is once more the *bathycire' wax. Below k the copper wires are bent in 

 a zigzag to prevent them from being pulled through the Araldite. 



Appendix lo 



The Reciprocating Valves 



The hull must be able to 'breathe' if the volume of the petrol 

 changes as a result of variations of pressure and temperature. We 

 have seen (page 77) why we only allow water (which ought to be in 

 the lower part of the float) to enter and leave the central compartment, 

 compartment No. 7 (Fig. 8, page 76). 



This being so, we could have been satisfied with a simple opening L 

 placed at the bottom of this compartment. I added above this opening 



Fig. 25. Reciprocating valve 



the piping and the double valve F (represented diagrammatically in 

 Fig. 8) to avoid, if possible, and anyway to lessen the consequences of, 

 a leak in the upper part of any of our compartments. Let us imagine 

 a small accidental opening in the top of the float in compartment No. 

 9, for example. If the float were simply open at the bottom towards L, 

 the petrol pushed by the pressure of the water would gush out in 

 floods and, what is worse, the petrol in the central compartment. No. 

 7, might follow it as a result of siphoning action. A glance at our 

 sketch will make the role of the double valve clear. Normally, if 

 there is no leak anywhere, the hull will breathe by this valve. When (at 

 the moment of a dive or at the moment of a lowering of temperature) 

 the water must enter the float, it will enter by L, will raise the lower 

 flap-valve and will reach the base of the float. This flap- valve, however, 

 is loaded in such a manner that it will only open if the pressure exceeds 



[ 176] 



