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Page 6
Pilot Control Valve
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PILOT SYSTEM
The pilot system uses low pressure oil to operate the main control valves. The main components of the
pilot system are pump (1), pressure relief valve (3), accumulator (4), pilot cutoff valve (5) and pilot valves (6
and 7).
With the engine running, oil flows from hydraulic tank to pilot pump (1) The oil flows from the pump through
pressure relief valve (3) to pilot cutoff valve (5). The pressure relief valve maintains pilot system pressure at
37 kg/cm
2
(450 psi).
From the pilot cutoff valve the oil flows into the pilot control valves. Pilot valve (6) is a closed center valve.
The oil cannot flow through the valve when it is in the HOLD position because it is a closed center valve.
When the control lever is moved to the DUMP position, oil flows through oil lines to the ends of the bucket
spool of main control valve (8). This causes the main control valve spool to move. Movement of the spool
opens passages for attachment pressure oil to flow to the rod end of the bucket cylinder (9).
Spool movement also opens a passage for return oil from the head end of the bucket cylinder to flow back
to hydraulic tank. Attachment pressure oil acts on the rod end of the bucket cylinder and, because the
head end of the cylinder is now vented to tank, the bucket will dump.
When the control lever is moved to the CROWD position, oil flows through oil lines to the ends of the
bucket spool of main control valve (8). This causes the main control valve spool to move in the opposite
direction.
Movement of the spool in this direction opens passages for pressure oil to flow to the head end of the tilt
cylinder. Spool movement also opens a passage for return oil from the rod end of the tilt cylinder to flow
back to the hydraulic tank. Attachment pressure oil acts on head end of the tilt cylinder and because the
rod end of the cylinder is now vented to tank, the bucket will crowd.
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