What is a Self Priming Pump?

Pumps play a crucial role in moving liquids, but many standard pumps cannot start pumping if they have air inside.

Normally, a pump needs to be ‘primed’, which means its casing is filled with liquid before operation.

If a pump starts dry, it may just spin without moving fluid and can even be damaged.

Self priming pumps were developed to solve this problem.

A self priming pump is engineered to prime itself – it can automatically expel air from its intake and draw in liquid without manual help.

In simple terms, it’s a pump that starts pumping on its own, even when placed above the liquid source.

What is a Self Priming Pump?

Grundfos CM Self Priming Pump. Image credit: GrundfosA self priming pump is a type of pump that clears air from its system and begins pumping liquid without external assistance.

Traditional centrifugal pumps need to be filled with liquid before starting, otherwise they will only spin air and fail to move any water.

Self priming pumps are designed to overcome this limitation with special internal structures that handle air.

These pumps usually have a casing that holds some liquid, along with features like check valves and internal circulation paths that help evacuate air.

When switched on, the pump uses stored liquid to mix with air, creating a vacuum that pulls water up into the pump.

This design makes them ideal for above-ground applications or for lines that frequently draw in air.

What is a Self Priming Pump Used For?

Self priming pumps are used in a wide range of applications where quick and reliable pumping is needed.

These include:

Domestic and Commercial Water Transfer

They are used to move water between tanks, drain flooded basements, and empty containers.

Industrial Processes

In factories, self priming pumps are employed to transfer liquids, including chemicals and waste.

They’re also used in cleaning systems such as CIP (Clean-In-Place) setups.

Agricultural Irrigation

Farmers use self priming pumps to draw water from wells, rivers, or reservoirs to irrigate fields.

Their ability to handle air makes them dependable for intermittent operations.

Construction Sites

They remove water from excavations and trenches.

These pumps are often mobile and ready to use without manual priming.

Wastewater and Sewage

Self priming pumps can handle dirty water with some solids, making them useful for sewage handling or wastewater systems, such as pumping stations. .

How Does a Self Priming Pump Work?

A self priming pump works by using a clever internal design to remove air from the system and draw liquid into the pump.

It starts with a specially shaped casing or priming chamber that retains a certain amount of liquid even when the pump is turned off.

This retained liquid plays a vital role in the priming process.

When the pump is switched on, the impeller spins and mixes this stored liquid with any air present in the suction line.

This air-liquid mixture is circulated and directed towards the discharge outlet.

As the air is pushed out of the system, the internal pressure within the pump drops, creating a vacuum.

This vacuum draws more liquid from the source up through the suction pipe, gradually replacing all the air.

Once the casing is filled entirely with liquid and no air remains, the pump is considered primed.

It can now operate like a normal centrifugal pump, continuously moving fluid.

To maintain its self priming ability, many pumps feature a check valve at the inlet.

This valve stops liquid from draining out when the pump is off.

As a result, the pump stays partially full and can reliably self-prime again at the next startup without manual intervention.

Self Priming Pump Types

Self priming pumps come in various types, each designed to suit different fluids, pressures, and applications.

Choosing the right type depends on what is being pumped and where the pump will be used.

Self-Priming Centrifugal Pumps

These are the most widely used type of self priming pump.

They operate like standard centrifugal pumps but have a modified casing that retains liquid after shutdown.

This stored liquid allows them to prime themselves on the next start.

They are ideal for clean or slightly dirty water, making them popular for water transfer, irrigation, and general-purpose pumping.

Trash Pumps

Trash pumps are built to handle dirty water containing solids such as mud, sand, and debris.

They have large, tough impellers and wide internal passages to prevent clogging.

These pumps are commonly found on construction sites, in mining operations, and within sewage or stormwater systems.

Jet Pumps

Jet pumps combine a centrifugal pump with a venturi nozzle (jet) to create suction.

They are often used to draw water from shallow wells.

These pumps are common in domestic water supply setups.

Diaphragm Pumps

Diaphragm pumps move fluid using a flexible diaphragm and are naturally self priming.

They can handle thick fluids, chemicals, slurries, and even abrasive materials.

Diaphragm pumps are widely used in chemical processing and wastewater treatment.

Rotary Vane Pumps

These pumps use rotating vanes to create suction.

They are good for light fuels, lubricants, and oils.

Often found in mobile fuel systems or low-viscosity applications.

Liquid Ring Pumps

These pumps use a rotating impeller inside a liquid-filled ring to compress air and move fluid.

Suitable for liquid-gas mixtures in chemical plants.

Peripheral (Regenerative) Pumps

These pumps generate high pressure at low flow using a special impeller design.

Ideal for small systems where some air or gas is present.

Piston (Reciprocating) Pumps

These pumps use pistons to move fluid.

They’re best for high-pressure uses like firefighting or jet washing.

Many are self priming by design.

Self Priming Pump Advantages

Self priming pumps provide several key advantages that make them highly valued in a wide range of industries and applications.

No Manual Priming Needed

Once properly installed and initially filled, self priming pumps can clear air from their casing and suction line automatically at startup.

This eliminates the need for manual priming each time the pump is used.

