What Are Self-Priming Pumps?: Learn The Benefits Of Self-Priming Pumps.

What is a Self-Priming Pump, and how does it work?

Self-priming pumps are a type of pump that can automatically prime themselves without the need for external priming. They are commonly used in applications where the pump needs to be able to start and operate without manual intervention. Self-priming pumps are efficient and reliable, making them suitable for various industries and applications.

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Centrifugal pumps which have the capability to pump mixtures of liquids with entrained gas, as well as liquids, which have the ability to vent the suction line of air, are deemed to be self-priming pumps. 

Self-priming pumps operate by fluid recirculating within the pump head, which creates a vacuum. This causes air to be evacuated from suction pipework, until fluid enters the impeller of the pump.

The design of self-priming centrifugal pumps reduces pump efficiency to some extent, due to the separation chamber within the pump head which works when fluid is retained within the pump head to effectively create a vacuum.

There are some designs of pumps which are classed as self-priming which include progressing cavity, gear, peristaltic, side channel, peripheral and diaphragm pumps due to their positive displacement design, which are designed for fluids more or less viscous than water such as oils, foodstuffs, solids, some types of fuel, and chemicals.

Standard centrifugal pumps can also be made self-priming with the addition of a check valve being placed at the bottom of the suction pipework providing the casing is filled with water on startup. This prevents the water from draining out of the suction pipework. A pump operating in this fashion is known to create a manometric suction lift.

Differences Between a Self-Priming Pump and Other Pump Types

Units which are unable to self-prime are incapable of venting suction lines containing air meaning if pumps are located above tanks, pits or have long suction lines they cannot draw fluid to their inlet.

Non-self-priming pumps should have their suction flooded either:

• Via the use of a tank designed to supply the pump with sufficient fluid pressure at the inlet

• Suction pipework contains valves to ensure that the pump head and suction line remains filled with liquid

• A booster pump to ensure fluid at sufficient suction pressure enters the unit.
  

Applications for Self-Priming Pumps

Self-Priming pumps can be used in a variety of applications, here are a few examples along with some of our previous projects:

ATEX Fluid Transfer &#; Rather than having an ATEX submersible pump immersed in a flammable liquid, having a surface mounted pump which primes from pits can be far safer, and lead to fewer issues as the motor and cable glands are not immersed within the flammable liquid. One ATEX self-priming pump we provided in the past was for a distillery to bulk transfer Methanol at 95% concentration.

Pit Emptying &#; Units are great at pit emptying eliminating the need for confined space entry.

Solid Handling &#; Such designs are typically engineered to handle solids and can often transfer these comfortably. One of our previous projects that required solid handling was for a wheel wash system at a quarry.

Wastewater Handling & Dewatering &#; Units can be kept in situ with hoses ported around site for dewatering various areas rather than having to relocate pumps each time an area needs dewatering saving time, labour, and resources.

Tanker Offloading &#; Self priming pumps ensure that tankers, and storage tanks are stripped of fluid, maximising fluid transfer as well as eliminating vapour locking in suction lines.

Varying inlet / Tidal Conditions &#; For transferring from tidal rivers or the sea to on land, having a pump which can handle fluctuating intake conditions can help eliminate any possible issues caused by changes in fluid suction height.

9 Factors to Consider When Selecting a Self-Priming Pump

Before selecting the an application there are a few key factors you should consider:

1. Size of Solids &#; To ensure the impeller can sufficiently handle any particles without clogging.

2. Fluid Viscosity &#; This often determines pump speed, possible flow rate and if other devices are required such as a follower plate to help feed the pump.

3. Priming Distance &#; Not just the horizontal, and Vertical runs of pipework but also any accessories such as bends, strainers or valves which can add pressure losses and determine possible priming distance.

4. Fluctuating Fluid Levels &#; If water is being drawn from the sea, tidal rivers, or tanks where water levels change, care must be taken to ensure that the designed flow is possible at various heights without encountering issues due to a lack of suction pressure such as vortexing or cavitation due to insufficient NPSHA.

5. Priming Time &#; That the time taken to evacuate the suction pipe is checked and that the unit does not overheat or take too long to start up. During priming, fluid recirculates within the casing, creating a vacuum. As it recirculates it begins to heat up, and if left too long, it can heat above the temperature rating of gaskets and seals within the pump head.

6. Power Options &#; How to power the pump whether it be by single, or 3 phase, hydraulically driven or by engine.

7. Close Or Long Coupled &#; Whether a cost-effective unit is required or a robust long coupled unit.

8. Trailer Mounted, Baseplate or Pontoon Mounted &#; Whether your pump will stay in situ, require a trailer for portability across your land / domestic roads or installed on a pontoon for dewatering there are many options to consider.

9. Controls &#; How the pump will start, stop, and operate as part of your system, and whether certain events may be triggered.

Advantages of Self Priming Pumps

There are many advantages to self-priming pumps, but also some drawbacks:

Entrained Gas Handling &#; Due to their ability to vent suction lines they can handle fluids with entrained gasses, priming for up to 30 mins without drawing liquid.

