LAND DRAINAGE BY MEANS OF PUMPS. 39 
quantity pumped must decrease. Along the upper Mississippi and 
the Illinois River the greatest demand on the pumping plant usually 
occurs at the time when the head pumped against is greatest. If the 
speed of the pump be fixed to give full capacity at the greatest head, 
at lower heads the discharge of the pump will be greatly increased 
and the efficiency much lowered. As the average lift will be much 
lower than the maximum, usually scarcely half, the yearly efficiency 
of the pump will be small and the consumption of power large. By 
far the better method is to connect the pump and the motor by 
means of a belt with three sizes of pulleys or with silent chain drive 
with two or three sizes of sprocket wheels. The pump speed can 
then be altered to suit the head. In Louisiana, where the fixed- 
speed ratio is used, the greatest demand on the pumping plant occurs 
at the lowest head, and as the head increases the amount of water to 
be pumped greatly decreases; consequently the capacity of the pump 
fits the need. 
AUXILIARIES. 
The steam plant will require the usual auxiliaries. A surface 
condenser will furnish pure feed water, but some form of jet con- 
denser is simpler and cheaper. For priming the pumps a steam 
ejector is the simplest arrangement, though an air pump may be 
used. Separators and traps, filters and heaters, should be used as 
needed for safe and economical operation. Piping and boilers 
should be well covered, to reduce as much as possible the amount of 
radiation and condensation of steam. 
In large plants boilers, engines, and pumps should all be divided 
into two or more equal-sized units, so arranged that they can, when 
necessary, be operated independently, and the auxiliaries should be 
installed in duplicate. 
CALCULATION OP THE SIZE OE PUMPING PLANT. 
To illustrate the method of determining the size of machinery to 
be installed in a pumping plant, the calculation will be made for a 
district of 10,000 acres. To remove a depth of water of one-fourth 
inch over the whole district in 24 hours will require a capacity of 
105 cubic feet per second. For such a district it will be best to use 
two separate pumps, which should be identical in size. A 30-inch 
pump will be rated at about 49 cubic feet per second, a 32-inch 
pump at about 56 cubic feet per second, and a 36-inch pump at 
about 71 cubic feet per second. In this case it would be best to use 
two 32-inch pumps, which would seem to have a slight margin of 
excess capacity. However, since pumps of this style so frequently 
fail to have the capacity assumed, they should be taken only under 
the guaranty of the manufacturer and subjected to a thorough test 
after they are installed. The pumps will need to be run at about 
