TM 5-3895-374-24-2 be direct coupled to a driving motor, consider the height of the motor   shaft    and    the    necessity    for    it    to    be    aligned    very accurately with the blower shaft.   Best  arrangement  is  for  the blower  to  be  bolted  directly  to  the  mounting  plate  while  the driver is on shims of at least 1/8 inch (3 mm) thickness.  This allows adjustment of motor position in final shaft alignment by varying the shim thickness. Satisfactory   installation   can   be   obtained   by   setting   the baseplate on a concrete slab that is rigid and free of vibration. and leveling the top  of  the  base  carefully  in  two  directions  so that it is free of twist.  The slab must be provided with suitable anchor bolts.  The use of grouting under and inside the base, after     it     has     been     carefully     leveled     by     shimming.          is recommended. When blower and driver have been factory mounted on a common   baseplate.      the   assembly   will   have   been   properly aligned and is to be treated as a unit for leveling purposes.  It is  possible  for  a  base  mounted  assembly  to  become  twisted during  shipment  thus  disturbing  the  original  alignment.    For this   reason,   make   the   following   checks   after   the   base   has been leveled and bolted down. Disconnect the drive and rotate the blower shaft by hand. It should turn freely at all points.  Loosen the blower foot hold- down   screws   and   determine   whether   all   feet   are   evenly   in contact  with  the  base.    If  not.    insert  shims  as  required  and again  check  for   free   impeller   rotation.      Finally,   if   blower   is direct    coupled    to    the    driver,    check    shaft    and    coupling alignment carefully and make any necessary corrections prior to grouting. In   planning   the   installation,   and   before   setting   the   blower, consider how piping  arrangements  are  dictated  by  the  blower design and assembly. When a blower is DIRECT COUPLED to its driver. the  driver  RPM  must  be  selected  or  governed  so  as  not  to exceed  the  maximum  speed  rating  of  the  blower.    Refer  to LIMITATIONS for allowable speeds for various blower sizes.  A flexible  type  coupling  should  always  be  used  to  connect  the driver and blower shafts. For   engine   drives,   couplings   with   proper   stiffness   must   be selected to avoid resonant torsional vibrations. Also,  safe  operating  speed  must  be  limited  to  avoid  critical speeds. Coupling  halves  must  be  accurately  aligned,  and  a  sufficient gap between shaft ends provided, so that side strains and end thrust   on   either   shaft   are   avoided   or   minimized.      This   will require  considerable  care  in  the  mounting  of  the  driver.    The two    shafts    must    be    in    as    near    perfect    alignment    in    all directions  as  possible,  and  the  gap  must  be  established  with the  motor  armature  on  its  electrical  center  if  end  play  exists. Coupling halves must be fitted to the two shafts such that they can  be  worked  into  place  by  hand.    Maximum  deviation  in offset  alignment  of  the  shafts  should  not  exceed  .005"  (.13 mm)  total  indicator  reading,  taken  on  the  two  coupling  hubs. Maximum  deviation  from  parallel  of  the  inside  coupling  faces should not exceed .001" (.03 mm) when checked at six points around the coupling. CAUTION Couplings  as  well  as  sheave  bushings  must  have  a slight slide fit with the blower shaft such that they can be installed in place by hand.  Any force used to install them will   change   blower   end   clearances   resulting   in   blower damage.  If an interference fit is desired for the coupling, the  coupling  hub  should  be  heated  and  shrunk  on  the shaft.      For   engine   drives,   use   "Locktite"   between   the coupling  hubs  and  the  blower/engine  shafts  and  on  the threads of the coupling set screws. When a blower is BELT DRIVEN.  a proper selection of sheave   diameters   can   usually   be   made   to   adapt   any standard driver speed to the required blower speed.  This flexibility  can  sometimes  lead  to  operating  temperature problems  caused  by  blower  speed  being  too  low.    Make sure   the   drive   speed   selected   is   within   the   allowable range   for   the   specific   blower   size,   as   specified   under LIMITATIONS. Belted drive arrangements usually employ two or more V- belts  running  in  grooved  sheaves,  and  a  variety  of  positions are  available  for  the  driver.    Installation  of  the  driver  is  less critical than for direct coupling, but its shaft must be level and parallel   with   the   blower   shaft.      The   driver   must   also   be mounted  on  an  adjustable  base  to  permit  installing,  adjusting and  removing  the  V-belts.    To  position  the  driver  correctly, both  sheaves  need  to  be  mounted  on  their  shafts  and  the nominal shaft center distance known for the belt lengths to be used. Install  the  blower  sheave  (usually  the  larger  onel  so  that its  inner  hub  face  is  not  more  than  %4  inch  (7  mm)  from  the bearing   end   cover.      The   shaft   fit   should   be   such   that   the sheave can be worked into place by hand.  A tight or driving fit can    damage    a    bearing,    and    may    cause    internal    blower damage  by  forcing  the  impeller  out  of  its  normal   operating position.  A loose fit or wobbly sheave will cause vibration, and may result in shaft breakage. The driver sheave should also be mounted as close to its bearing  as  possible,  and  again  should  fit  the  shaft  correctly. Position  the  driver  on  its  adjustable  base  so  that  2:1  of  the total   movement   is   available   in   the   direction   away   from   the blower, and mount the assembly so that the face of the sheave is  accurately  in  line  with  the  blower  sheave.    This  position minimizes belt wear.  and allows sufficient adjustment for both installing  and  tightening  the  belts.    After  belts  are  installed, adjust   their   tension   in   accordance   with   the   manufacturer’s instructions.  However, only enough tension should be applied to  prevent  slippage  when  the  blower  is  operating  under  load. Excessive tightening can lead to early bearing failures. Failure to properly align the blower and drive sheaves will result    in    the    impeller    being    forced    against    one    of    the headplates  during  operation  causing  serious  damage  to  the blower. In   the   absence   of   belt   manufacturer’s   instructions   for tensioning.  the following procedures may be used. 1. With the belts loose.   pull  the  slack  on  all  of  them  to  the bottom side of the drive. 2. Adjust motor position to tighten belt until they appear to be seating in the sheave grooves. 3. Thump  the  belts  with  your  fist.    If  they  feel  dead,  tighten them more until they vibrate and feel springy when struck. 4. Run-in  the  drive  for  a  short  period,  after  preparing  the blower   as   instructed   in   a   following   paragraph.      While running, adjust until only a very slight bow appears in the slack side of the belts. 5. Stop the motor and compare the tensions of the individual belts  by  pressing  down  firmly  with  one  hand  on  the  top surface.  It should be possible to deflect each page 3-805