After the pump has been properly primed, it should be started before the gate valve on the discharge is opened. When full speed is reached, the discharge gate may be slowly opened, and the pump will perform its work.
Note.—The Worthington centrifugal pumps are divided into three classes, viz.: Conoidal, Volute and Turbine.
The Conoidal Centrifugals (named from the cone-shaped impeller) are designed especially for low lifts and large deliveries and are adapted to irrigation work, the handling of sewage and similar purposes. They are comparatively inexpensive and operate at high rotative speeds, making possible direct connection to electric motors. For heads up to 30 feet they are unexcelled in the pumping field.
The Volute Centrifugals (illustrated on page 232) are built for medium lifts, but for all capacities. Since they run at moderate speeds, diffusion vanes are not needed, but the volute casing has been carefully designed to obtain high efficiency and 86% has been shown under test. These pumps are recommended for heads up to 70 feet, although they will safely withstand 150 feet.
It is always best to use a foot valve in connection with centrifugal pumps where the lift is more than three to four feet, and even under these low lifts where long suction pipes are used to conduct water long distances, foot valves should always be used to keep the pump and suction pipe charged.
Figs. 1, 2 and 3.