It’s particularly useful in remote or hard-to-access areas where repeated manual effort is not practical.

Handles Air in the Line

These pumps are designed to tolerate and expel air that enters the suction line.

By removing air automatically, they prevent problems like air locks and dry running, helping to maintain a steady and reliable pumping operation even under variable flow conditions.

Fast Startup

Because there’s no need to manually fill the suction pipe before operation, self priming pumps start quickly.

This rapid response is critical in emergency applications such as firefighting or flood control, where every second counts.

Versatile

Self priming pumps can move a wide variety of liquids, from clean water to dirty fluids, slurries, chemicals, and even some solids, depending on the model.

This makes them ideal for use in agriculture, construction, industry, and municipal systems.

Flexible Installation

They can be mounted above the liquid source, which simplifies setup and avoids the need for deep excavation or submerged equipment.

Safer Maintenance

Being installed at ground level means the pump is easier and safer to maintain, reducing risks and saving time during service tasks.

Self Priming Pump Disadvantages

DAB Jet 151 MP. Image credit: DABWhile self priming pumps offer many advantages, they also come with a set of limitations that should be considered before selecting them for a specific task.

Higher Initial Cost

Self priming pumps are generally more expensive than standard pumps.

Their added features and more complex construction result in higher manufacturing and installation costs.

However, this can often be offset by long-term savings in labour and downtime.

More Complex Design

These pumps include additional parts such as check valves, recirculation passages, and specially shaped casings.

While these allow for self priming functionality, they also introduce more components that require regular inspection and maintenance.

Lower Efficiency

The internal design compromises needed to support self priming can slightly reduce hydraulic efficiency.

This means they may use more energy to deliver the same flow compared to a standard centrifugal pump.

Limited Suction Lift

Self priming pumps typically lift water only up to 7 or 8 metres.

When working close to this maximum, the priming process may slow down or fail entirely, especially if conditions are less than ideal.

Sensitivity to Debris

Standard self priming centrifugal pumps may struggle with large solids.

If debris is expected, trash or diaphragm models are better choices.

Requires Initial Liquid Charge

These pumps cannot start dry.

They must retain liquid or be filled manually before the first use.

Not Ideal for All Fluids

Highly viscous or sticky fluids can make it difficult for the pump to purge air, slowing or preventing successful priming.

How is a Self Priming Pump Different from a Non-Self Priming Pump?

Self priming pumps and non-self priming pumps serve similar purposes but differ in how they operate, especially at startup.

Priming Needs

A non-self priming pump must be manually filled with liquid before it can begin to move fluid.

If air is present in the suction line, it will fail to operate correctly.

A self priming pump, on the other hand, automatically removes air from its casing and suction line.

This allows it to prime itself and begin pumping without manual effort each time it starts.

Design Features

Self priming pumps are built with additional components such as priming chambers, check valves, and internal recirculation paths.

These allow them to retain some liquid after shutdown and create suction during the next startup.

Non-self priming pumps have a simpler design with fewer internal elements, focusing purely on efficient liquid movement.

Efficiency

Standard pumps are often more energy-efficient because they do not include the added flow paths needed for self priming.

However, self priming pumps are more flexible, especially in variable or remote locations.

Maintenance

Fewer parts in a standard pump mean easier maintenance.

However, self priming pumps require less attention in terms of manual priming, which can save time and effort in hard-to-reach installations.

Cost

Self priming pumps tend to cost more upfront, but their convenience and reduced labour requirements can make them more economical over time.

Self Priming Pump Alternatives

In situations where self priming pumps are not suitable or practical, several alternative solutions are available.

Submersible Pumps

These pumps operate fully submerged in the liquid.

Since they are always below the fluid level, they do not require priming.

Commonly used in wells, sumps, and flood control, they are ideal for continuous operation.

Vertical Immersion Pumps

With their impeller located below the fluid surface and motor above, these pumps remain primed naturally.

They are well suited for handling aggressive or hot liquids found in industrial processes.

Foot Valve Systems

A non-return foot valve at the end of the suction pipe helps retain water in the line.

This allows standard pumps to remain primed between uses, but the valve must be well maintained to prevent leaks.

Priming Tanks

These small external tanks keep a reserve of liquid near the pump, making them helpful in systems with intermittent flow.

Vacuum-Assisted Systems

Often used in larger industrial setups, these systems include a separate vacuum pump or ejector to remove air before startup, enabling reliable priming.

Conclusion

You should now have more of an understanding of self priming pumps.

A self priming pump is a smart solution to the age-old problem of priming.

It automatically removes air, draws in fluid, and begins pumping with minimal effort.

This makes it ideal for use in industries like construction, agriculture, wastewater management, and emergency services.

We’ve seen that these pumps come in many types, each suited to different needs.

Their advantages include fast startup, flexible installation, and reduced maintenance in hard-to-reach areas.

However, they are more complex, slightly less efficient, and usually cost more upfront.

Choosing the right pump depends on the job at hand.

For many tasks, especially where the pump sits above the liquid source or may deal with air in the line, a self priming pump is the best choice.

By understanding how they work and what they offer, you can make confident decisions and keep your operations running smoothly.

For more information, get in contact with us here at KD Pumps.