Takeuchi TB53FR, Workshop Manual

Page: 152 / 447

HYDRAULIC UNITS
CONTROL VALVE
IV-42
TB53FR
Main Relief Valve
A main relief valve is mounted between the pump
circuit and tank circuit of each inlet housing and
serves to maintain the circuit pressure at the set value.
When the Relief Valve is NOT Operating
When the pressure in the circuit is low with respect to
the set value, the relief valve maintains equilibrium.
Hydraulic oil from the pump passes through the
orifice from chamber (C) and arrives at the spring
chamber (D) and the needle valve (1). On the other
hand, forces F and F1 are acting in the respective
arrow directions on both sides of the main poppet (2).
F = P
×
A Fl = P
×
A1
P: Pressure A, A1: Cross Sectional Area
Since the cross sectional area of A is less than that of
A1, the main poppet (2) is pushed by the force
“F1-F” to the seat surface on the left side.
When the Relief Valve is Operating
If the circuit's pressure becomes greater than the set
value of the spring (3), the needle valve (1) is pushed
to the right by hydraulic pressure and oil flows to the
tank passage (T). When this happens, a pressure
differential is generated between the two ends of
orifice of the main poppet (2), and this hydraulic
pressure pushes the main poppet toward the right. As
a result, the pressurized oil in the circuit flows to the
tank passage.
This operation maintains the pressure in the circuit at
the set value.