The difference between centrifugal pumps and self-priming pumps
Pumps are used for various purposes in many different fields. Depending on what you need to achieve, you can choose from various types with different features and specifications.
People very often wonder what is the difference between a centrifugal pump and a self-priming pump, as they think they both belong to the same category.
In actual fact, this is not really the case. Although self-priming pumps can be considered to be classic centrifugal pumps, they are primed in a different way.
But what does “priming” actually mean?
A pump is primed when the pump body and the intake pipe are full of the liquid for pumping, with no trace of air remaining. In this condition, the pump moves the liquid and reflects the performance stated on its specifications curve.
Let’s look at that in more detail.
Centrifugal pumps: use and fields of application
Let’s focus on non-self-priming centrifugal pumps first, some of the most common types of pumps.
As the name suggests, centrifugal pumps move the water by means of centrifugal force. The liquid enters the pump through its suction inlet and is made to “centrifuge” by one or two impellers and then driven towards the pump discharge.
In this case, the priming is done manually and you have to make sure the pump primes each time it is put into operation, so the intake pipe must always be full of liquid.
They are versatile and efficient, making them ideal for use in various fields, such as the chemical and petrochemical industry, the pharmaceuticals sector, or for water processing and purification.
As far as their practical application is concerned, classic centrifugal pumps can be used in two ways:
- under head, placed at a lower level than the liquid;
- over head, placed at a higher level than the suction liquid.
In the former case, the force of gravity alone drives the liquid into the pump; in the latter, the liquid has to be pushed “up the pipe”, or you have to make sure the liquid never drains out of it. A foot valve combined with a tank ready to fill the pipe can be enough to guarantee priming, but the pump may not be able to prime if the valve fails or if the suction liquid contains solid particles capable of blocking it or keeping it open.
This is where a self-priming pump comes into play.
Self-priming pumps: use and fields of application
Self-priming pumps are able to prime on their own, without the need for any manual procedure. There are several types of self-priming pumps. The most common types are those with a check valve built into the pump body, like the Robusta line.
To ensure self-priming, you have to fill up the body of the pump with water or a liquid that is compatible with the liquid for pumping. The impeller creates internal turbulence capable of removing the air from inside the intake pipe, producing a depression, and then subsequently expelling it through the delivery pipe. The water now rises up through the intake pipe until it fills completely, without the need for a foot valve.
As a result, the pump starts running.
Where can they be used? Readily and for different types of liquid, for domestic, agricultural, construction and industrial applications.