With the differential valve setting outlined above, it is apparent that as long as the ship is operated below the pressure height of the forward ballonet, air is re› leased only from this ballonet when the altitude of the ship is increased. Hence, if upon descending, the pilot operates only the forward damper, the air which has been valved out during the ascent will be replaced to the for› ward ballonet, thus restoring the trim of the ship to the same condition that exis ted at take-off. 

During short flights, the opera tion of the system is automatic, and no manual adjustment needs to be made except to open the forward damper. During long flights, occasional manual adjustments of the air balance may be necessary, but the system remains largely self-operating. 

(d) Air Valve Adjustment 

All valves are adjusted to their specified settings and t ested before being installed in the airship and re› tested after installation. 

The valve settings should not be changed unless diffi› culties arise. Adjustments should then be made only by a qualified person. During emergency, it may be necessary to adjust the valve in flight. Instructions below should clarify any difficulties that may be encountered. 

