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SCIENCE PROGRESS 



4. Second return of water column towards a, giving com- 

 pression stroke. 



It is obvious that a partial vacuum corresponding with the 

 height of the suction lift must be produced in the chamber a 

 in order that the fresh liquid may be drawn in past the 

 valve g; this necessitates the size of the combustion chamber 

 a being made large enough to admit the necessary expansion 

 down to the partial vacuum required. For large suction lifts 

 this would prove a disadvantage and it is better in such 



Fig. 5. 



cases to make the vacuum which draws in fresh liquid in- 

 dependent of the degree of expansion of the combustion 

 gases. Such an arrangement is shown diagrammatically in 

 fig. 5, where 1 is the combustion chamber and p is a piston 

 sliding easily in the chamber the motion of which can be 

 arrested by the elastic buffer-stop s, here shown as a number 

 of rubber ring but which can be an air-cushion or any suit- 

 able form of dash-pot. Pipe q conveys the low level liquid 

 to the closed suction tank s t which surrounds the water 

 valves w and has an air cushion on top. As the piston p 



