JLG 600SC_660SJC Service Manual - Manual (Page 99)

SECTION 5 - CAT CHASSIS (S/N 0300128000 TO PRESENT)
3121157 – JLG Lift – 5-7
Working Principle of Relief Valve
Relief valve which determines driving and braking forces
on traveling for the vibrating roller or carrier is mounted on
the cross-line.
The structure of relief valve is differential surface direct
acting type, as is shown in
Figure 5-5.
REFRAIN FROM ADJUSTING UNLESS ANY MALFUNCTION IS
FOUND.
Working of Relief Valve
When the piston motor is driven or braked by operation of
the control valve, pressurized oil in the fore side of the
poppet passes orifice and acts on the spring chamber.
Thus, pressurized surface of the poppet becomes a differ-
ential surface (S1-S2). S1 and S2 are poppet seat surface
and poppet sliding diameter surface, respectively.
Therefore, when the pressure P at full surface of the pop-
pet becomes P = F/(S1 - S2), the poppet lifts, releasing
pressurized oil from the high pressure side to the low
pressure side.(Refer to Fig.5-1.) F: Spring set load
Working Principle of Low Pressure Relief
Valve
The low pressure relief valve keeps charge pressure of the
charge pump at necessary pressure level. The low pres-
sure relief valve is of direct acting type, as shown in Figure
5-7.
Pressurized surface of the low pressure valve becomes
poppet seat surface (S1). Therefore, when pressure P
which passes through the notch of outer circular of the
plunger and acts on the fore side of the poppet reaches P
= F/S1, the relief valve operates, releasing pressurized oil
in the low pressure side of the motor circuit to drain. F:
Spring set load
Figure 5-5. Structure of Relief Valve
Figure 5-6. Structure of Relief Valve
Figure 5-7. Structure of Low Pressure Relief Valve