Specifications

HYDRAULIC
Control Flow Q
V
– The flow through the valve control ports to
the load expressed in in
3
/sec (cis), gal/min (gpm), or liters/min (lpm).
Rated Flow Q
R
– Servovalves are typically rated at 1,000 psi
drop, while Proportional Valves are rated at 150 psi drop.The
flow under no-load condition, Q
NL
, will vary with supply pressure
as shown in Figure 1.The relationship can be calculated by:
Flow Gain – The normal relationship of control flow to input
current, expressed as cis/mA, gpm/mA, or lpm/mA.
No Load Flow – The control flow with zero load pressure drop,
expressed in cis, gpm, or lpm.
Internal Leakage – The total internal valve flow from pressure to return
with zero control flow (usually measured with control ports blocked),
expressed in cis, gpm, or lpm. Leakage flow will vary with input current,
generally being a maximum at the zero level of null (called null leakage).
Load Pressure Drop ÆP
L
– The differential pressure between
the control ports (that is, across the load actuator), expressed in
lbs/in
2
(psi) or bar.
Valve Pressure Drop ÆP
V
– The sum of the differential
pressure across the control orifices of the valve spool, expressed
in psi or bar.Valve pressure drop will equal the supply pressure,
minus the return pressure, minus the load pressure drop,
[ÆP
V
= (P
S
– R) – ÆP
L
].
PERFORMANCE
Linearity – The maximum deviation from control flow from the
best straight line of flow gain, expressed as percent of rated current.
Symmetry – The degree of equality between the flow gain of one
polarity and that of reversed polarity. Measured as the difference
in flow gain for each polarity, expressed as percent of the greater.
Hysteresis – The difference in valve input currents required
to produce the same valve output as the valve is slowly cycled
between plus and minus rated current.
Threshold – The increment of input current required to produce
a change in valve output.Valve threshold is usually measured as the
current increment required to change from an increasing output to
a decreasing output, expressed as percent of rated current.
Lap – In a sliding spool valve, the relative axial position relationship
between the fixed and moveable flow-metering edges within
the null region. Lap is measured as the total separation at zero
flow of straight line extensions of nearly straight portions of
the flow curve.
Pressure Gain – The change of load pressure drop with change
of input current at zero control flow (control ports blocked),
expressed as nominal psi/mA or bar/mA throughout the range
of load pressure between ±40% supply pressure.
Null – The condition where the valve supplies zero control flow
at zero load pressure drop.
Null Bias – The input current required to bring the valve to null,
excluding the effects of valve hysteresis, expressed as percent of
rated current.
Null Shift – The change in null bias resulting from changes in
operating conditions or environment, expressed as percent of
rated current.
Frequency Response – The relationship of no-load control flow
to input current when the current is made to vary sinusoidally at
constant amplitude over a range of frequencies. Frequency response
is expressed by the amplitude ratio in decibels (db) and phase
angle in degrees (˚) over a specific frequency range.
200
100
50
40
30
20
10
5
1
0.5
0.1
100 200 500 1000 2000 3000 5000
60 gpm
@
1000 PSID
40 gpm
@
1000 PSID
30 gpm
@
1000 PSID
5.0 gpm
@
1000 PSID
2.5 gpm
@
1000 PSID
1.0 gpm
@
1000 PSID
15 gpm
@
1000 PSID
20 gpm
@
1000 PSID
25 gpm
@
1000 PSID
10 gpm
@
1000 PSID
where:
Q
NL
= no-load flow
P
S
= supply pressure
Q
R
= Servovalve rated flow
at 1,000 psi drop, P.V.
rated flow at 150 psi drop
ÆP = valve drop, typically 1,000 psi
for Servovalves and 150 psi
for Proportional Valves
FIGURE 1
CHANGE IN RATED FLOW WITH PRESSURE
9
P
S
Q
NL
= Q
R
ÆP