Variable Pitch Pulley And Belt Tension - Braemar RPA Series Installation, Operation & Service Manual

Variable Pitch Pulley and Belt Tension.

Models RPA400 - 900 are fitted with a variable pitch pulley so that the full potential of the motor
can be utilised. The pulley is set at the factory to approximate the full motor load with the unit at
free delivery. When installed and operating against system resistance, (with doors and windows
open) adjustment may be made to the pulley in order that all the available power is utilised.
Models RPA1000 - RPA1300 are supplied with variable pitch pulleys. Fixed pulleys are fitted to
the RPA1400 - RPA1800.
 Method of Variable Pulley Adjustment.
1. Ensure installation is complete and that all registers are set to their maximum openings.
2. Operate the unit and allow the motor to warm up ( 10 - 15 minutes ).
3. Measure the current being drawn by the motor on high speed.
4. Compare the rated current shown on the rating plate, to the measured current. If the current is
significantly above or below the rated current, pulley adjustment may be made as follows.
5. Isolate unit and remove the " V " belt/s. Loosen the grub screws in the flange of the pulley.
Screw pulley flange in to increase the blower speed and amperage, and screw it out to
decrease blower speed and amperage.
Re-tighten the grub screws in the flange evenly.
6. Adjust the pulley as shown in figure below.
7. It will be necessary to adjust the belt tension by using the jacking screws after any pulley
adjustment has been made.
8. A new drive can be tightened initially 50% more than normal to allow for the drop in tension
during run-in.
Motor / Pulley arrangement for models RPA400 TO RPA600
MOTOR
BELT TENSION SCREW
RPA INDUSTRIAL AIR CONDITIONERS
PULLEY
1.6mm/100mm SPAN @ 2.0kg
BELT DEFLECTION FORCE
If turning pulley counter clockwise to reduce

blower speed, ensure that the V section is not
opened far enough to allow the belt to ride on
the threaded part of pulley, as this will cause
damage to the belt.
 Too great a belt tension will increase
motor load, and shorten belt and bearing
life.
Too loose a belt will cause belt slippage
and excessive belt and pulley wear.