Page 487 - Mechatronics with Experiments

Printer: Yet to Come
October 9, 2014 8:41 254mm×178mm
JWST499-Cetinkunt
JWST499-c07
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 473
Pre-compensator
valve
P
A 1 P
Adjustable s
orifice P
f b1
P s P s P Δ p ~ k spring
f b2
P
P f b1
f b1 Δ p P f b2 A 2
k spring P f b2
(a) (b) (c)
FIGURE 7.54: Pre-compensator valve configuration. A compensator valve is used to maintain
a constant pressure drop across an orifice. This is accomplished by adding hydraulic resistance
(pressure drop) in a circuit. A pre-compensator valve uses two pressure feedback signals for its
control: the compensator output port pressure signal and the output of the flow control valve
following the compensator valve (i.e., maximum of two pressures of the cylinder if the flow
control valve is connected to a cylinder). The pressure drop regulated across the main flow
control valve is proportional to the spring constant of the pre-compensator valve. (a)
Component cross-section circuit diagram, (b) symbolic circuit diagram, (c) pressure
relationships.

valve is not used, most of the flow will go the valve which has the lowest load, and
other circuits will get very little flow. In order to provide equal flow on demand to
each circuit regardless of the load pressure in other circuits, a compensator valve is
used in each circuit to add additional restriction (hence pressure drop, just as a larger
load would do) in the circuit so that all circuits effectively see the same load pressure.
The pressure relationship in Figure 7.54 is as follows,
p ≥ p fb1 ≥ p fb2 (7.194)
s

Pressure feedback signal
from load of other
circuits
P A/B,2 P A/B,1
max (P A/B,1 , P A/B,2 )
Compensator
Kspring valve
P
P S
l
P
S
Tank
Main valve P S T
Cylinder

Pump P A B

FIGURE 7.55: Post-compensator valve configuration. The two pressure feedback signal
sources are the input pressure signal to the compensator valve and the load pressure. In multi
circuit configurations, the load signal is the maximum of all load signals among circuits.