pie, meeting them in practice has consumed 

 a great deal of time and effort. Because oil is 

 used as the pressure compensation medium, 

 all other materials must be oil-compatible. 

 Gasses generated during the batteries' oper- 

 ation must be vented off. As this gas leaves 

 the electrode, it carries entrained electro- 

 lyte, and if no provisions are made to sepa- 

 rate the two (gas from electrolyte), the elec- 

 trolyte may accumulate on top of the cells 

 and elsewhere to produce a host of problems. 

 While the gas may be held in solution at 

 great depths, it leaves the cell or comes out 

 of solution as the vehicle surfaces. These are 

 but a few of the problems associated with 

 pressure-compensation systems. A review of 

 the literature makes one wonder that the 

 system works at all. Nonetheless, it somehow 

 does, and the need to conserve weight and 

 space in deep diving vehicles has prompted a 

 great deal of attention to this procedure. 



The approach to pressure compensation 

 has been on an individual basis; no two sys- 

 tems are precisely the same and all have 

 their own peculiar problems. Consequently, 

 the subject might best be served by concen- 

 trating on the experiences and research of a 

 few, rather than the problems of a multitude. 

 An appreciation for the range through which 

 battery compensation problems can vary 

 from vehicle-to-vehicle can be gained from 

 Figure 7.11. 



The gassing behavior of lead-acid batteries 

 under both atmospheric and high (1,000 psi) 

 pressure conditions was studied in detail by 

 Marriott and Capotosto (17 & 18). Specifically 

 they delved into the chemical, physical and 

 electrical properties of the compensating oil 

 used in the STAR series of submersibles (Pri- 

 mol 207, a hydrocarbon oil produced by 

 Exxon Oil) and its compatibility with nonme- 

 tallic battery components. They also looked 

 into the entire spectrum of bubble genesis 

 during charge and discharge of Exide MSC- 

 11 batteries. The results of this study are 

 summarized by the authors as follows: 

 "T/ie volume of gas produced by the 

 subject buttery during discharge at 

 elevated pressures is not directly de- 

 pendent on the magnitude of the ap- 

 plied pressure. 



The gassing behavior of the MSC-11 

 cell during discharge under pressure 

 is much more erratic than at atmos- 

 pheric pressure. 



A decrease in the gas producing abil- 

 ity of the battery along with a build-up 

 of battery by-products occurs more 

 quickly at pressure than under am- 

 bient conditions. 



Gas volumes entrapped by the battery 

 after dischxirge at pressure generally 

 vary from 100-155 ml. On occasion. 



Fig 7 1 1 Two pressure compensated systems STAR III (lelt) ot 60 cells and BELL FRANKUN (righl) of 378 cells (Gen Dyn. Corp. and NAVOCEANO) 



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