LXX. T. H. HOUGHTON. 
This is better than those plotted on the diagram, but the height 
of lift is beyond the limit to which it was intended to refer in 
this paper. 
Probably more centrifugal pumps are used for low lifts than 
any others, and when properly designed for the work they have 
to do, none are more efficient when raising water to heights not 
exceeding 30’ to 40’, beyond that height the efficiency falls off. 
In Figure 1 are shewn the results of a number of tests of these 
pumps by good makers, and it will be noted, that they give for 
lifts up to 30’ better results than reciprocating pumps, each 
pump however, only does its best at a certain lift and delivery 
any variation in either quantity or lift reducing the economy. 
The best results that have been obtained with centrifugal pumps 
are in Egypt, with some large pumps made by Messrs. Fariot of 
Paris, which gave an efficiency of 657%, and some pumps made by 
Gwyne for the drainage of Haarlem Meer, which on 15’ lift shewed 
an efficiency of 65-77. 
Since the centrifugal pump was introduced by Mr. Appold at 
the 1851 Exhibition, many experiments have been made to deter- 
mine the most suitable form of casing, and shape of the vanes, 
and at the present time the best results are generally obtained 
with the spiral casing and curved vanes, pumps with radial vanes 
giving a much lower efficiency. Figure 6, shews a section 
through a pump with spiral casing, and curved vanes. In order 
that the water may pass through the fan of the pump without 
shock, it is necessary that the angle of the vanes with the inner 
and outer circumference, should be the resultant of two forces, 
namely, one the direction and velocity of the radial flow of the 
water entering or leaving the wheel, and the other the tangential 
velocity of the circumference, this is shewn in Figure 6, where 
v' and v* are the radial velocities of the water entering and 
leaving the wheel respectively, and s' and s* the tangential speed 
of a circumference, completing the two parallelograms, the 
etn 
1 Engineering, Jan. 28, 1887. 
