52 BULLETIN 300, U. S. DEPARTMENT OF AGRICULTURE. 
silt or fine sand are easily carried in suspension, and for these a 
larger diameter of discharge pipe with a lower velocity may be used 
than for coarse sand and gravel. The maximum velocity of dis- 
charge is reached when the friction head begins to increase too 
rapidly. The velocity at which the abrasive action on the internal 
surface of the discharge pipe begins to be serious occurs at about 
12 feet per second for pipes 20 inches in diameter. The gain in the 
proportion of solids transported at high velocity may be offset by 
the cost of more frequent renewals of discharge pipe. Discharge 
pipes having a diameter of 15 inches and a thickness of wall of 
eleven-sixty-fourths inch, and containing from 0.5 to 0.6 per cent of 
carbon and from ().6 to 0.7 per cent of manganese, have passed more 
than 300,000 cubic yards without wearing out. Since the wear is 
chiefly along its bottom, the pipe may be marked and rotated a 
quarter turn occasionally to insure even wear. 
The smaller the diameter of the discharge pipe the higher the 
velocity for a given discharge, and the greater the percentage of 
solids which will be transported. The larger the discharge pipe 
the greater the volume of mixture carried for a given amount of 
power. ‘The amount of power must be determined that will give 
sufficient velocity to carry the material in suspension and deliver the 
maximum amount of solids. With 6-inch pipe or less, sand mix- 
tures will flow well with a pipe velocity of 5 feet per second. In 
a 20-inch pipe it has been found that a velocity of 10 feet per second 
will transport sand. 
The smaller pumps, 12 inches and under, may be his belt-driven 
or direct-connected to the power unit. T ne larger pumps are usually 
direct-connected to the power unit, this srEdnae of drive being the 
most economical. When there happens to be great variation in the 
length of discharge pipe it is advisable to have impellers of differ- 
ent diameters—one of large diameter when long discharge pipes 
are used and a smaller impeller with a short discharge pipe. By 
using the proper size of impeller the engine is better able to main- 
tain its normal speed. 
DETERMINATION OF SIZE OF PLANT. 
‘To determine the amount of power required to operate the pump 
the following factors must be considered: (1) diameter of suction 
and discharge pipe; (2) kinds of pipe and length of each kind; (3) 
character of end connections; (4) static head; (5) efficiency of pump 
and engine (which may vary from 30 to 70 per cent) ; and (6) nature 
of material and percentage of solids transported. 
