TM 5-3895-374-24-2 adjusting  screw  (D).    The  pump  discharge  pressure  pushes against  the  under  side  of  the  poppet  at  point  (E).    When  the force   exerted   by   the   liquid   under   the   poppet   exceeds   that exerted by the spring.  the poppet lifts and liquid starts to flow through the valve.  As the discharge pressure builds up more and   more   of   the   liquid   flows   through   until   a   pressure   is reached   at   which   all   of   the   liquid   being   pumped   is   going through the valve This pressure is the relief valve setting. CAUTION THE INTERNAL TYPE PRESSURE RELIED CALVE MOUNTED ON THE VIKING PUMP SHOULD   ALWAYS   HAVE   THE   CAP   OR BONNET POINTED TOWARD THE SUCTION    SIDE    OF    THE    PUMP.        THE RETURN-TO-TANK TYPE PRESSURE RELIED    VALVE    SHOULD    ALWAYS    BE MOUNTED ON THE DISCHARGE SIDE OF THE    PUMP.        IF    PUMP    ROTATION    IS PERMANENTLY  REVERSD  CHANGE  THE RELIEF   CALVE.      TURN   THE   INTERNAL TYPE     END     FOR     END     ;     MOVE     THE RETURN-TO-TANK TYPE  TO  THE  OTHER PORT. IF, ON A PARTICULAR INSTALLATION IT IS INTENT TO REVERSE THE PUMP ROTATION FREQUENTLY,   e.g.,   USING   ONE   PUMP TO FILL A TANK AND THEN BY USE OF A REVERSING  SWITCH  OR  OTHER  MEANS CHANGING   ROTATION   TO   PERMIT   THE SAME PUMP TO CIRCULATE THE LIQUID THROUGH A HEATER OR TO LOAD OUT) THEN    OVER    PRESSURE    PROTECTION MUST  BE  PROVIDED  FOR  BOTH  SIDES OF THE PUMP OR FOR BOTH ROTATIONS. USE AN INTERNAL PRESSURE RELIEF VALVE TO PROTECT ONE   SIDE   AND   AN   IN-LINE   PRESSURE RELIEF VALVE TO PROTECT THE OTHER;    USE    AN     IN-LINE     PRESSURE RELIEF  VALVE  ON  EACH  SIDE  OF  THE PUMP OR USE SOME MEANS OF LIMITING TORQUE THAT IS FUNCTIONAL IN BOTH DIRECTIONS OF ROTATION. Viking pumps can be furnished with either an internal pressure relief valve - one which directs the flow from the valves back to the suction side of the pump - or a return-to-tank valve which directs the flow through piping back to supply tank.  See figure 5.    An  inline  pressure  relief  valve  mounted  in  the  discharge piping also directs the flow back to the supply tank.  This type of  valve  should  be  mounted  close  to  the  pump  so  that  the pressure  drop  though  the  piping  between  the  pump  and  the valve is at the minimum.  Be sure there are no shutoff valves between  the  pump  and  relief  valve.    Piping  from  a  return-to- tank  or  an  in-line  valve  to  the  supply  tank  should  also  be  as short and large as possible. The  spring  loaded  poppet-type  valve  is  strictly  a  differential valve,   sensing   only   those   pressures   on   each   side   of   the poppet.    It  should  not  be  used  as  a  pressure  or  flow  control device.  It is intended strictly as a pressure relief valve. The   pressure   at   which   either   the   return-to-tank   or   internal pressure relief valve bypasses can be changed by turning the adjusting screw.  Do not back the adjusting screw all the way out. NOTE on some models the pressure relief valve is  mounted  on  the  pump  casing  instead of the pump head. Stop when spring tension is off the screw (the screw starts to turn easily). For  details  on  maintenance  of  the  relief  valve  see  Technical Service Manual covering your model series. 6. Motor - follow local electrical codes when hooking up motors. Foundation Every  pump  should  have  a  good  foundation.    It  may  be  any structure   sufficiently   strong   to   hold   the   pump   rigid   and   to absorb any strain or shock that may be encountered. A   certified   print   of   the   pumping   unit   should   be   used   in preparing the foundation.  As for one.  If a separate foundation is provided.  make it at least four inches wider and longer than the base of the unit. When the unit is placed on the foundation it should be leveled and  checked  for  position  against  the  piping  layout  and  then fastened down. Page 3 - 1203