Variable speed couplings

Belt drive coupling Chain drive coupling Variable speed drive coupling... 

Options for connecting the motor drive to the shaft depend on the shaft orientation. A vertical-shaft cantilever design would prefer a belt drive to reduce the cost of manufacture of the support structure and to facilitate maintenance. A horizontal shaft has the additional option of direct coupling. Variable speed can be accomplished through a gearbox or preferably through variable frequency control on the motor. In addition to the power requirements discussed previously, the startup power to overcome the torque of the rotor must be considered. This startup power is related to the time required to reach the desired rotor speed. 

Screen drive motor Variable speed coupling... 

Whenever the process machine operates at the same speed as its driver, the two can be directly coupled. This direct couphng stiU allows for a variable speed, through acuustments of the speed or the driver. Steam turbine speed can be easily adjusted, and electric motor speed can also be varied by the use of special drives that vaiw the frequency of the power applied to the motor. Wdiether the speed is fixed or variable, direci coupling of two machine shafts presents the problem of accommodation of misalignment. To this purpose, machines are coupled through a.flexible coupling. 

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...

Figures 8.7(a) and (b) illustrate variable-speed couplings which can provide a stepless speed variation over a wide range. The impeller and runner of the couplings are housed in a stationary housing with a built-in oil sump. Oil is...

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)... 

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. 

Variable speed control Speed change may be achieved by belts, pulleys, gear box sliding couplings, or a variable-speed motor. 

Direct connected, constant or variable speed, belt, gear, fluid coupling. 

Variations in required speed or speed increase or decrease from the driver may be handled by gear boxes, belt or chain drive, magnetic drive, magnetic or fluid couplings, or variable-speed motors. 

Speed variation Variation in speed equates to a corresponding variation in torque. Most variable-speed applications require some type of flexible coupling capable of absorbing these torsional variations. 

Smaller rotary positive displacement compressors are controlled with external bypass. Such equipment usually has a built-in relief valve that opens at a pressure short of damaging the equipment, but the external bypass still is necessary for smooth control. Large units may be equipped with turbine or gas engine drives which are speed adjustable. Variable speed gear boxes or belt drives are not satisfactory. Variable speed dc motors also are not useful as compressor drives. Magnetic clutches and hydraulic couplings are used. 

Figure 7.23. Performances of fans with several kinds of controls (American Standard Co. Inc.), (a) A damper in the duct with constant-speed fan drive, (b) two-speed fan driver, (c) inlet vanes or inlet louvers with a constant-speed fan drive, (d) multiple-step variable-speed fan drive, and (e) hydraulic or electric coupling with constant-speed driver giving wide control over fan speed.

The enzymatic reactor consisted of a 500 mL-continuous tank reactor BIOSTAT Q (Braun-Biotech International) coupled to the ultrafiltration membrane. The additional volume of the ultrafiltration unit and piping was around 150 mL. Three solutions were added to the reactor by means of three variable speed peristaltic pumps, containing (a) Orange II, Mn2+ and oxalic acid (b) H2O2 and (c) MnP. Another peristaltic pump was used in order to feed the effluent into the ultrafiltration unit (Fig. 10.3). The recycling feed flow ratio was maintained at 12 1, as this flow rate allowed an adequate homogeneity of the enzymatic mixture but prevented the polarization or fouling of the membrane. 

Drive motor from 20 to 2000 hp infinitely variable speed drives directly coupled to reducer for maximum efficiency deigned to save floor space. 

Similarly, the uncertainties around the rate controlling step for the slurry reactor may also be dealt with through overdesign of the control system. In that case it may be prudent to provide a couple of control loops that could control the addition of reactant gas through some high-pressure jet spargers or provide a variable speed agitator. 

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