42 BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 
provide for the maximum demand. The question of adjustment of 
speed has already been discussed. 
If it were desired to provide for a greater depth of water removed 
per 24 hours, the proper additions could be made to the above results. 
The boiler capacity required would depend upon the particular 
engines used, upon the number and kind of auxiliaries, and upon 
the quality of coal to be used. For a plant of this kind, however, 
the nominal boiler horsepower should be at least as large as the rated 
engine horsepower. The boilers must have a capacity amply suffi- 
cient to supply safely all the steam needed by the engines when oper- 
ating at their maximum overload. This may be secured by addi- 
tional boilers or by forcing the boilers, when necessary, through 
appliances for producing an artificial draft. In general, large engines 
of the best types require less steam per horsepower than smaller ones. 
In a very large plant the nominal boiler horsepower may be less 
than the engine horsepower. 
In designing such a plant, all the elements must be carefully calcu- 
lated to secure in each the necessary maximum capacity. It is 
especially needful that the auxiliaries be large enough. A deficiency 
in some single comparatively slight but essential element may hinder 
the operation of the whole plant. Durability and reliability in 
workmanship and materials may be secured to some extent by 
specifying that the boiler shall be capable of operating at a higher 
pressure than its regular working pressure, and that the engines 
shall be able to run with higher steam pressures and at higher speeds 
than the normal. Descriptions of a large number of pumping 
plants and the results of tests are given in detail in a previous 
bulletin. 1 
BUILDINGS AND FOUNDATIONS. 
The machinery should be inclosed in a substantial and durable 
building. The foundation of the building, and especially of the 
machinery, should be prepared with great care. As the soil condi- 
tions are very likely to be bad, careful investigations should be 
made by means of borings. Nothing should be assumed. Failure 
to make such borings has many times resulted in great difficulties 
during construction, and in at least one case in failure after com- 
pletion. The results of such investigations will sometimes show 
that the proposed site of the plant must be changed. Drainage 
district officials who are responsible for the construction of the plant 
should not only make certain that the proposed foundation will 
prove satisfactory under the prevailing soil conditions, but should 
allow only those to do the work who are experienced in building 
foundations under such adverse conditions. Inexperienced con- 
i U. S. Dept. Agr., Office Expt. Stas. Bui. 1S3, Mechanical Tests of Pumps and Pumping Plants 
used for Irrigation in Louisiana in 1905 and 1906. 
