HUMPHREY INTERNAL-COMBUSTION PUMP 275 



It will be evident that in the next cycle, when admission of 

 combustible charge occurs, the surplus last rejected into reser- 

 voir x will want to enter first, because it is under slight pressure, 

 whereas inlet valve i has to be sucked open against its spring. 

 Consequently x will empty to atmospheric pressure each time 

 and only the additional mixture required will be taken in 

 through valve i. A slight modification may be made by trans- 

 ferring valve i from the pump to the reservoir x. 



The flexibility of the air compressor can now be studied. 

 To begin with the pump side, the level of the inlet valve e and 

 the rejected charge valve r are assumed to be variable, although 

 fig. 7, being merely a diagram, does not show how the pipes 

 carrying these valves are moved vertically. As the level of 

 these two valves controls the amount of charge ignited at each 

 cycle and the amount of the cushion space, their regulation is 

 all that is required to increase or diminish the energy developed 

 per working stroke. On the compressor side, the position of 

 the valves g and 5 controls the cycle of operations on this side 

 of the apparatus and renders it possible to compress either a large 

 volume of air to a low pressure or a smaller volume of air to 

 a high pressure or to make any intermediate changes which 

 may be desired. 



Thus all the conditions of output, up to the full limit of the 

 compressor, may be governed at will ; and for all ranges the 

 compression pressure of the new charge may be kept up to 

 the required degree, so that the apparatus works at its maximum 

 efficiency throughout the whole range. The amount of water 

 which oscillates between the chambers should theoretically be 

 altered along with the total capacity per working cycle ; but the 

 reason for this is merely to prevent the last portion of each 

 down-stroke from being wasted by taking in surplus combus- 

 tible mixture into one chamber or surplus air into the other 

 chamber to an undue extent. If the surplus of the combustible 

 mixture is unnecessarily large, the extra amount rejected will 

 increase the pressure in the reservoir x and this increase of 

 pressure may be made to govern automatically a water supply 

 and so bring up the total volume of reciprocating water or to 

 allow part of the water already in the apparatus to escape, so 

 as just to keep a small amount of excess charge for each cycle 

 no matter what may be the output of the pump. 



Turning now to the question of thermal efficiency, the curves 



