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Why is priming necessary in centrifugal pumps?

Why is priming necessary in centrifugal pumps?

Centrifugal pumps are used to move liquids by using rotational motors called impellers. Fluid enters the impeller along its axis and is pushed out due to centrifugal force along the circumference. Impellers are required to increase the velocity and pressure of the fluid to guide it to the pump’s exit. 

Priming a pump refers to removing air from the pump and suction line. It is the most important thing to do before actually operating a pump. Neglecting priming can cause issues in pump maintenance and impact the downtime of the piping system.

These are the two main benefits for priming in centrifugal pumps:

  1. Priming is vital to reduce the chances of pump damage in the start-up phase. It prevents the pump impeller from becoming air-bound. If air fills in the pump it will not be able to pump desired liquid.
  2. Priming eliminates the risk of the pump overheating and can even cause damage to critical internal pump components.

 

Here is how the process of priming takes place:

  1. The suction pipe and impeller are filled with water.
  2. The pump is started after the delivery valve is closed.
  3. The rotating impeller forces the water to the delivery pipe, opens the delivery valve and the water is sucked through the suction pipe. 

 

A pump can be primed in different ways. They are as follows:

  • Manual priming

To manually prime a pump liquid is poured into it. This can be done using a funnel or directly pouring into the suction pipe. The pump will be primed with the help of a gravity feed. 

 

  • By using a vacuum pump

A small vacuum pump is used here to prime the main centrifugal pump. The suction line of the vacuum pump is connected to the discharge line of the centrifugal pump. The small pump removes all the air from the primary pump and suction piping.

 

  • Using a jet pump

Water from a high head is made to flow through a nozzle in this method. The pressure outside the nozzle is less than atmospheric pressure. So it is possible to suck water from the sump.

 

  • Installing a foot valve

In this method a foot valve is installed in the suction piping to make sure that liquid doesn’t drain from the casing of the pump once the pump stops operating. Once the pump stops and the foot valve’s port closes, the liquid can’t drain back into the suction pump because the valve is tightly sealed.  

 

There are some situations where priming a pump isn’t required.

Let us look at what those are:

  • When the pump is submerged
  • If the pump is at a lower elevation compared to the supply so that the pump suction will be filled with liquid all the time
  • In case of self priming pumps

 

With some basic modifications, centrifugal pumps can be made self-priming. This means that the liquid stored in the pump has the ability to generate a vacuum on the suction line. Even a self-priming centrifugal pump cannot operate when dry. 


 

To get the most out of your investment while buying centrifugal pumps, make sure to get it primed at the right time. If you purchase from a reliable and well-established dealer, they will guide you on this process. 

 

Udyog Engineering is one such company that not only provides top-notch equipment but is your advisor on selecting and maintaining your machinery to the best possible way.

 

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