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Hydraulic
and Pneumatic Knowledge |
Products
and Services Directory
Fluid
Power Equipment
Variable-Displacement Pump. The illustration below, shows a
closed-center system with a variable-displacement pump in the neutral mode. When
in neutral, oil is pumped until the pressure rises to a predetermined level. A
pressure-regulating valve allows the pump to shut off by itself and maintain
this pressure to the valve. When the control valve is operating, oil is diverted
from the pump to the bottom of a cylinder. The drop in pressure caused by
connecting the pump’s pressure line to the bottom of the cylinder causes the
pump to go back to work, pumping oil to the bottom of the piston and raising the
load. When the valve moves, the top of the piston connects to a return line,
which allows the return oil that was forced from the piston to return to the
reservoir or pump. When the valve returns to neutral, oil is trapped on both
sides of the cylinder, and the pressure passage from the pump is dead-ended.
After this sequence, the pump rests. Moving the spool in the downward position
directs oil to the top of the piston, moving the load downward. The oil from the
bottom of the piston is sent into the return line.
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