S0709455K
Page 9
Main Control Valve (Toshiba)
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OPERATION (PORT RELIEF VALVE)
In the Inoperative State
The pressure oil at the cylinder port (HP) flows
through the hole in the piston poppet (1) to act
from the opposite sides of the check valve
poppet (2) and relief valve poppet (3). Owing to
the difference in area on which the hydraulic
pressure acts, both poppets close to seat the
same time.
Operation (A)
When the pressure at the cylinder port (HP)
rises and exceeds the relief pressure setting,
the pilot poppet (4) opens. The pressure oil
flows from the pilot poppet into the low-pressure
oil passage (LP), passing between the check
valve poppet (2) and the housing (5).
Operation (B)
As the pilot poppet (4) opens, the pressure at
the back of the piston poppet (1) lowers to move
the piston poppet (1). As a result, the hole in the
piston poppet (1) is closed so that the pressure
at the back of the relief valve poppet (3) drops
further.
Figure 8 IN INOPERATIVE STATE
Figure 9 OPERATION (A)
Figure 10 OPERATION (B)
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