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2-21
B8 port
Body seat
A9
Piston chamber(b)
Check valve
Lock valve
chamber
Pilot piston
chamber(a)
Pb8'
Piston B
Piston A1 Needle
valve
Lock valve
Operation of boom lock valve (release)
Dr2
Orifice
Needle valve seat
R35Z72MCV16
Release
When the pilot pressure is applied to the pilot port (Pb8') for boom lock valve release, the piston
(B) moves rightward to open the needle valve through the piston (A1).
Then, the oil returned from the boom cylinder flows through the passage in the direction of lock
valve's orifice
Ą
lock valve chamber
Ą
needle valve seat
Ą
check valve into the lock valve's
downstream side chamber (boom section).
When the lock valve's downstream chamber is connected to the tank passage after the boom
spool changeover and the needle valve is released, the pressure in the lock valve chamber
decreases to open the lock valve by the oil returned from the boom cylinder. The returned oil flows
into the tank passage with the boom spool's notch to operate the cylinder.
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