PUMPING MACHINERY OF THE WATER AND SEWERAGE BOAKD. LV. 



as a balance piston, except that it was not a piston but a 

 balancing ring. Many of the vertical centrifugal pumps 

 with which I had to do years ago, had the thrust also taken 

 up by collars on the shaft, which proved for moderate 

 pressure a very satisfactory method. Some makers used 

 what was termed an onion bearing, which gave greater 

 flexibility, but which required to be made very large to 

 afford the surface necessary. With pumping machinery 

 where the head is known and with steady steam pressure, 

 it does not appear to be an advantage to provide automatic 

 expansion and the refinements necessary, as the work 

 done is generally a steady one, such variations as occur 

 in it being at definite times and always known before- 

 hand, so that expansion valves which can be varied by 

 hand will answer as satisfactorily as the more expensive 

 automatic gear. The engine to which Mr. Furniss refers 

 at Spottiswoode as being so very economical, is fitted with 

 a very elaborate automatic expansion gear which can only 

 add to the friction and the cost. The work it has to do 

 being practically constant, the only variation in the 

 pressure in the delivery main is due to the number of 

 engines working into it and their speed. 



In low lift pumping machinery, the percentage of indicated 

 horse power in the steam cylinders, utilised as pump horse 

 power, is invariably low, so that it is not fair altogether to 

 criticise the steam end of all pumping engines by the steam 

 consumption per pump horse power per hour, for with the 

 same steam end connected to a pump working against the 

 greater pressure, it will be found that the efficiency is 

 much higher for the friction of plungers and glands, and 

 the resistance of the pump valves is nearly constant, being 

 independent of the pressure, and of course at low heads 

 form a greater proportion of the total head than at higher 

 pressures. 



