LAND DRAINAGE BY MEANS OF PUMPS. 35 
as are under discussion it probably does not depend much upon the 
length of time the plants are in operation each year. What amount 
to allow for depreciation is a difficult matter to decide The length 
of time before such machinery will wear out depends chiefly upon 
the original quality of the installation and the care that is taken of 
it afterwards. We can not safely assume that such machinery will 
last more than 20 or 25 years. Much of it will be discarded sooner, 
either because it is outgrown or worn out. With proper care it is 
probable that such machinery may be made to endure twice as long 
as it will last if it is carelessly treated. It is customary to include 
with depreciation an item for repairs. This should be very small 
during the first few years of the life of a well-constructed plant, but 
will grow larger as the plant becomes older. 
The cost of fuel per year depends to a considerable extent upon the 
kind of machinery used and also upon the amount of time the plant 
is run. Whenever a steam plant starts there is a certain consumption 
of fuel in preparation before starting, the heat value of which is lost 
when the plant is stopped. Hence, since the operation of a pumping 
plant is very intermittent, the fuel consumption is not strictly pro- 
portionate to the time run. The amount of fuel used also depends 
largely upon the skill of the fireman. An unskillful man may easily 
use 25 per cent more fuel than is really necessary. Different types of 
equipment require different amounts of fuel to produce the same result; 
that is, some types are more economical of fuel than others. The 
cost of the labor at the pumping plant depends upon the class em- 
ployed and the length of time it is required. The cost of electricity 
per year depends on the type of pump and the care used in installa- 
tion, as well as upon the total time the plant is run. The distance 
from the transmission lines of the large power companies will influ- 
ence the power rate. On the larger districts the power rate is usually 
less than on the smaller ones. 
In general, in a given location, that type of pumping plant will be 
best which requires- the least annual cost, including all the elements 
enumerated above. To a certain extent, variations in these different 
elements tend to offset each other. For example, a highly efficient 
plant from the point of view of fuel economy is complicated and 
expensive, and hence will have a relatively high charge for interest 
and depreciation. Likewise, it will require skillful and high-priced 
attendance, but may, on the other hand, in a large plant, require 
fewer men. If cheap labor is employed, the coal and repair bills 
will be increased and the deterioration of the plant will be more rapid. 
The advantage of fuel economy is relatively more important in loca- 
tions where fuel is especially high, and in a large plant than in a small 
one, but in any plant it diminishes in importance as the time of run- 
ning per year decreases or becomes much interrupted. 
