5 Characteristic Curves
Dependency of flow and pressure drop
© Moog GmbH User Manual "D633-A Series" (CA80942-001; Version 1.0, 12/08) 29
5 Characteristic Curves
5.1 Dependency of flow and pressure drop
The flow that is set depends not only on the spool position but also on the pres-
sure difference
∆
p at the individual control lands.
Formula for calculating
the flow Q
A command signal of 100 % produces with a rated pressure difference of
∆
p
N
= 35 bar (508 psi) per control land the rated flow Q
N
. If the pressure differ-
ence is altered, the flow Q also changes with a constant command signal in ac-
cordance with the following formula:
Chapter "3.3.1 Open-loop flow control (Q-control)", page 16
5.2 Flow signal characteristic curve
1
Flow signal characteristic
curve
Q [l/min (gpm)] : actual flow
Q
N
[l/min (gpm)] : rated flow
∆
p [bar (psi)]
: actual pressure difference per control land
∆
p
N
[bar (psi)]
: rated pressure difference
∆
p
N
= 35 bar (508 psi) per control land
Q
Q
N
∆
p
∆
p
N
--------------
⋅
=
To avoid cavitation, the flow speed of the actual flow Q calculated in this
way at ports (A, B, P, T, etc.) must not be too great.
In typical applications the maximum permissible flow speed is 30 m/s
(approx. 100 ft/s).
1
Typical characteristic curves (measured at operating pressure p
P
= 140 bar
(2,030 psi), viscosity of hydraulic fluid
ν
= 32 mm
2
/s and temperature of hy-
draulic fluid T = 40 °C (104 °F))
command signal [%]
Figure 8: Flow signal characteristic curve
Figure 9: Setup for measuring the
flow signal characteristic curve
Q
Q
N
----
-----
---
[%
]
