Specifications

Rated Flow: See Figure 1. page 9.
Frequency Response: Servo or Proportional Valve frequency
response will vary with signal amplitude, supply pressure, and
internal valve design parameters.The typical response varies with
supply pressure as expressed by the change in frequency of the
90˚ phase point, as shown in figure 2. Note that Direct Drive Valve
response is independent of system pressure.
Step Response: Servo or Proportional Valve step response will
vary with amplitude, supply pressure and internal valve design
parameters. See individual series catalogs for specifications. Full
amplitude step responses will normally exhibit a straight line
portion which represents flow saturation of the pilot stage.The
slope of this straight line portion will vary with the square root
of the change in supply pressure.
Flow–Load Characteristics: Control flow to the load will
change with various combinations of load pressure drop and
electrical input, as shown in figure 3.These characteristics closely
follow the relationship.
Internal Leakage: There are two sources of internal leakage;
first, flow through the hydraulic amplifier (known as “tare flow”)
which is relatively constant, and second, flow around the spool
which varies with its position. Maximum internal leakage occurs
at null. See individual Servo and Servo-Proportional Valve catalogs
for specifications.
Spool Driving Forces: The maximum hydraulic force available
to drive the second-stage spool will depend upon the supply
pressure, multiplied by the end of the spool. In the case of
Direct Drive Valves, spool driving force is created by the linear
force motor and does not change with supply pressure.
Pressure Gain: A measure of the change in control port pressures
as the input current is varied about the zero flow point. Pressure
gain is measured against a blocked load under no flow conditions.
Normally the pressure gain exceeds 30% of the supply pressure
for 1% change in rated current and can be as high as 100%.
Null Bias: Input current to the valve required to adjust the
output to zero flow. Most Moog Inc. valves have mechanical
adjustments which allow the null bias to be externally adjusted.
10
HYDRAULIC CHARACTERISTICS
80
60
40
20
-20
-40
-60
-80
-40-60-80
-80-60-40-20
100% INPUT CURRENT
100
-100
-100
-100
LOAD PRESSURE DROP–% SUPPLY PRESSURE
CONTROL FLOW–% RATED FLOW
25%
50%
75%
75%
50%
25%
100%
-20
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0 1000 2000 3000 04000 5000
LINEAR SCALE SUPPLY PRESSURE (PSI)
Fp
Fref
=
natural frequency at other pressures
natural frequency at 3,000 psi (210 bar)
Fp
Fref
Q
L
= Q
NL
i P
V
where:
Q
NL
= no-load flow at
1,000 psi drop for
Servovalves and
150 drop for P.V.
i = actual/rated current (%)
P
V
=(P
S
– P
R
) – P
L
P
S
= supply pressure
P
R
= return pressure
P
L
= load pressure drop
Q
L
= control flow
to the load
FIGURE 3
CHANGE IN CONTROL FLOW WITH
CURRENT AND LOAD PRESSURE
FIGURE 2
FREQUENCY RESPONSE CHANGE
WITH PRESSURE