Structure And Function - Kubota K008-3 Workshop Manual

d. Structure and function
(1)Relief valve function
P
Inner parts, relief valve
(2)Anti cavitations valve function
(4)
(1)
(3)
(4)
Inner parts, anti-void valve
A
E
B
T
D
C
(2)
(4)
(1)
(3)
(4)
(2)
(1) (2)
(Operating mechanism of the relief valve)
The higher the working load rises, the higher the circuit
pressure goes up. At a preset pressure level, however,
the relief valve gets activated. When the sircuit pres-
sure has reached the setting of the pilot valve spring
(D), the oil flows through the orifice of the main poppet
(A) into the main poppet spring chamber (E). This
pushes up the pilot poppet (C) and lets the oil flow into
the tank. Now a pressure difference takes place across
the orifice of the main poppet (A), and the main poppet
(A) gets released the seat. In this way, the pressure oil
starts flowing out of the circuit to the tank, which keeps
the circuit pressure at a preset level.
Check point
(1) To seeif the relief valve itself is in trouble, replace it
with new one of the same pressure level and check
for similar sympom.
(2) The relief valve malfunctions probably due to for-
eign matters that are caught in between the poppet
(A to C) and the seat. Carefully check these parts
for dust, metal chippings and the like. Check also
the seat for dents and repair it as required.
(3) Check the springs for looseness and the seals for
degrading.
If the pressure (3) at the cylinder causes cavitation, the
anti-void valve opens itself, feeding the oil from the tank
and filling the space.
(1) The cylinder port pressure (3) is applied over the
large area at the back of the O-ring, which activates
the poppet (3) and its seat.
(2) When the pressure (3) drops below the atmosphiric
pressure, the tank pressure (4) applies upon the cir-
cular area between A1 and A2. This pressure will
overcome the cylinder port pressure and the force
of the spring (2), thereby opening the poppet (1).
(3) With the space full of oil, the spring forces back the
poppet and the cylinder port presure (3) works
tightly upon the seat.
Check point
(1) Check the poppet seat for scratches, the spring for
looseness and the seals for degrading.
IV-M-23
Courtesy of Machine.Market