Page 508 - Mechatronics with Experiments

JWST499-Cetinkunt
JWST499-c07
494 MECHATRONICS Printer: Yet to Come October 9, 2014 8:41 254mm×178mm
Solenoid
Armature
Coil

Ball to
Pilot pressure
control
Tank pressure pilot pressure
Output pressure
Main spool
Inlet pressure
Cavity on the Spring
manifold for
the valve
FIGURE 7.70: Examples of cartridge valves. The cross-section figure shows a cartridge valve
with a sliding spool type metering element. Reproduced with permission from HydroForce
(www.hydraforce.com).

servo valves support flow rates up to about 550 lpm at 70 bar pressure drop across the valve
(i.e., Moog D661 through D664 series). A three-stage valve where the first two stage is
either a double nozzle flapper or jet pipe type servo valve can support up to 1500 lpm flow
rate (i.e., Moog D665 and D792 series).
Cartridge valves are designed to be assembled on a manifold. A manifold can be made
of a single cartridge valve (single function manifold) or multiple valves (multi function
manifold) which is generally the case. A manifold block may typically hold multiple
cartridges and other types of valves (Figure 7.70, and Figure 7.71). Cavity sizes (diameter,
depth, tread) on the manifolds are standardized so that cartridge valves from different
manufacturers can be used interchangeably.
Cartridge valves can be categorized in terms of different criteria as follows:

1. Mechanical connection to the manifold:
(a) Screw-in type which is installed by screwing valve threads into manifold cavity
threads.
(b) Slip-in type which is installed in the manifold by a bolted cover to the manifold.
Screw-in type cartridge valves support flow rates up to about 150 lpm, and slip-in
types support flow rates above 150 lpm. The slip-in type has the advantage over
the screw-in type in that it does not squeeze the ports and hence achieves better
repeatability in the assembly. There are seven standard slip-in cartridge valve
sizes (specified by ISO 7368 and DIN 24342) where the nominal valve port
diameter is 16, 25, 32, 40, 50, 63, and 100 mm, supporting flow rates in the range
of 200–7000 lpm at about 5 bar pressure drop across the valve.
2. Metering component:
(a) Spool type: the flow metering element can be a spool similar to a standard spool
valve-body assembly. Spool type cartridge valves can be two-way, three-way,
four-way or more.
(b) Poppet type: the flow is controlled by a poppet and its seat. Poppet type car-
tridge valves are typically two-way valves. Cartridge valves use O-rings on the
stationary component of the valve body in order to seal the valve ports from each
other and minimize leakage. O-rings also help increase the damping effect on
the valve, but add hysteresis to the valve input current–flow characteristics.