EXCAVATING MACHINERY USED IN LAND DRAINAGE 55 
If the pipe lines make four elbow turns and the friction loss in the 
suction pipe, which is seldom more than 25 to 40 feet long, is omitted, 
the total head to be pumped against is as follows: 
Feet. 
Static head (difference in elevation of water surface and top of levee) __~____ 20 
Friction loss in 2,000 feet of 14-inch discharge pipe_______ Rat se yen cia sae 63 
Possiarnede m4, elbow burns no ee a yc a tS Ne eae 8 
LDUPINPE TGS LGR nn eA a Sa i ce en ole i! Sa ahd Se U6 poll 2 
Loamishead=torbespuimpedsagainsts = 2 eT te She a ee 93 
Table 22 shows that approximately 3 horsepower is required for 
each foot of head to make a 12-inch centrifugal pump deliver 130 
cubic yards of solids per hour in a 10 per cent mixture. It would, 
therefore, be necessary to have 279 horsepower available to pump 
against the required head of 93 feet. As it is advisable to have ample 
power available, a 300 or preferably a 350 horsepower engine should 
be used. If electric power is used, a 400-horsepower motor should be 
installed, as electric equipment can not successfully be subjected to 
overload as can steam equipment. 
In determining the size of plant required it is important to provide 
ample reserve power and capacity. This is necessary because of the 
many variable and unknown factors entering into the operation of 
hydraulic dredges. A choked suction pipe, pump, or discharge pipe 
can frequently be corrected without serious loss of time if ample 
reserve power is available. 
OUTPUT. 
The amount of material pumped in a unit of time and the fuel 
consumption per cubic yard pumped vary, of course, with the kind 
of material pumped and the conditions under which operations are 
conducted. The information given in Table 24 is representative of 
this type of dredge. : 
In the operation of hydraulic dredges there is considerable lost 
time, due to delays caused by such items as changes in discharge pipe, 
choked suction pipe, pump, or discharge pipe, repairs, and renewals. 
Not more than 50 to 75 per cent of the time will be spent in actual 
operation. 
