partments and six pressure-resistant alumi- 

 num spheres were located in the center por- 

 tion of the vehicle. A high-pressure gear 

 pump pumped automatic transmission fluid 

 from the spheres to the flexible containers 

 (Fig. 6.4). Air at atmospheric pressure filled 

 the spheres when emptied of working fluid. 

 Since the flexible containers were exposed to 

 sea pressure, the pump had to move the 



working fluid against sea pressure. A revers- 

 ible DC motor provided power for the pump. 

 To control the system, a positive-seating 

 (leak-free) ball valve was incorporated into 

 the circuit. The ball valve was opened and 

 closed by a suitable gear train and electric 

 motor. The two motors were under the direct 

 control of the pilot who could control the 

 buoyancy of the vehicle from a heavy condi- 



VARIABLE BALLAST SPHERES 



FILL- 

 BLEED 



VARIABLE BALLAST BAGS 



Fig. 6.4 ALVIN's variable-ballast system diagram. [From Ref. (5)1 



293 



