What is Self Priming Pump? | How does Self Priming Pump work?

The self-priming pump is a most common type of pump. This type of pump has a unique design. As the name suggests, it can prime itself under suction lifting condition. This article mainly explains the types, working, and advantages of the self-priming pump.

What is a Self-Priming Pump?

A pump that has a self-priming capacity is known as a self-priming pump. The self-priming pump is also known as a suction pump.

This pump installs fully or partly above the liquid level so that air can easily enter the suction pipe. You need to displace or evacuate the suction pipe before the pump can deliver fluid.

You can use different methods to evacuate the suction pipe. You may also use a secondary pump to evacuate the suction pipe. A check valve may also be employed to prevent liquid from draining out of the suction pipe when the pump is shut off. However, all of these solutions need additional devices, piping, and processes.

What are the Problems with Self-Priming Pumps?

Multiple factors may affect the self-priming capability of the pump. Following are some important tips to prevent your pump from problems:

  1. The drain pipeline of your pump shouldn’t be clogged or pressurized.  
  2. For all types of pumps (i.e., centrifugal pump and positive displacement pump), the suction pipeline should be airtight.
  3. The air flow into the pump must be continuous, the pressure shouldn’t drop, and liquid shouldn’t enter the suction pipeline.
  4. The suction side pipeline should have a minimum area to decrease the priming time. If the prime time is too long, the charge may evaporate before the priming process. Due to evaporation of the liquid charge, the pump will start dry running, which may cause pump failure.  

In a centrifugal pump, the factors affecting the efficiency of the impeller limit the pump priming capability.

  1. If the pumping liquid has trash or solid, it can accumulate in the return port and prevent the liquid from circulating and generating a liquid ring. The accumulation of solids in the impeller area decreases the eye’s capability to create low-pressure areas.
  2. As the wear and tear issues or age of the pump increases, the clearance between the volute casing and the impeller also increases, stopping the pump from creating low-pressure areas.
  3. The incorrect assembly of the pump parts may also affect the internal clearance.
  4. If the pump is used in cold environments, it is important to drain or warm the pump if the temperature drops below freezing. Freezing water in pumps or pipes can cause damage.

Are Positive Displacement Pumps Self-Priming?

All types of positive displacement pumps have good self-priming capacity. These types of PD pumps are diaphragm pumps, vane pumps, piston pumps, plunger pumps, lobe pumps, and gear pumps.

The positive displacement pump contains tight tolerance components to prevent liquid from flowing backward from the outlet to the inlet side. According to the usefulness of these seals produced by the tight tolerance components, positive displacement pumps have the capacity to discharge air from their suction pipeline to some degree. However, running dry can cause the pump to overheat, which can lead to seal wear and pump failure.

The reciprocating pump has a risk of cavitation on the stop when liquid enters the pump, and a liquid-air mixture is already present in the pump. Under such a situation, air bubbles generate and expand on the inlet side. When it reaches the high-pressure outlet side of the pump, the bubbles collapse violently, producing vibration and fail to the pump parts.

For these reasons, it is important to consult the manufacturer before using positive displacement pumps in applications that must be self-priming and idle for long periods of time.

Advantages of Self-priming Pump

  • These pumps have self-priming capacity.
  • These pumps can handle different types of fluids.
  • These have the capability to pump suspended solids, corrosive liquids, and slurries.
  • Compared to a submersible pump, the suction pump continues to transfer liquid when the pump is no more immersed in a liquid container or tank.
  • Best appropriate for intermittent and frequent pumping operations

Disadvantages of Self-Priming Pump

  • The pump can’t run without starting priming fluid in the pump tank.
  • This type of centrifugal pump can be larger than the standard model due to the need for a reservoir, which can generate problems in services with limited space.
  • This pump can’t operate dry.

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