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2-8 TM 55-4929-400-13 2-36. Testing Radio Interference Suppression. a. Place a radio receiver that is in good operating condition in a position not more than 5 feet from the tester. A wide band receiver with a frequency range of 0.15 to 1000.0 megacycles is preferred. b. Start  the  tester  and  tune  the  receiver  in  to three  widely  separated  frequencies  at  maximum volume.  Use  frequencies  that  are  free  of  signals with  strong  carriers  so  that  the  receiver  will  be  in its  most  sensitive  operating  condition. c. When the tester is operating, listen to the re- ceiver for interference which ceases when the tester is stopped and which indicates that the suppression is defective. 2-37. Replacement of Suppression Component. a.  Removal. (1)  Disconnect  plug  from  receptacle. (2) Cut lockwire and remove from screws. (3)  Remove  screws  securing  filter  to  electric motor and remove filter and gasket from motor. b.   Installation. (1)  Place  gasket  and  filter  in  position  on motor and secure with screws. (2) Secure the top two screws together and the bottom two screws together with the lockwire. (3) Install the plug on the receptacle. Section VII. PNEUMATIC  SYSTEM 2-38.  General.  The  pump  serves  the  dual  func- tion  of  developing  pressure  as  well  as  vacuum  for operation  of  the  tester.  In  the  pressure  section,  a mixture of air and oil is pumped into the reservoir where the oil and air are separated. The separated oil  drops to the bottom of the reservoir where it is fed  to  the  pump  for  lubrication  purposes,  the  air being  forced  out  at  the  top  of  the  reservoir  under pressure.  The  pressurized  air,  after  going  through the  check  valve  whose  function  is  to  prevent  oil from  entering  instrument  lines  during  operation, enters  an  oil  sump  and  passes  through  a  filter  which is an integral part of the sump. Air from the sump flows  through  two  pressure  control  valves.  The  pres- sure  INCREASE  valve  controls  the  amount  of  air permitted   in   the   system   and   the   pressure   DE- CREASE valve opens the line to the ambient air, al- lowing  system  pressure  to  bleed  off.  The  available pressure level, as fixed by the control valves is sent to the pressure relief valve and PRESSURE selector valve. Setting the PRESSURE selector valve at the desired test position completes the circuit to the in- strument  under  test  and  simultaneously  connects the  instrument  under  test  and  the  master  instru- ment to one of the pressure relief valves. The pres- sure relief valve is in the line at all times and pro- tects the instruments from pressure overload when the   pump   is   producing   vacuum   which   passes through the check valve, and the sump which pre- vents  oil  from  entering  the  instrument  lines.  The vacuum  INCREASE  valve  controls  the  amount  of vacum in the system and the vacuum DECREASE valve opens the line to the ambient air allowing the system vacuum to bleed off. Setting the VACUUM selector valve at the desired test position completes the  circuit  to  the  instrument  under  test  and  the master instrument to one of the three relief valves which  protect  the  instruments  from  vacuum  over- loads. The case leak valves provide isolation for the master  instruments  of  the  test  set  to  permit  case leak  tests  and/or  calibration  of  the  master  instru- ments without removing them from the tester. 2-39. Adjustment of Safety Relief System.  All instruments are protected by a safety relief system which  operates  if  excessive  pressure  or  vacuum  is applied to any instrument. Five bellows assemblies are  used,  two  for  vacuum  and  three  for  pressure  (fig. 2-2). If excessive pressure or vacuum occurs, the ap- plicable bellows actuate an associated microswitch which in turn applies operating power to two sole- noid valves. One valve is located in the pump pres- sure  line  and  one  is  located  in  the  vacuum  line. When  the  valve  operates,  the  pressure  and  return lines   close   to   isolate   the   instruments   from   the pump.  This  safety  relief  system  has  been  properly set at the factory. In the event minor adjustment of the safety relief system is required, proceed as fol- lows. a.  Prepare  test  set  for  use  in  accordance  with procedure given in paragraph 2-25. b. Release 10 captive fasteners and remove bot- tom front panel of test-set to gain access to bellows block assembly. c. Place  appropriate  instrument  under  vacuum or pressure, depending upon which bellows is to be adjusted. Refer to paragraph 2-26 for operating pro- cedure. Adjust the test set until instrument shows maximum  indication. d. Refer to figure 2-2 to identify bellows to be ad- justed; markings on front of bellows block assembly identify each bellows assembly and the instrument system  which  it  protects.  Refer  to  table  2-1  for safety relief point settings.

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