Float Operation - Komatsu 930E-2 Shop Manual

FLOAT OPERATION (Figure 7-9)
When the operator releases the lever as the body
travels down, the hoist pilot valve spool returns to the
FLOAT position. In this position all ports (10, 12, 14, &
15) are common with each other. Therefore, the pilot
supply oil is returning to tank with no pressure build-up
thus allowing the flow control valve (2) to remain open
to allow the pump oil to flow through hoist valve port
(23) to the brake cooling circuit and eventually return-
ing to the tank.
With no blockage of either RAISE or DOWN pilot
ports (14 & 15) in the pilot valve, there is no pressure
on the top of either main spool. The oil returning from
the head end of the hoist cylinders builds pressure on
the bottom of the head end spool (8) exactly like in
POWER DOWN allowing the returning oil to transfer
to the low pressure passage (20). The back pressure
in the low pressure passage created by the primary
low pressure relief valve (22) causes pressure under
the rod end spool (7) to move the spool upward. This
connects the low pressure passage to the rod end of
the hoist cylinders.
L7-14
The 26 psi (179 kPa) in the low pressure passage
causes oil to flow to the rod end of the cylinders to keep
them full of oil as they retract . When the body reaches
the frame and there is no more oil flow from the
cylinders, the main spools center themselves and
close the cylinder ports and the high and low pressure
passages.
Hoist Circuit L07023