the cabin ceiling, starboard, and makes a  nyn  connection  with the helium inflation sleeve.  Only the amount of air  necessary to bring the pressure to  th~  required value  should be used.  The gas release system includes two 20-inch gas  valves, located on the port and starboard sides of the  envelope at panel 34, and gores K and .L.  It includes, also,  two rip panels located on the top of the ship from panel 21  to 28, and from panel 53 to 59.  The gas valves are set to operate automatically when  the gas pressure reaches 2-1/2-inches of water as read  on the gas manometer.  They can also be operated manually  from the pilot’s instrument panel.  The gas valves are  equipped with micro switches which operate telltale lights  on the pilot’s panel when the gas valve begins to open at  2-1/2-inches of water.  In order to offset localized drop  of pressure in the air stream and to prevent premature  opening of the valves, a semi-circular windshield is attached  to the envelope on the aft side of the. valve.  CAUTION:  Do not attempt to hold gas valves closed  manually when . flying above-pr.essure height  as _excessive pressure maY deYelop in the  envelope.  -39- (3) Gas Release System  (See BuAer Manual 12-304 12-307).  (a) Gas Valves 