JLG 600SC_660SJC Service Manual - Manual (Page 98)

SECTION 5 - CAT CHASSIS (S/N 0300128000 TO PRESENT)
5-6 – JLG Lift – 3121157
Working Principle of Shuttle Valve
The shuttle valve prevents the axial piston motor from
overheating. When the control valve is in neutral position,
no pressure exists at ports P1 and P2. Thus, the plunger is
in neutral state, blocking the oil passage to the low pres-
sure relief valve.
Shuttle Valve Action
When the hydraulic fluid discharged from the hydraulic
pump is directed to port P1 of the shuttle valve through
the control valve, the hydraulic fluid passes orifice, acts on
the end of the plunger, and tries to push the plunger right-
ward with the force in proportion to pressure against
spring on the opposite side.
When the hydraulic pressure rises to a certain pressure,
the plunger starts moving rightward, and oil passage to
the low pressure relief valve on port P2 opens. The
hydraulic fluid at port P2 passes through the notch of the
outer circular of the plunger, and acts on the low pressure
relief valve.
Figure 5-3. Structure of Shuttle Valve
P1 P2
Figure 5-4. Shuttle Valve (Shuttle)
P1 P2