Daewoo Mega 500-V - Boom Float; Boom Spool Operation; Main Relief Valve; Port Relief Valve

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Main Control Valve (Toshiba)
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BOOM SPOOL OPERATION
Boom Float
When the control lever is further pushed down from the "Down" position to the "Float" position, the boom
spool moves as indicated in the illustration.
Due to this motion the neutral passage is opened. The pressure oil flows as if in neutral position. The
cylinder ports (A2) and (B2) are connected to the low-pressure oil passage. As a result, the booms float
over the ground surface according to its irregularities. The oil discharged from the boom cylinder rod side is
sent to the tail side and the oil forced out from its tail side is sent to the rod side respectively through the
low-pressure oil passage in the control valve.
RELIEF VALVE
Main Relief Valve
The main relief valve is between the neutral oil passage and the low pressure oil passage (return oil
passage) in the inlet section.
Port Relief Valve
The port relief valve is between the rod side cylinder port and the low-pressure oil passage (return oil
passage) in the bucket spool section.
The combination valve, used as the port relief valve, serves both as the relief valve and an anticavitation
valve.
Figure 4 OPERATION IN BOOM FLOAT
Reference
Number
Description
1 Port A2
2 Port B2
3 Tank Passage
4 Center By-pass Passage
5 Tank Passage
Reference
Number
Description