Fluid coupling

Power for each Hquid and the soHd phase must be added to get Pp. P, the soHds process power, = T -AN for scroU decanters, where = conveyor torque and AN = differential speed between bowl and conveyor. Pp is the friction power, ie, loss in bearings, seals, gears, belts, and fluid couplings. P, the windage power, = K and fi = viscosity of surrounding gas p = density of gas D = rotor outside diameter N = rpm and K = shape... 

Speed variation through variable-speed fluid couplings... 

Table 6.5 Comparative study of performance of an a.c. drive, variable speed fluid coupling and a d.c. drive...

Features A.C. drive Variable Speed fluid coupling D.C. drive ... 

Figure 6.52 An approximate iliustration of p and loss variation, with change in speed in a variable-speed fluid coupling...

Variable drive fluid couplings (see Section 8.4.1(2)) These may not prove to be as effective from the point of view of energy conservation, as the motor will always be running at its rated speed and engagement of the coupling alone will vary the output speed. 

The use of a squirrel cage motor is, however, inevitable as discussed earlier particularly for a process plant or a power house application, where downtime for maintenance of a slip-ring motor is unwelcome, or a chemical plant or contaminated locations, where the application of a slipring motor is prohibitive. To meet such load requirements with a squirrel cage motor, the use of fluid couplings to start the motor lightly and reduce starting time, is quite common and economical, as discussed in Chapter 8, and must be adopted in the above case. 

Let us use a fluid coupling and start the motor lightly, similar to Figure 8.3. The revised accelerating torque and approximate clutching sequence of the coupling is illustrated in Figure 7.22. 

Figure 8.4 Constant filled fluid couplings (Courtesy Fluidomat Ltd)...

Fluid couplings have a proven record of reliability and ease of operation. They thus have found wide application wherever a light load start and capticily control of drives is required as in fans and pumps. 

I It is possible to switch the motor at no load by selecting a variable-speed fluid coupling. The oil need not be pretilled which can be varied at site during operation as required. 

Figure 8.7(a) Variable-speed scoop control fluid coupling (Courtesy Fluidomat)... 

This is as for fluid couplings but at lower ratings. Generally, they are used in the cement, rubber and chemical, paper, chemical fibre, electric wire making and mining industries, as well as in material handling, conveyors and thermal pow er plants. 

Figure 8.8 Illustration of clutching of a scoop control variable fluid coupling...

Soft slarlers, star-delta, wound motor and A/T starters, or when the prime mover is fitted with centrifugal dutches or delayed-action fluid couplings... 

There is special coverage of fluid couplings for soft starting and speed control, A comparison between static drives and variable-speed fluid couplings is inade. 

The torque converter soon replaced the fluid coupling as the hydrodynamic device of choice in the automatic transmission. A schematic of a simple... 

The distinguishing performance characteristic of the torque converter, in contrast to the fluid coupling, is that It IS capable of multiplying torque. Torque multiplication is made possible by vane curvature and the presence of the reactor. When the converter is stalled—that is, the turbine and the reactor are stationary—the torque delivered to the gearbox is typically 2... 

Two-speed electric motor with belts or gears, gear or fluid coupling. 

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