IV-49
HYDRAULIC UNITSCONTROL VALVE
T7D206
5
C
4
A1
6
A
B
F
F1
T7D208
C
6
T
B
T7D209
A3
8
A2
B
T
T7D207
75
T
Port Relief Valve
Relieving Operation
When the pressure in the circuit is low with respect
to the set value, the relief valve is maintained at
equilibrium. Pressure from the pump passes from
chamber B to the orifice in piston (4), then reaches
chamber C and the needle valve (5). On the other
hand, forces F and F1 are acting in the arrow direc-
tions on both sides of the main poppet (6).
F = P × A F1 = P × A1
P: Pressure A, A1: Sectional Area
Since the sectional area of A is less than that of A1,
the main poppet (6) is pushed by the force “F1-F” to
the seat surface on the left side.
If the pressure in the circuit becomes higher than the
force of the spring (7), the needle valve (5) is pushed
to the right by hydraulic pressure, opening. Oil then
flows around the circumference of the needle valve
(5) and passes through the slits, flowing into the tank
passage T.
Compared to the chamber B side, the pressure in
chamber C is low and there is no equilibrium in
pressure. For this reason, the main poppet (6) opens
and pressurized oil flows to the tank passage T.
Suction Operation
When the cylinder is operated at high speed, and
the supply of oil cannot keep up with it, creating a
vacuum in chamber B, oil is supplied from the tank
side, preventing the occurrence of cavitation.
When the pressure in chamber B is lower than the
pressure in the tank passage T, the differences in the
sectional areas A2 and A3 cause the poppet (8) to
open. Thus, sufficient oil from the tank passage T
enters chamber B, filling the empty space.
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