Mechanical Engineering

The most important operational and maintenance issue in a V-belt drive is its tension. Ifbelts are too loose, they tend to vibrate, wear rapidly, and waste energy through slippage.If belts are overtightened, they will show excessive wear. An increased belt load mayshorten bearing life through excessive lateral loading and could possibly result in shaftfailure. The proper tension of a V-belt is the lowest tension at which the belt will not slipat peak-load conditions. After the break-in period, belt tension should be checked every3 to 6 months.A notched belt has grooves or notches that run perpendicular to the belt's length, whichreduces the bending resistance of the belt. Notched belts can use the same pulleys ascross-section standard V-belts. They run cooler, last longer, and are about 2% moreefficient than standard V-belts.Synchronous belts (also called cogged, timing, positive-drive, or high-torque drivebelts) are toothed and require the installation of mating grooved sprockets. These beltsoperate with a consistent efficiency of 98% and maintain their efficiency over a wideload range.2 In contrast, V-belts have a sharp reduction in efficiency at high torque dueto increased slippage. Synchronous belts require minimal maintenance and retensioning,operate in wet and oily environments, and run slip-free. However, synchronous belts arenoisier than V-belts, less suited for use on shock-loaded applications, and transfer morevibration due to their stiffness.

Example Energy

Example Energy Savings Calculations
A continuously operating, 100-horsepower (hp), supply-air fan operates at an average
motor load of 75% while consuming 527,000 kilowatt-hours (kWh) of electrical energy
annually. What are the annual energy and dollar savings if a 95% efficient (η1) V-belt is
replaced with a 98% efficient (η2) synchronous belt? Electricity is priced at $0.08/kWh.
Energy Savings = Annual Energy Use x (1 - η1/η2 )
= 527,000 kWh/year x (1 - 95/98) = 16,130 kWh/year
Annual Cost Savings = 16,130 kWh x $0.08/kWh = $1,290
Suggested Actions
■■ Conduct a survey of belt-driven
equipment. Gather application and operating-hour data. Then
determine the cost effectiveness
of replacing existing V-belts with
notched belts or synchronous
belts and sprockets.
■■ Consider synchronous belts for all new installations; the price
premium is minimal due to the
avoidance of conventional
pulley costs.
■■ Consider having a power
transmission specialist determine
the energy and cost savings
potential from retrofitting all
V-belt drives with synchronous
belts. Synchronous belts rely on
tooth grip instead of friction to
efficiently transfer power and
provide a constant speed ratio.
■■ Install notched belts where the
retrofit of a synchronous belt is
not cost effective.

Energy Tips: MOTOR SYSTEMS Motor Systems Tip Sheet #5

Mirza M Saleem

Engineering Manager

TransAsia Refinery

Karachi