Komatsu PC88MR-10 Shop Manual page 232

10 Structure and function
Anti-drop valve for boom
2. The pressure of chamber (a) drops. The pressure of chamber (a) becomes lower than the combined force
of the pressure of chamber (b) and spring (6).
3. Check valve (5) closes, and chamber (a) and chamber (b) are disconnected.
4. The pressure of the work equipment is held to prevent the work equipment from sudden lowering.
When the pressurized oil returns from the work equipment cylinder to the control valve
When there is no damage in the piping
1. Holding pressure of the work equipment cylinder is led to chamber (b), and it closes check valve (5).
2. The pilot pressure is led from PPC valve to port (PI). The pilot pressure is larger than the force of spring
(2) (area of circle "d").
3. Spool (1) moves rightward to the standby position. (The first stroke)
4. Chamber (a) and chamber (b) are not interconnected.
5. The pilot pressure rises further. The pilot pressure is larger than the force of spring (2) (area of circle "d").
6. Spool (1) moves rightward further, and chamber (a) and chamber (b) are interconnected. (The second
stroke)
7. The pressurized oil returns from the work equipment cylinder to the control valve.
When there is a damage in the piping
10-154 PC88MR-10