virtue of a mechanism which senses varia- 

 tions in cabin atmospheric pressure. 



In a few vehicles the first approach is 

 taken and, although not recommended by 

 ABS or MTS, has worked satisfactorily with 

 no reported accidents. The procedure is quite 

 simple: A timer (quite frequently a kitchen 

 alarm clock) is set to ring every half hour or 

 so; when it does, the operator resets it, takes 

 a reading of oxygen or cabin pressure and 

 then, if necessary, opens the tank to admit a 

 certain amount of oxygen. 



In the second approach, the supply of oxy- 

 gen is fed through a flow control valve, 

 thence through a flow indicator and finally 

 into the cabin. In this procedure the oxygen 

 is continually bled into the cabin at a rate 

 somewhere near 0.85 SCFH for each person. 



The system still requires periodic monitoring 

 to assure steady flow as internal tank pres- 

 sure decreases or as cabin temperature var- 

 ies. The system shown in Figure 9.2 is DS- 

 4000''s, and it includes a pressure regulator 

 which maintains a downstream pressure of 

 80 psi (±10 psi) from a 3,000 psi tank as long 

 as the storage pressure exceeds 80 psi. A 

 further feature of this system is the air 

 mixing duct, which mixes oxygen with cabin 

 air and then blows the mixed air downward 

 and across the viewport (Fig. 9.3). Whereas 

 the steel pressure hull cools in accordance 

 with ambient water temperature, fogging 

 and drippage of condensed water on the 

 viewport is common. With the modification 

 shown, the forced air keeps the viewport dry. 

 Eliot (4) cautions that the air flow should be 



Fig. 9.3 Ducts above DEEPSTAR 2000 s viewports blov» cabin air mixed v»ith oxygen across the viewports to remove condensed moisture and prevent togging The small viewport 



between the larger two is tor photography. 



415 