Easy to Maintain &#; They are far easier to maintain than a submersible pump which is immersed in the liquid and may need confined space training to maintain.

Reliable &#; Their designs are not based on use with other accessories meaning they do not rely on additional valves to function which can sometimes fail

Robust &#; As the motor and cable are not immersed in fluids, they are longer lasting and less exposed to pumping mediums when handling corrosive or aggressive fluids

Disadvantages of Self Priming Pumps

Efficiency &#; Self-priming pumps tend to be less efficient than standard centrifugal pumps due to their internal volute and solid handling, meaning internal clearances are larger with a corresponding increase in energy consumption.

Priming &#; Units can need to be reprimed or have the casing filled with fluid prior to startup in particular if stood idle for long periods of time. Suction lines may also need to be checked to ensure the pump can empty suction lines of air in the time required.

Clogging &#; Pumps may still require suction strainers to prevent clogging, and not all designs can handle solids.

Maintenance Tips and Troubleshooting

As with any pump it is always essential to keep a set of spare parts locally on site.

As a way of pre-empting any issues conduct the following:

Visual Inspection &#; Visually inspect the pump for any leaks, damage or unusual sounds indicating there is an issue present. Open the inspection port to check the impeller rotates freely and that there are no foreign particles present.

Lubrication &#; Ensure any bearings are adequately lubricated, or constant level oilers have sufficient lubricant.

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Vibration / Alignment &#; Check pump is aligned, and that excessive vibration is not occurring.

Maintenance Log &#; Always keep a maintenance log local to the unit to detail what maintenance was done when.

If you're experiencing issues with your self-priming pump read our troubleshooting guide for some of the most common issues, alternatively we are always available to discuss any current issues.

How to install self-priming pump

Self-priming pumps should first have the casing filled with liquid via the priming port prior to startup.

All suction lines should be thoroughly checked for air leaks, and the discharge line should not only be free from obstruction but also not contain any non-return valves directly above the pump on the discharge which can prevent the pump from evacuating any air.

The unit should be started and observed to ensure it does not vibrate excessively, that all noises are normal and that that the unit is not cavitating.

The pump should be run to check it successfully primes, operates without issue, and is performing as per its curve. The pump should be started and stopped several times to ensure it reprimes without issue.

Why Choose Our Self-Priming Pumps

Our self-priming centrifugal pumps are unlike other designs as they are built with an armoured volute, which protects the main casing from abrasive wear, and high velocity solid impact.

Constructed in ductile iron, along with the impeller, it ensures that units are durable, handle solids up to 50 x 24mm in diameter without loss of flow and last for many years to come.

For more information contact our experts today, they can help resolve any issues you might be having or begin your journey on getting a new application installed.

February 22nd,

What is a Self-Priming Pump, and How Does it Work?

Self-priming pumps are a specific type of liquid pump designed to have the required liquid inside the cavity or pump body necessary to start the pumping process. This offers the potential for increased operating efficiencies in process plants where pumps are used for a variety of repeated yet intermittent operations. 

In the sanitary and hygienic processing industries, self-priming pumps are incorporated into process lines to perform several different tasks.

Pumps are used to:

• Move products through process lines
• Pump CIP (clean-in-place) fluids to clean and sanitize pipes and components
• Transfer liquids from one storage vessel to another
• Empty tanks and drums

Some pumps are designed to always have the requisite start-up liquid in the pump&#;s chamber or body. These are called &#;self-priming&#; pumps. Other pumps require the start-up liquid be added to the pump before initiating operation. This process, known as manual priming, involves external methods and can be labor-intensive. No one type of pump is intrinsically superior to another: it simply depends on what the pump is used for and how often.

Types of Self-Priming Pumps

There are several types of self-priming pumps available, each designed to handle specific fluids and operational conditions:

• Positive Displacement Pumps: Utilizing a piston or diaphragm, these pumps move fluid through the pump with precision. Self-priming positive displacement pumps are particularly effective for viscous fluids or those containing solids.
• Diaphragm Pumps: These pumps employ a flexible diaphragm to move fluid, making them suitable for handling corrosive fluids or those with solids.

Each type of self-priming pump offers unique advantages, making them suitable for a wide range of industrial and commercial applications.

How a Self-Priming Pump Works

Some types of pumps are engineered to be automatically self-priming. Pumps of this nature feature close tolerance working parts that trap fluids in the pump&#;s body, preventing them from returning from the discharge side of the pump to the suction side when the pump is not in operation.

In these types of pumps, the constant presence of fluid in the pump&#;s body allows the pump to better handle what are called &#;air pockets&#;. Air pockets are an accumulation of air bubbles in the pump&#;s working mechanism, which can impair proper pump operation.
 

Most liquid pumps used in the sanitary processing industries are centrifugal-type pumps. Centrifugal pumps are:

• Simple
• Sturdy
• Relatively inexpensive
• Ideal for pumping water and other low viscosity fluids such as CIP solutions under circumstances where suction conditions are difficult

For these types of low viscosity fluids, a V-type centrifugal pump design is often preferred, featuring a vacuum pump and positive seal that is located close to the discharge port. This allows a V-type centrifugal pump to readily pull a vacuum until it is full of fluid.

