TM 5-3895-374-24-2 4. When   approaching   an   obstacle   in   the   suction   or discharge line, go around the obstacle instead of over it.    Going  over  it  creates  an  air  Docket.    See  Figure 10. 5. Where  practical,  slope  the  piping  so  no  air  or  liquid pockets will be formed.  Air pockets in the suction line make it hard for the pump to prime. 6. For a suction line with a long horizontal run keep the horizontal  portion  below  the  liquid  level  if  possible. This keeps the pipe full so the pump does not have to remove so much air when starting; this is most helpful when there is no foot valve.  See Figure 11. 7. When   piping   a   hot   or   cold   system   (liquid   being handled   is   at   a   temperature   different   from   the   air surrounding the pump) be sure allowance is made for expansion   and   contraction   of   the   piping.      Loops, expansion  joints,  or  unsecured  (this  does  not  mean unsupported)   runs   should   be   used   so   the   pump casing is not distorted or put into a bind. 8. STRAINER - It is always good practice to consider a strainer on the suction side of a positive displacement pump.    The  strainer  will  keep  foreign  objects  from going  into  the  pump;  without  a  strainer  some  would go  through:    others  would  cause  a  jammed  pump,  a broken  part,  or  a  torn  up  drive.    The  strainer  basket mesh  or  perforation  size  should  be  big  enough  so that it does not cause excessive pressure drop, but it should be find enough to protect the pump.  When in doubt     as     to     the     proper     size,     check     with     the manufacturer,  giving  him  pipe  size,  flow  rate.    and viscosity   involved.      Provision   should   be   made   for cleaning     the strainer. If the pump operates continuously   a   bypass   should   be   built   around   the strainer or two strainers should be put in parallel with proper  valving  so  they  can  be  isolated  for  cleaning. Use of a strainer is particularly important at start up to help clean the system of weld beads, pipe scale.  and other foreign objects.  For additional information, refer to TSM640. 9. If  the  pump  is  not  equipped  with  a  pressure  relief valve consideration should be given to mounting one in  the  discharge  line.    See  discussion  on  pressure relief valves under START UP 10.  The pump should not be used to support the piping.  The weight of the pipe  should  be  carried  by  hangers,  supports  stands, etc. 11. When  fastening  the  piping  to  the  pump  it  should  not be   necessary   to   impose   any   strain   on   the   pump casing.  "Springing"  or  "drawing"  the  piping  up  to  the pump will cause distortion possible misalignment, and probable   rapid   wear   of   the   pump   Do   not   use   the pump to correct errors in piping layout or assembly. FIGURE 11 12. All  joints  of  the  piping  system  should  be  tight;  pipe sealer    or    teflon    tape    will    help    assure    leak-free threaded  joints.    Leaks  in  the  suction  line  permitting air  to  be  drawn  in  may  cause  a  noisy  pump,  or  a reduction in capacity. 13. ALIGNMENT- Check the  alignment  of  the  drive  after the  piping  is  hooked  up.    As  a  final  check  on  pump alignment  remove  the  head  of  the  pump  and  with  a feeler  gauge  determine  if  there  is  clearance  all  the way around between the  rotor  and  casing.    Because of    manufacturing    tolerances,    bushing    clearances, etc., the rotor may not be centered in the casing, but it   should   not   drag:      dragging   would   indicate   unit misalignment  or  casing  distortion  from  piping  strain. Making  this  check  is  most  desirable  on  installations involving Q, M and N size standard duty pumps. 14. The  auxiliary  piping  hooked  to  jackets,  glands,  etc. for heating, cooling, quenching, or for other purposes should   receive   the   same   attention   as   the   piping handling the liquid pumped. 15. Provide a pressure relief device in any part of a pump and  piping  system  that  can  be  valved  off  and,  thus, completely isolated.  This is particularly important: 1. When handling a cold liquid such as refrigeration   ammonia   that   can   warm   up   to ambient  temperatures  when  the  pump  is  shut off or 2. When   handling   a   liquid   such   as   asphalt   or molasses  that  has  to  be  heated  before  it  can be  pumped.    The  rise  in  temperature  causes the liquid to expand; if there is no provision for pressure  relief  in  the  closed  off  section,  there is    a    chance    that    the    pump    or    piping    will rupture. START UP Before pushing the "start" button, check the following: 1. Are  there  vacuum  and  pressure  gauges  on  or  near the pump? These gauges are the quickest and  most accurate way of finding out  what  is  happening  in  the pump. Page 3 - 1205