HUMPHREY INTERNAL-COMBUSTION PUMP 265 



thus again involving four strokes of unequal length. In this 

 case the water column has only one outward and one inward 

 movement per cycle but the expression " two-stroke " would 

 here be misleading, unless one remembers that it applies only 

 to the water column and does not refer to what occurs in 

 the combustion chambers. 



Let us follow through the cycle in this case, assuming that 

 a compressed combustible charge exists in the top of chamber 

 a and that b is full of water. Explosion and expansion in a 

 cause the outward propulsion of the water column and when 

 atmospheric pressure is reached the exhaust valve of a opens, 

 water flows in to follow the column and to rise in a expelling 

 burnt products ; as there is insufficient pressure to maintain the 

 water in b, the level therein then falls, causing an intake into b 



AflmlBs'on 

 Eihaust (-v| V" " S ,H Exhaust 



Fig. 2. 



of a fresh combustible charge. All this takes place during the 

 outward movement of the column of water. Then the column 

 which is coming to rest commences to return towards the 

 chambers ; it finds that the remaining burnt products in a can be 

 readily sent out through the still open exhaust valve, whereas the 

 new charge in b cannot escape, as the admission valve which 

 admitted the charge is now shut under the action of its spring; 

 consequently the column rises at first in a until the exhaust 

 valve is shut and then in b, compressing the new charge. 

 Ignition in b starts a fresh cycle with the functions of a and b 

 reversed. 



There are important differences to be noted between the 

 action of this pump and of the single- barrel pump first 

 described. To begin with, the new charge is taken in merely 

 by water falling under the action of gravity and does not 



