V-belt drives may used where a drive efficiency of approximately 95 percent
and a moderate amount of maintenance and replacement is acceptable.
Application. Variable- or two-speed drives should be used when
they will increase overall plant efficiencies and save money. Generally
variable speed drives on fans over 10 HP (7.46 kW) and boiler feed pumps, over
7 1/2 HP (5.6 kW) will be cost effective. The benefits of variable speed
Reduced starting current,
Longer pump seal life,
Reduced impeller wear (on induced draft fans),
Higher system efficiency,
Less vibration and noise.
The following should be considered when specifying
variable speed drives.
Variation of load, minimum to maximum,
Speed variation required for maximum to minimum service,
c) Overall efficiency of the train of components selected over the
range of the load,
Initial cost of drive versus potential savings.