REED B50HPG, Technical Manual, Page: 21 / 235

OPERATION and MAINTENANCE
Rev 1.2 20 of 80
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MAIN PUMP CIRCUIT OPERATIONAL SEQUENCE
It can be noted in the schematic and the diagram below that the main pressure and flow
is only directed to one side of the hydraulic drive cylinder. In this instance, it is directed
to the head side or piston side of the double acting drive cylinder.
The hydraulic drive cylinders are identical. Because only one cylinder is pressurized at a
time, a means is required to assist in the retraction of the opposite cylinder. This is
accomplished by connecting the rod sides of the cylinders together, forming a slave loop.
In so doing, the hydraulic fluid that exists in the rod side of the extending cylinder (CYL
“A”) is transferred to the rod side of the other cylinder (CYL “B”) causing it to retract
simultaneously. The oil in the head side of CYL “B” is then forced out as it retracts and
free flows through the directional valve back to the hydraulic tank or system.
With this arrangement of connecting the two cylinders together, it is possible for various
reasons, such as leakage around the piston seals, that more oil exists on the rod side of
the cylinder than is required. When this condition exists, some hydraulic oil remains at
the rod end of the cylinder being extended while the other cylinder is fully retracted. As a
result, the cylinder will not completely extend and thus short strokes, which will also
happen to the other cylinder on the next cycle.
This condition can be corrected by actuating and holding the STROKE CHANGE switch
on the electrical control box until extending cylinder is fully extended. Hydraulically, this