Village Sauitarij Eco}iOinij. 
233 
applied is the centrifugal pump,* wliicli svas invented not 
many yeais ago, and first obtained j)rominent notice during the 
Exhibition of 1851. Since that period a large number of tliese 
pumps have been brought into use for drainage and other 
purposes, where large quantities of water have been dealt with. 
They recjuire considerable velocity, and when once at work any 
increase in speed greatly augments the quantity raised ; for 
instance, if the velocity of rotation be doubled, the quantity of 
water raised is quadrupled. The disadvantages of these pumps, 
when worked by wind engines, are, that there is more complica- 
tion of wheel work than in others, and there is a positive 
necessity for a certain minimum speed being attained before 
any water at all can be raised. This is not the case with the 
noria or ordinary pumps, which raise a quantity in proportion 
to their speed, however slow that speed may be. 
Although the ancient noria and the modern centrifugal pump 
may, in certain instances, be found very appropriate, neither one 
nor the other possesses the universal applicability of such pumps 
as are now commonly used and known under the two heads 
of lift pumps and force pumps, which are most frequently com- 
bined in such operations as those now under consideration. The 
lift pump owes its action to the pressure of the atmosphere alone, 
the movement of the bucket creating a partial vacuum, which is 
filled by water forced upwards by the })rcssure of the air on the 
surface of the water in the well. Although the maximum eleva- 
tion to which atmospheric pressure can raise a column of water 
is 33 feet, it is found practically that a vertical height of 25 feet, 
should not be exceeded. In all cases it is desirable to avoid 
suction, as far as possible, by placing the pumps near to the 
level of the water in the well, and using the power at command 
for forcing the water upwards rather than lifting it by suction. 
The force pump, in the correct application of the term, does 
not make use of atmospheric pressure at all, but the water flows 
into its barrel, and is forced up an ascending pipe by direct 
pressure. It is true that great objection is entertained to pumps 
of any description when applied to deep wells, but this is due in 
great part to inferior and disproportionate workmanship. For 
all moderate elevations the common plumber's pump may be 
appropriate enough, but for deep wells it has often been found to 
fail from the want of that strength and correct construction 
which are more frequently attained in what may be called the 
" engineer's pump." With a lift of 60 feet from the surface of 
* Messrs. Easton, Amos, and Anderson, of Southwark, are the makers of the 
centrifugal pump known as " Appold's ;" and Messrs. Gwynne and Co., of Essex- 
street, Strand, are the makers of the pump whieh is known hy their name, and 
wliich they recommend for wind-engii:es. 
