Understanding Centrifugal Pump Priming

Centrifugal pumps are widely used for moving liquids. However, they are not self-priming in most cases. This means that before a centrifugal pump can start pumping liquid effectively, the pump casing and the suction pipe must be filled with the liquid to be pumped. Any air or gas present in the casing needs to be removed.

What is the Process of Priming?

The process of removing air, vapours, or gases from the casing and suction pipe of a centrifugal pump and filling it completely with the liquid being pumped is known as priming. Priming is essential because centrifugal pumps rely on the centrifugal force exerted on the liquid by the impeller to create pressure and move the fluid. If the casing is full of air, the impeller will just spin in the air, and no significant pressure will be developed, hence no liquid will be pumped.

Methods of priming include:

• Filling the pump casing and suction line manually through a priming port.
• Using a vacuum pump or ejector to remove air from the casing.
• Using a foot valve at the end of the suction pipe to keep the pipe full of liquid when the pump is stopped.
• Installing the pump below the level of the liquid source (suction lift) so that the liquid flows into the pump by gravity.

Analyzing the Options

Let's look at the given options:

• priming: As discussed, this is the specific process of filling the pump casing and suction line with liquid and removing air to enable the centrifugal pump to operate.
• sweeping: This term generally refers to cleaning or moving something across a surface, not a specific process in pump operation.
• pumping: This is the general action of moving fluid using a pump after it has been primed. It is the outcome, not the process of preparing the pump to move liquid by removing air.
• surging: This refers to an unstable flow condition that can occur in pumps or compressors, often characterized by oscillations in flow and pressure. It is unrelated to the removal of air before starting operation.

Based on the definition, the process of removing air inside a centrifugal pump and filling it with liquid to be pumped is correctly identified as priming.