© Siemens AG 2015 FLENDER Standard Couplings Fluid Couplings — FLUDEX Series General information ■ Function Fцttinger principle Fluid coupling Pump impeller Turbine impeller Cu2 Cu1 R1 R2 Motor Driven machine Pump Turbine G_MD10_EN_00113 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. 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. 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.
G_MD10_EN_00114 Torque 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.
T N 0 0 = n 1 Slip n 100% 50% 10% 0% 2 Slip-torque characteristics for different filling levels FG 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. 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.
13 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. 13/5 Siemens MD 10.1 · 2015 FG = 80% FG = 75% FG = 70% FG = 65% FG = 60% FG = 55% Speed n 2 S NS S N N