4
Section II – Description
A. General
Assembly of a typical FCGT flow control is shown in Figure
1. In general, the flow control consists of an electrical torque
motor coupled to a metering spool. The metering spool and
a compensated hydrostat stabilizes flow in the forward
direction. A check valve is provided to allow reverse free flow
through the valve.
FCGT flow controls are available in two flow ranges; 5 to 250
and 50 to 1000 cubic inches per minute, (in
3
/minute). Flow
ranges are determined by different metering spool
diameters. The smaller the metering spool, the lower the
flow range.
B. Application
Vickers application engineering personnel should be
consulted to determine correct methods of installation and
applications.
Figure 1. Cutaway view of FCGT–02–*–***–11
Torque
Motor
Hydrostat
Check
Valve
Cover
Body
Metering
Spool
Section III – Principles of Operation
A. Spool Adjustment
The metering spool is adjusted at the factory for a minimum
flow of 5 in
3
/ minute, (“A” Models), and 50 in
3
/ minute for “B”
models.
B. Theory Of Operation
Consider the FCGT Flow Control Valve as being two distinct
and separate systems – one a standard compensated flow
control with a fixed throttle setting and secondly an
electrically modulated device (torque motor), used to vary
the throttle opening. (Refer to the pictorial diagram Figure 2,
during the following explanation.)
Flow Controls
– Flow controls work on the principle that
flow through an orifice will be constant when the pressure
drop across the orifice is held constant. Flow (Q) through an
orifice is directly proportional to the orifice area (A) and the
square root of the pressure drop across it
(
D
P
Ǹ
)
.
Q
+
A
D
P
ń
0.0325
Ǹ
Q = USgpm
A = in
2
Valid for short orifice
n
P – PSI drop across orifice
Assume throttle orifice “A” (the metering spool orifice) is
opened to allow 200 cubic inches / minute, (in
3
/ minute), flow
through the valve to an external load circuit. The external load
circuit develops 1000 PSI. Inlet pressure to the valve is 2000
PSI.
Check valve
(Reverse free flow)
Spring
Spring compensated hydrostat
Inlet
Orifice “B”
Outlet
Upstream side of orifice “A”
Set screw threaded into
torque motor armature
“A” – Set for 5 in
3
/ min.
“B” – Set for 50 in
3
/ min.
Metering spool
(Throttle)
Orifice “A”
Tank drain
Pressure
Intermediate pressure
Outlet pressure
Tank pressure
Figure 2. Pictorial Diagram
