Page 502 - Mechatronics with Experiments

JWST499-Cetinkunt
JWST499-c07
488 MECHATRONICS Printer: Yet to Come October 9, 2014 8:41 254mm×178mm
Sol A Sol B
Stage 1
valve

Controlled
Stage 2 pilot pressures
valve to main stage
spool

Centering Centering
T A P B T
spring spring
A B

P T
FIGURE 7.64: Two-stage valve: the first-stage spool is for the pilot stage, the second-stage
spool is for the main stage.

Stage 1:
Torque motor
Symbol
A B

Stage 2:
Pilot valve
XY P T

Stage 3:
Controller
and Main
amplifier valve

Position
sensor X T A P B Y
(Main valve position feedback
to torque motor control)
FIGURE 7.65: Three-stage valve: first stage is torque motor and double nozzle flapper, second
stage spool is the pilot valve, and the third stage is the main valve. Second stage amplifies the
actuation force of the first stage to move the third stage (main spool). The X and Y letters in the
valve symbol indicate that the valve has two pilot stages. Hence, it is a three-stage valve, two
pilot stages plus the main stage. The arrow on top of the solenoid signal around the spring
indicates a valve position sensor feedback signal. The arrow over the solenoid indicates that it
is a proportionally controlled solenoid, not just ON/OFF, although this representation is often
omitted in symbol drawings. This particular valve can support flow rates upto 1500 l/min at 10
bar pressure drop across the valve (Moog series D663). Courtesy Moog Inc.