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T–50 •   Design with large pulleys with more teeth in mesh. •   Keep belts tight, and control tension closely. •   Design frame/shafting to be rigid under load. •   Use high quality machined pulleys to minimize radial runout and lateral wobble. SECTION 10    BELT TENSIONING 10.1   What Is Proper Installation Tension One of the benefits of small synchronous belt drives is lower belt pre-tensioning in comparison to  comparable  V-belt  drives,  but  proper  installation  tension  is  still  important  in  achieving  the  best possible drive performance.  In general terms, belt pre-tensioning is needed for proper belt/pulley meshing to prevent belt ratcheting under peak loading, to compensate for initial belt tension decay, and to prestress the drive framework.  The amount of installation tension that is actually needed is influenced by the type of application as well as the system design.  Some general examples of this are as follows: Motion Transfer Drives:  Motion transfer drives, by definition, are required to carry extremely light torque loads.  In these applications, belt installation tension is needed only to cause the belt to conform  to  and  mesh  properly  with  the  pulleys.    The  amount  of  tension  necessary  for  this  is referred to as the minimum tension (Tst).  Minimum tensions, on a per span basis, are included in Table 19, on page T-51.  Some motion transfer drives carry very little torque, but have a need for accurate  registration  requirements.    These  systems  may  require  additional  static  (or  installation) tension in order to minimize registration error. Normal Power Transmission Drives:  Normal power transmission drives should be designed in accordance with published torque ratings and a reasonable service factor (between 1.5 and 2.0). In these applications, belt installation tension is needed to allow the belt to maintain a proper fit with the  pulleys  while  under  load,  and  to  prevent  belt  ratcheting  under  peak  loads.    For  these  drives, proper installation tension can be determined using two different approaches.  If torque loads are known  and  well  defined,  and  an  accurate  tension  value  is  desired,  Equation  (10-1)  or  Equation (10-2) should be used.  If the torque loads are not as well defined, and a quick value is desired for use as a starting point, values from Table 20 can be used.  All static tension values are on a per span basis. 0.812 DQ Tst = –––––––– + mS2       (lb)     (10-1)       d (For drives with a Service Factor of 1.3 or greater) 1.05 DQ Tst = –––––––– + mS2       (lb)      (10-2)       d (For drives with a Service Factor less than 1.3) where: Tst =  Static tension per span (lbs) DQ   =  Driver design torque (lbin) d =  Driver pitch diameter (in) S =  Belt speed/1000 (ft/min) where  Belt speed = (Driver pitch diameter x Driver rpm)/3.82 m =  Mass factor from Table 19