A self priming pump is a unique kind of centrifugal pump that doesn’t require any external priming device. If a centrifugal pump is placed above a suction vessel or a sump, it develops what is known as a suction lift. This means that it has to be primed to eliminate any air from the suction casing and line and fill the suction casing with fluid before it can be started. Without performing this operation before starting the pump, the pump will simply not work, and the trapped air can cause damage to the pump’s bearings.
In a regular centrifugal pump operating with a suction lift, the priming operation is performed by pulling a vacuum pump or a plant vacuum system that is usually located at the top of the pump’s casing. A self priming pump eliminates the need for any form of external priming.
How a Self Priming Pump Works
When a self priming pump is shut down, the fluid drains out of the casing and suction line and flows back in the sump. However because of the self priming pump casing’s special design, a certain amount of fluid is retained at the bottom of the suction line. When the pump is started again, it goes through a self priming cycle that typically runs for several minutes. In the course of the priming process, the fluid that was retained in the pump’s casing is pumped out the discharge by the impeller, along with any air that went into the casing. The process creates a vacuum at the impeller’s inlet, which draws up fluid into the suction line. The priming process keeps going until all the air in the casing is forced out of the discharge and the fluid has moved up the suction line and into the impeller. When the pump is fully primed, it begins working like a normal centrifugal pump.
Applications of a Self Priming Pump
A self priming pump comes in a variety of designs and that are meant for various applications. A self priming pump can be used in any application that involves the use of a pump that is running with a suction lift. The pumps are however often more expensive that regular centrifugal pumps.
The most desirable feature of a self priming pump is the fact that it eliminates the need for any external priming procedures and eliminates the need for having any motors or bearings down in the pump’s sump. Normally, the suction lifts are restricted to approximately 20 feet with any self priming pump.
