside the valve body so as to penetrate the valve body and so as to be in communication with the ports,
• a spool that is inserted into the valve hole so as to be slidable in an axis direction of the valve hole, the spool opening and closing flow passages that connect the ports to each other, and
• a pilot passage that is formed inside the spool, the pilot passage being in communication with the input port at all times irrespective of an operating position of the spool;
• and
• a pilot valve portion provided at an end portion of the valve body;
• the pilot valve portion that includes
• a piston box connected to the valve body,
• a pilot piston that is formed so as to be continuous with an end portion of the spool and that is accommodated inside the piston box in a slidable manner, the pilot piston having a diameter that is larger than a diameter of the spool,
• a first pressure receiving chamber and a second pressure receiving chamber that are partitioned on one side and the other side of the pilot piston,
• a constantly open communication passage that is formed in a continuous portion between the spool and the pilot piston so as to communicate the pilot passage and the second pressure receiving chamber to each other at all times,
• an opening/closing communication passage that is formed in the piston box so as to communicate the pilot passage and the first pressure receiving chamber to each other through a pilot valve, and
• the pilot valve of a solenoid-operated type that opens and closes the opening/closing communication passage.