=========+======================+=========+==================
Size of | Pipe Size of Flanges | Size of | Capacity per Hour
Pump | Discharge | Suction | Pulley | Cubic Yards Sand
---------+------------+---------+---------+------------------
4 | 4 | 5 | 12 × 10 | 30 to 40
5 | 5 | 6 | 12 × 10 | 40 to 60
6 | 6 | 8 | 18 × 12 | 60 to 80
8 | 8 | 10 | 24 × 12 | 80 to 125
10 | 10 | 12 | 30 × 12 | 150 to 250
12 | 12 | 14 | 36 × 14 | 250 to 400
---------+------------+---------+---------+------------------
[Illustration: FIG. 497.]
Smaller sizes for pumping sand and gravel are made with cast chilled
linings with chilled piston, and brass covered shaft especially adapted
for stone and marble mills to carry the sand to the saws, or for mining
where there is a large quantity of sand to be pumped with water.
The table will convey an idea of the capacity, sizes, etc.
For pumping sand or heavy material the speed of pump should be
increased 25% more than for water.
[Illustration: FIG. 498.]
The engraving Fig. 497 exhibits a _steam-driven centrifugal pump_ of an
approved design constructed by the _Morris Machine Works_.
This pump is directly connected to the engine and has a double
suction. Pumps directly connected to engines are to be preferred over
belt-driven pumps when conditions of elevation, etc., will allow, as
they are self-contained, take up less space and are more economical.
The figure 498 shows a 20-inch _hydraulic dredge_, directly connected
to a 450 horse-power triple-expansion engine. A hydraulic dredge
consists mainly of a centrifugal pump with its driving engine and
boiler, and hoisting machinery for handling suction pipe and boat; the
pump in operation creates a strong suction flow in the suction pipe,
sufficient to pick up the material and draw it into the pump, from
which it is again delivered through the discharge pipe any distance
to point of delivery, and can at same time be elevated to reasonable
heights. Sand, mud, silt, etc., are readily picked up by the suction
force only, but where material is packed it must first be agitated.