ENGINE No. 81. 



Compound duplex direct acting pumping engine. 



These diagrams show the effect of increasing the throw of 

 the valves (which are slide valves), thereby giving the engine 

 the benefit of wider opening of ports. The improvement is 

 shown mainly in the increased effect of the vacuum in the low- 

 pressure cylinder. The effect of the change on the duty per- 

 formed by the pump was marked, and the consumption of coal 

 was much reduced. No. 81a was taken before, and No. 

 after, the change. 



ENGINE No. Sla 



304 



