3. Low-Pressure System

3.1 Check initial status of low-pressure system

  • All vaporizers correctly installed
    • Vaporizers are full and fill ports closed
    • Tops of vaporizers are parallel to manifold - cannot be lifted off manifold
    • Only one vaporizer turns ON at a time


  • overfilling of vaporizer
  • vaporizer not locked on to manifold
  • faulty interlock mechanism - can turn on two vaporizers simultaneously
  • vaporizer will not turn ON - interlock obstructed by ECG lead, etc

3.2 Perform low-pressure leak test

  • Verify master switch OFF, vaporizers OFF
  • Do leak test with "suction bulb" device on common (fresh) gas outlet
    • Verify bulb stays collapsed for > 10 secs


  • defective suction bulb
  • leak somewhere between flow control valves and common gas outlet
  • cracked, loose, misaligned flow tubes
  • loose connections - piping, components
  • Repeat leak test for each vaporizer, one at a time - setting dial to 1% conc.
  • partially open filler/drain port
  • missing port O-ring on manifold
  • Verify all vaporizers OFF, fresh gas hose reconnected, and flush system with O2

3.3 Turn ON gas machine master switch

  • O2 supply failure alarm activated
  • Electrical mains light activated and battery fully charged


  • alarm mechanism malfunction
  • battery discharged because machine left ON and unplugged to AC outlet

3.4 Test flowmeters

  • Minimum flows are 20025 ml/min for O2 and zero ml/min for other gases
  • no flow - broken tip of needle valve
  • Flowtubes are undamaged; floats move smoothly throughout their full range
  • floats sticking - dirt, grease, static
  • float stuck at top of flow tube
  • stop broken off from top of flow tube and resting on float
  • You cannot set the O2 and N2O flow controls to supply hypoxic flowrates
  • N2O/O2 3:1 proportioner - linkage broken or gear stop misaligned
  • Low O2 pressure stops other gas flows
    • Set floats to mid-range - disconnect O2 pipeline - push O2 flush
    • O2 supply failure alarm sounds and Air and N2O floats drop
  • no low O2 supply alarm at 30 psig
  • shutoff valves fail to close at 20 psig
  • Turning ON vaporizer does not lower gas flow
  • obstruction in vaporizer or manifold

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