fully  and  record  pressure  on  the  gauge  located below the clapper at the lowest point. Close the 2-inch  drain  valve  and  record  pressure  at  the stabilization   point.   Notice   whether   pressure returns quickly or slowly. Maintain a continuous record of drain tests. If recorded pressure when the  valve  is  wide  open  is  similar  to  previous recordings  and  pressure  returns  quickly,  it  is normal. If  recorded  pressure  when  the  valve  is  wide open is significantly lower or pressure is slow to return when the valve is closed, there may be an obstruction  in  the  waterway.  Check  for  the following   problems: . Partially closed valves to sprinkler system .  Obstruction  in  alarm  valve  preventing clapper  from  opening  freely Test  local  water-flow  alarm  operation  monthly by   opening   the   test   connection   at   the   end of  the  system.  Where  there  is  no  test  con- nection,  the  alarm  may  be  tested  by  opening the  bypass  valve  to  the  circuit  opener  or  closer or  by  opening  the  2-inch  drain  valve  about two   and   one-half   turns.   Do   not   test   water motor  alarms  during  freezing  weather.  To  find principal  causes  of  alarm  failures,  check  for  the following: .   Failure   of   automatic   drain   on   retard chamber  to  close .  Closed  or  partially  closed  valve  on  piping to  alarm  devices .  Plugging  of  bell  casings  of  water  motor gongs  by  foreign  material l  Corrosion  of  moving  parts  of  water  motor gongs . Detachment of shaft couplings from water motor   gongs .  Insufficient  water  flow  to  operate  devices .  Alarm  check  valve  corroded  shut  (this failure  is  not  common  and  will  not  occur  when systems are properly maintained) 8-21 To find principal causes of false fire alarms, check  for  the  following: . Improper drainage of retard chamber (cor- rect this by opening the chamber and cleaning or repairing  the  automatic  drain) .  Pressure  surges  through  the  alarm  check valve Fill  wet  pipe  sprinkler  systems  slowly  through throttled valves and open the control valve wide after the system has been filled. Be sure there is no  drainage  from  retard  chambers.  Leakage means  that  the  alarm  valve  clappers  are  not seating  properly.  They  require  cleaning  and possibly  overhauling. Make  internal  inspections  of  alarm  valves when  normal  testing  procedures  indicate  the  need. l l l l Examine  valve  body  for  tuberculation. Check   clapper   operation—the   clapper should  move  freely  without  sticking  or binding. Replace  clapper  facings  as  required. Resurface seat rings as required. Dry Pipe Valves and Air Check Valves Air  check  valves  are  special,  small,  dry  pipe valves  that  are  usually  connected  to  a  wet  pipe system. The alarms are actuated at the wet pipe system riser when the air check valve “trips.” To prevent  premature  operation,  the  valves  should be fitted with an air chamber to maintain at least 50 gallons of air in the chamber and on the system. Perform  the  2-inch  drain  test  quarterly  by opening  the  2-inch  drain  valve  fully  and  recording the pressure at the lowest point. Close the 2-inch drain valve and record the pressure at the stabiliza- tion  point.  Notice  whether  pressure  returns quickly  or  slowly.  Maintain  a  continuous  record of  drain  tests. If the recorded pressure when the valve is wide open is similar to previous recordings and pressure returns  quickly,  it  is  normal. If  recorded  pressure  when  the  valve  is  wide open is significantly lower or pressure is slow to return when the valve is closed, there may be an obstruction in the waterway. Check for partially closed  valves  to  the  sprinkler  system.