Takeuchi TB 250, Руководство по ремонту

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3-7
3
CONTROL VALVE
FUNCTION
Main relief valve
The main relief valve is mounted between the pump circuit
and tank circuit of each inlet housing, and serves to main-
tain the circuit pressure at the set value.
The relief valve remains turned off:
As long as the pressure in the circuit is lower than the set
value, the relief valve maintains a pressure equilibrium and
thus remaining turned off. The hydraulic pressure from the
pump flows through the chamber C and the orifice of the
main poppet (2) to enter the chamber D and the needle
valve (1). On the other hand, the forces F and F1 are acting
in the arrow directions on both sides of the main poppet
(2).
F = P x A
F1 = P x A1 (P: Pressure A and A1: Cross-sectional areas)
The cross-sectional area A1 is larger than the cross-sec-
tional area A, and thus the main poppet 82) is pushed to
the left seat surface by the force of “F1 - F”.
The relief valve is actuated:
If the pressure in the circuit becomes higher than the set
force of the spring (3), the needle valve (1) is pushed to the
right by hydraulic pressure and the oil flows into the tank
passage T. When this happens, a pressure differential is
generated between the two ends of the orifice of the main
poppet (2), and the main poppet is pushed to the right by
the hydraulic pressure. As a result, the pressure oil in the
circuit flows into the tank passage as shown by the ar-
rows.
This operation maintains the pressure in the circuit at the
set value.
Port relief valve
The port relief valve is located between the actuator and
the tank circuit T. It protects the actuator from a pressure
shock caused by the sudden blocking of the actuator port
or by overloading, or absorbs abnormal pressure caused
by an external force.
Relieving operation:
When the pressure in the circuit is lower than the set value,
the relief valve maintains a pressure equilibrium. The hy-
draulic pressure from the pump passes from the chamber
B to the orifice of the piston (4), then reaches the chamber
C and the needle valve (5).
On the other hand, the forces F and F1 are acting in the ar-
row directions on both sides of the main poppet (6).
F = P x A
F1 = P x A1 (P: Pressure A and A1: Cross-sectional areas)
The cross-sectional area A1 is larger than the cross-sec-
tional area A, and thus the main poppet (2) is pushed to the
left seat surface by the force of “F1 - F”.
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