However, standard centrifugal pumps are not designed to be self-priming. Unlike the pump types already described, standard centrifugal pumps do not trap liquids when not in use &#; although engineered modifications to the pump&#;s housing, such as surrounding the pump with a tank and ensuring it remains immersed in liquid, may allow some of these types of pumps to be self-priming.

With centrifugal pumps, the pumping action occurs when an impeller is rotated in a liquid within a cavity or chamber of the pump, displacing the liquid and forcing it to flow into the discharge port of the pump via centrifugal force.

Fluids typically enter the pump at the center of the impeller and are discharged via a port on the outer perimeter of the pump&#;s body. The impeller is often directly coupled to the pump&#;s motor, in what is called a monoblock design.

Air is the primary enemy of this type of pump. The pump casing plays a crucial role in maintaining pressure and ensuring proper operation. When a standard centrifugal pump encounters air pockets, it can become &#;air bound&#;, and refuse to operate. Air intrusion into standard centrifugal pumps is typical, as these types of pumps don&#;t feature tightly coupled pumping mechanisms such as gears or screws and have no seals between the suction and discharge sides of the pump. The pumped fluid is essential for lubrication and cooling of the pump's bearings, and air presence can lead to air-binding.

Self-priming centrifugal pumps overcome air binding by initially mixing any residual air in the pump&#;s working mechanism with fluid during the priming process.

This blending allows the resulting mix to move readily through the pump&#;s body on initial start-up, removing the air and aiding product flow on the suction side of the pump. The process liquids and any entrained air move toward the impeller, and normal pump operations commence.

In comparison to a standard centrifugal pump, what&#;s notable in the design of a self-priming centrifugal pump is that it features a liquid reservoir built into the body of the pump, typically either above or in front of the impeller.

This reservoir allows the pump to rid the pump&#;s body and suction line of air during the priming cycle, replacing it with liquid from the reservoir that is blended into the residual air. The &#;self-priming&#; capability of this type of centrifugal pump comes from the ability of the reservoir to retain liquid after its very first prime.

Advantages of Self-Priming Centrifugal Pumps

• Can handle a variety of liquids
• Work well with slurries, corrosive liquids, and suspended solids
• When compared to submersible-type pumps, self-priming centrifugal pumps will continue to pump liquids even after the pump is no longer submerged in a liquid tank or vessel
• Ideal for frequent and intermittent pumping operations, as the steps involving pump priming on start-up are eliminated

Disadvantages of Self-Priming Centrifugal Pumps

Self-priming pumps have disadvantages, including lower efficiency, higher initial costs, and greater energy consumption.

• Can&#;t operate without the presence of the initial priming liquid in the pump&#;s reservoir
• Due to the need for a liquid reservoir, this type of centrifugal pump can be larger than a standard model, which may cause issues in applications where space is limited
• Need to be as close as possible to production lines to avoid depletion of the pump&#;s liquid reservoir during self-priming operations

An Overview of CSI Self-Priming Pumps

LKH Prime

The LKH Prime pump from Alfa Laval is a centrifugal-type self-priming pump that is ideal for CIP operations. The LKH Prime also easily pumps products with entrained air. Once the liquid no longer contains entrained air, you are left with a highly efficient and quiet LKH Pump, one of the most capable centrifugal pumps produced.

For product applications, this pump features an air screw coupled with a highly efficient centrifugal impeller to effectively handle a variety of process media.

The sanitary design incorporates wetted parts made from acid-resistant AISI (American Iron and Steel Institute) 316L stainless steel, with other components made from AISI 304 stainless steel. The LKH Prime is EHEDG and 3-A approved for sanitary applications.

SP Series

The SP Series is a liquid ring pump from Ampco that uses compression chambers to pump, and only uses centrifugal force to seal the chambers with a liquid. It is excellent for CIP return operations and pumping products with entrained air.

The SP Series pump is efficient at emptying tanks and drums, and can handle shear-sensitive products due to its tight manufacturing tolerances and unique impeller shape.

These pumps feature a 304 stainless steel adaptor and are in conformance with 3-A sanitary standards.

SLH Twin Screw Pump

Bornemann's SLH Twin Screw Pump is a self-priming positive displacement pump best for aseptic processes and applications involving high viscosities, high pressures, or sensitive materials. The variable speed feature of this pump is suited for varying operating conditions.

The Bornemann SLH Twin Screw Pump is EHEDG and 3-A approved for sanitary applications.

C-Series

The C-Series is an eccentric disc pump featuring Mouvex technology. This positive displacement pump uses its strong suction power and ability to run dry to gently and effectively move both liquid and dry products.

The C-Series is available in stainless steel models that carry 3-A approval and are designed to meet EHEDG specifications. This pump can be flushed and cleaned using CIP methods without disassembly and can pump both high and low viscosity products with outputs not affected by variations in liquid viscosity.