Komatsu PC500LC-10R Shop Manual page 284

COMPONENT PARTS OF HYDRAULIC SYSTEM
FUNCTION OF 2-STAGE SUCTION-SAFETY VALVE OF CONTROL VALVE
"Port (B) of the boom valve and port (B) of the service valve"
• Pressure is set to 2 stages.
• Low-pressure set is obtained by receiving pilot pressure from the attachment selector solenoid valve.
• The set pressure can be changed by turning ON/OFF the pilot pressure, corresponding to the types of the
attachments (for examples, breaker and crusher).
• The set pressure depends on the load at installed height of spring (1). (High-pressure side)
• The set pressure on the low-pressure side depends on the moving distance of the piston (2).
OPERATION OF 2-STAGE SUCTION-SAFETY VALVE OF CONTROL VALVE
When pilot pressure (P) is cut off (high pressure setting)
1.
Since pilot pressure (P) is cut off, piston (2) is pressed to
the left by the reaction force of spring (3). "Load at instal-
led height of spring (1) load < Load at installed height of
spring (3)"
2.
Load at installed height of spring (1) is maximum so that
the set pressure increases.
3.
Passage (B) is connected to the drain circuit via chamber
(C) and chamber (D).
When pilot pressure (P) is supplied (low pressure setting)
1.
Pilot pressure (P) is supplied, and it is sent through pas-
sage (B) to (A) part.
2.
Pilot pressure acts on the pressure receiving diameter (A)
part "(d1)-(d2)" of piston (2).
3.
Piston (2) is applied the pilot pressure, compresses the
spring (3), and moves to the right until it contacts to the
holder (4).
4.
Set pressure decreases since the tension of spring (1) is
lowered and the load at installed height decreases.
5.
Pressurized oil caused by the stroke of piston (2) is
drained through the passage (C) and the chamber (D).
10-190
10 STRUCTURE AND FUNCTION
PC500LC-10R
AEP2 1 6 3 1
AEP21 632