SIEMENS
FLENDER Standard Couplings
Fluid Couplings — FLUDEX Series
13/5
Siemens MD 10.1 · 2015
General information
13
■
Function
Föttinger principle
Two opposing, radially bladed impellers are housed in a leak-
proof housing. The impellers are not mechanically connected to
each other. Because of the axially parallel arranged blades, the
torque is transmitted independently of the direction of rotation
and solely by the oil filling.
Hydrodynamic couplings have the characteristic properties of
fluid flow engines. The transmissible torque depends on the
density and quantity of the operating fluid and increases as the
square of the drive speed and the fifth power of the profile diam-
eter denoting the coupling size. In the driven pump impeller, me-
chanical energy is converted into kinetic flow energy of the op-
erating fluid. In the turbine impeller, which is connected to the
output side, flow energy is converted back to mechanical en-
ergy.
To generate the operating fluid circulation necessary for torque
transmission, a difference in speed is necessary between the
pump and turbine impellers. A centrifugal force pressure field is
set up that is greater in the faster rotating pump impeller than in
the turbine impeller. The difference in speed, usually termed
“slip”, at the continuous operating point of the coupling is be-
tween 2 % and 6 %, depending on application and coupling
size. Immediately after drive motor start-up slip is 100 %, i.e. the
pump impeller is driven at the speed of the motor, but the turbine
impeller remains stationary.
Slip multiplied by the transmitted power represents the power
loss of the coupling, which is converted into heat inside the oil
filling. The amount of heat generated must be released into the
environment via the coupling housing to prevent an impermissi-
ble temperature rise. The rated coupling output is mainly deter-
mined by the power loss which can be dissipated at a still ac-
ceptable operating temperature or a reasonable set slip limit.
This distinguishes the FLUDEX coupling from all positively act-
ing coupling assembly options for which the rated coupling
torque is the defining characteristic.
Depending on the FLUDEX coupling series, drive is via the inner
rotor (shaft/hollow shaft with rigidly connected blade wheel) or
via the bladed housing impeller (blade wheel housing). The driv-
ing impeller is the pump impeller, and the driven impeller is the
turbine impeller.
A low-viscosity mineral oil VG 22/VG 32, which also serves to lu-
bricate the bearings, is used as fluid. In special types water, a
water emulsion or low-flammability fluid may be used as a non-
combustible fluid.
Slip-torque characteristics for different filling levels FG
The torque characteristic depends on the oil filling quantity FG
in the coupling. This enables the transmissible torque on starting
up to be set via the filling level. With a higher filling level the start-
ing torque increases, while the operating slip and thus the cou-
pling temperature rise decreases.
Conversely, with a lower filling level the starting torque de-
creases, the coupling becomes softer, while slip and coupling
temperature rise.
R1
R2
Cu1
Cu2
Motor
Pump
Fluid coupling
G_MD10_EN_00113
Turbine
Driven
machine
Pump impeller
Turbine impeller
FG = 80%
FG = 75%
FG = 70%
FG = 65%
FG = 60%
FG = 55%
100%
0
0
50%
10%
0%
2
n
S
2
N
S
N
S
N
T
N
=
n
1
Slip
G_MD10_EN_00114
Torque
Speed
n
© Siemens AG 2015