(b) Damper Control  (c) Manometers  The air dampers can be kept open by means of an  olive on the control cables.  The dampers are normally  held closed by springs which prevent the dampers from  opening under the pressure of air from the scoops.  The air pressure in the two ballonets and the gas  pressure in the envelope are read on three manometers,  located on the flight panel.  Each manometer is equipped  with a three-position valve•.  When this valve is turned on the position marked  "Check" the manometers should read zero.  If necessary,  the reading can be brought back to zero by means of an  adjusting dial.  This check should be made before every  take-off.  v7hile in flight the valve should be turned on the  position marked "static."  A  mechanical manometer on the instrument panel reads  the gas pressure and is used as a check .on tl).e liquid  manometer.  -43-