Exam Question
(a) Describe why priming is required for a centrifugal pump. With the aid of a sketch, describe working of a primer for centrifugal pump. (10)
(b) Why balance holes are provided in the impeller? (6)
Class 4 (4th Engineer)
MEP
📅 Jan 2026
Reference Answer
### (a) Priming of a Centrifugal Pump and Primer Operation
**(1) Reason for Priming**
Priming is the process of filling the pump casing and suction line with the liquid to be pumped, ensuring that all air is expelled before the pump is started. For a centrifugal pump, this is a mandatory pre-condition for operation. The reasons are based on fundamental fluid dynamics principles:
* **Operating Principle**: A centrifugal pump operates by imparting kinetic energy to a fluid via a rotating impeller. This energy is then converted into pressure energy in the volute casing. The pressure head (H) generated is directly proportional to the density (ρ) of the fluid being pumped, as given by the formula $$ H \propto \frac{u^2}{2g} $$, and the resulting pressure is $$ P = \rho \times g \times H $$.
**(1) Reason for Priming**
Priming is the process of filling the pump casing and suction line with the liquid to be pumped, ensuring that all air is expelled before the pump is started. For a centrifugal pump, this is a mandatory pre-condition for operation. The reasons are based on fundamental fluid dynamics principles:
* **Operating Principle**: A centrifugal pump operates by imparting kinetic energy to a fluid via a rotating impeller. This energy is then converted into pressure energy in the volute casing. The pressure head (H) generated is directly proportional to the density (ρ) of the fluid being pumped, as given by the formula $$ H \propto \frac{u^2}{2g} $$, and the resulting pressure is $$ P = \rho \times g \times H $$.
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