Fig. 468. (See page [199].)
ROTARY PUMPS.
This class of pumps differs from the centrifugal pump, which is described and illustrated hereafter, in that it includes a revolving piston, while in the centrifugal pump there is a set of revolving blades which acts upon the liquid in the same way as a fan acts upon the air; the centrifugal pump receives the water in the center and throws it outward, while the rotary gathers the fluid up and leads it towards a central discharge.
The rotary pump substantially corresponds to the pressure blower, and in many cases is simply the rotary engine reversed; while the centrifugal pump is analogous to the fan-blower. The functions of a rotary are almost identical with those of piston and power plunger pumps.
The rotary pump on account of its cleanliness has been quite generally adopted for pumping all heavy liquids, such as starch, paint, soap, gummy oils, beer and hops, sewerage, bleachers, etc.
The rotary pump is used also in places where a piston or steam pump would be objectionable either on account of floor space occupied or for the reason that steam could not be had without too much expense for lifting and forcing water and other liquids which would not nor could not find their way through the tortuous and narrow passages of the average piston and plunger pumps.
For low heads of liquids the rotary is also somewhat more efficient than direct acting pumps and the absence of close fitting parts renders it possible to handle water containing a considerable quantity of impurities, such as silt, grain and gravel. This type of pump is compact and is generally self-contained, especially in the smaller sizes, and will deliver more water for a given weight and space occupied than the reciprocating types, while its simplicity of construction not only lessens the liability to derangement, but enables persons having a limited knowledge of machinery to set up and operate these pumps successfully.
Rotary pumps are driven by means of belts from line shafting and by wheel gearing, and also by direct connection to any prime mover such as a steam or gas engine, hydraulic or electric motor.