AIR COMPRESSOR - MIDLAND BRAKE MODELS EL-1300, EL-1600 All  valves  and  unloader  components  are  installed  within the cylinder head.  The inlet and exhaust valve discs are spring-loaded against seats installed In the bottom of the head.  The unloader mechanism is installed from the top of the head. The   compressor   governor   is   mounted   directly   to   the cylinder  head  or  can  be  remotely  mounted.    The  gover- nor  controls  the  minimum  and  maximum  air  pressure supplied by the compressor. OPERATION COMPRESSION With the down stroke of each piston, air Is drawn Into the cylinder  through  a  disc-type  Inlet  valve  in  the  cylinder head.  As the pistons begin the upward  stroke,  the  inlet valve closes and the trapped air above the piston is then compressed.      When   the   air   pressure   in   the   cylinder becomes  greater  than  the  air  pressure  in  the  cylinder head above the exhaust valve, the exhaust valve is then forced  open  off  its  seat.    Air  is  then  allowed  to  pass through  the  exhaust  port  into  the  head  cavity,  and  from there into the line leading to the air reservoir.  When the piston   starts   its   downward   stroke,   the   exhaust   valve returns to its valve seat and the compressed air  will  not return to the cylinder.  The intake and compression cycle Is then repeated. UNLOADING (NOT COMPRESSING) When air pressure in the system reaches the maximum governor pressure setting, the governor is actuated causing the unloader pins to hold the inlet valves off their seats  (open).    With  the  inlet  valves  open,  air  passes freely back and forth between the cylinder bores and the intake  cavity  in  the  cylinder  head.    This  suspends  the compression  of  air  until  the  pressure  in  the  system  Is reduced  to  the  governor  cut-in  setting.    The  governor then     exhausts     the     air     pressure     to the unloader mechanism, releasing the unloader pins.  This allows the inlet valves to function normally and the resumption of air compression. MAINTENANCE Air  filters  should  be  cleaned  or  replaced  when  the  vac- uum   level   exceeds   508.0mm   (20   Inches)   of   water   at compression.  The governor settings and unloader oper- ation  should  be  checked  regularly.    Maximum  desirable reservoir pressure is 826 + 27.6 kPa (125 + 5 psi). Type of  air  cleaner,  operating  conditions  and  experience  may dictate additional service activity. Check  compressor  mounting  to  be  sure  it  is  tight.    Be sure  the  drive  pulleys  are  in  proper  alignment  and  belt tension  is  properly  adjusted.    Make  sure  the  oil  supply and coolant lines are in good condition and not restricted. If  the  air  compressor  should  fail  to  maintain  sufficient pressure  or  supply  excessive  air  pressure,  the  unloader mechanism pins or seals could be defective. The  unloader  components  can  be  serviced  or  replaced without   removing   the   compressor   from   the   vehicle’s engine. Refer to disassembly procedures for unloader on page 6 and assembly procedures for unloader on page 11. TROUBLESHOOTING GUIDE CONDITION POSSIBLE CAUSE RESOLUTION Compressor fails to maintain Dirty intake cleaner Clean or replace element as sufficient pressure or adequate necessary. air supply. Restriction in compressor Repair or replace as necessary. cylinder head intake, discharge cavities or line. Leaking or broken inlet or Repair or replace valves as exhaust valves necessary. Excessive wear Repair or replace compressor as necessary. Drive belt slipping Adjust or replace belt. Excessive system leakage Check all fittings and connections. Defective governor Repair or replace governor as necessary. Governor with improper setting Adjust governor as necessary. Gauge defective Replace gauge as necessary. CTS-4077Y - Page 4