Page 490 - Mechatronics with Experiments

JWST499-Cetinkunt
JWST499-c07
476 MECHATRONICS Printer: Yet to Come October 9, 2014 8:41 254mm×178mm
Pump
P
T
Valve 1 (Proportional directional
Pre- flow control type) Pre- Valve 2
compensator Cylinder 1 compensator Cylinder 2
valve 1 valve 2
Tank

P
Lmax

P P
L1 L2
FIGURE 7.56: Pre-compensator valve configuration in a multi function hydraulic circuit. The
pump is of the variable displacement type. Each function is connected to the supply line in
parallel. Each compensator valve uses two pressure feedback signals for its control: the
compensator output port pressure signal and the load pressure signal (i.e., maximum of two
pressures of the cylinder it is controlling). Each compensator uses its own circuit’s load
pressure signal as feedback. In multi function circuits, the pump is controlled by the maximum
of all load pressure signals among multiple circuits. When the pump saturates (maximum flow
capacity is reached), the flow will go to the circuit with the lowest load pressure, and the
circuits with higher load pressures will get lower or no flow.

Pump
P
T
Cylinder 1 Cylinder 2

Tank

Post compensator Post compensator
valve 1 valve 2
Valve 1 Valve 2
Shutle
valve
FIGURE 7.57: Post-compensator valve configuration in a multi function hydraulic circuit. The
pump is of the variable displacement type. Each function is connected to the supply line in
parallel. Each post-pressure compensator valve uses two pressure feedback signals for its
control: the input port pressure to it and the maximum of all the load pressures among multiple
circuits. Therefore, one of the two pressure feedback signals to a post-compensator valve may
originate from a different circuit in multi circuit applications. The same pressure signal is used
for the pump control. Post-pressure compensator valves are used to equalize the flow
distribution among multiple circuits. When the pump is saturated, all circuits gets
proportionally less flow (unlike the pre-compensated case). For instance, the hydraulic
implement lift and tilt circuits of John Deere wheel loader model 644H (Figure 7.61) use the
same type of post-compensators along with each proportional directional flow control valve.