Solenoid valves - Bürkert Fluid Control Systems

1.4.
Stroke-force behavior
of DC and AC
solenoids
The pick-up forces acting on the core
are very greatly influenced by the core
stroke (air gap). The greater the stroke,
the lower the pick-up forces will be.
This interrelationship is referred to as
stroke-force.
In addition to the spring force for returning
the core, fluidic forces, triggered
by the medium pressure, also act
in opposition to the pick-up force of
the solenoid coil.
The stroke-force behavior of DC coils
differs with respect to AC coils with
the same electrical active power by
virtue of the fact that the magnetic holding
forces of the DC coil are higher
with the solenoid core energized. However,
the pick-up forces with the solenoid
core dropped out are generally
lower. Referring to the functions of the
valve, this means that, in many cases,
higher pressures can be switched with
AC voltage. Often, this DC coil deficit
can be compensated for with a special
design of the solenoid core and stopper
geometry (profiled armature).
There are also other different characteristics
in addition to the differing
stroke-force behavior:
DC solenoid
■ Quieter
■ Less wear of solenoid core
■ High solenoid holding force
■ Same pick-up and holding power
■ No shading ring required.
AC solenoid
■ Tendency to hum
■ Risk of burn-out of the solenoid
coil if solenoid core is jammed
■ Faster switching speed (dependent
on phase angle).
.
Magnetic force
AC
Magnetic force
DC with profiled
armature
DC
Stroke
DC without profiled
armature
Stroke
Stroke-force characteristic curve
for DC and AC coils
Stroke-force characteristic curve
for coils with and without profiled
armature
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