COMPONENT OPERATION / Pilot Valve Counterweight (Optional) / Auxiliary (Optional) Pilot Valves In Neutral (Output Curve: A to B) 1. When the control lever is in neutral, spool (7) completely blocks pressure oil from port P. 2. As the output port is connected to port T through the passage in spool (7), pressure in the output port is equal to that in the hydraulic oil tank. 3. When the control lever is slightly tilted, cam (1) is moved and pusher (2) compresses return spring (6) downward with spring guide (4) together. 4. At this time, spool (7) is pushed by balance spring (5) and moved downward until dimension (A) be- comes zero (port P is aligned with the hole). 5.
During this movement, the output port is con- nected to port T so that pressure oil is not supplied to the output port. During Metering or Decompressing (Output Curve: C to D) 1. When the control lever is tilted further, the hole on spool (7) is connected to the notch. 2. Pressure oil in port P flows into the output port through the notch and the hole on spool (7), and pressure in the output port increases. 3. Pressure in the output port acts on the bottom surface of spool (7) and spool (7) is moved up- ward. 4. When the force to move spool (7) upward is smaller than balance spring (5), balance spring (5) is not compressed. 5.
Therefore, as port P is kept connected to the output port, pressure in the output port continues to increase. 6. When pressure in the output port increases further, the force to move spool (7) upward increases. 7. When this force becomes larger than balance spring (5), spool (7) compresses balance spring (5) and moves upward. 8. When spool (7) moves upward, the notch is closed. As pressure oil from port P does not flow to the output port, pressure in the output port stop increasing. 9. As spool (7) is moved downward and balance spring (5) is compressed, pressure acting on the bottom surface of spool (7) increases until pres- sure balances with the increasing spring force.
This increasing pressure becomes pressure at the output port. NOTE: The lever stroke while pressure at dimen- sion (A) becomes zero is play. E F Pilot Pressure D C B A Pusher Stroke T523-02-05-001 T3-4-10