What is a Slurry Transfer Pump?

Slurry transfer pumps are vital in many industries–from farming, abattoirs, biogas/anaerobic digestion to food processing and pulp and paper, they consistently pump viscous liquids with higher total solids to keep systems free from blockages and breakdowns.

Our comprehensive guide covers all the basics:

1. What is a slurry transfer pump?

2. Types of slurry transfer pumps

3. Key components and design features

4. How to choose aslurry transfer pump

5. Performance considerations

6. Maintenance and operational best practice

What is a slurry transfer pump?

Slurry transfer pumps are designed to handle liquids with high total solids and thicker liquids, such as sandy/gritty sludge, starch and manure. They are more rugged, easier to maintain and more cost-effective in heavy-duty applications than conventional pumps, which are not designed to withstand heavy wear and tear.

Slurry pumps are essential in many sectors of waste management, falling into various specific industries:

• Agriculture and Energy Production

Slurry pumps are a staple part of livestock farms, where liquid manure is pumped for applying on fields or transferred, including other systems such as separators.  They are also used to feed organic material into anaerobic digestion plants for green energy production.

• Mining, Dredging and Construction

Submersible and robust pumps clear muddy and sandy water away during mineral extraction or while completing groundwork. They are also used in land reclamation projects, where sand and sediment are dredged up from a waterbed to build up land in another area.

• Food and beverage manufacturing

Food-grade slurry pumps help to ensure consistency and quality in food and drink manufacturing, such as fruit pulps, sauces, batters and chocolate.

• Pulp & paper

In pulp and paper manufacturing, solids handling pumps are used to feed large quantities of water, fibres and wood pulp into systems in the same industry, they are required to pump by-products away for appropriate waste disposal.

• Wastewater treatment

For the treatment of both greywater and foul water, slurry pumps are used to transfer wastewater and raw sewage, which often contain a high percentage of fibrous and foreign objects that are wrongly disposed of in toilets.

Types of Slurry Transfer Pumps

There are two main types of slurry transfer pumps, centrifugal and positive displacement. Each has unique advantages and limitations that lend them to different applications.

Centrifugal Slurry Pumps

Centrifugal slurry transfer pumps consist of a volute in which a motor-powered impeller spins to generate centrifugal force. This forces slurry to the edges of the volute and out of the discharge, leaving a space of negative pressure within the pump body, which draws in more slurry to continue the pumping process.

Submersible and surface-mounted centrifugal slurry pumps are available depending on the needs of the application. Submersible centrifugal pumps generally do not require priming as they are installed within the medium they are pumping, whereas surface-mounted models require priming before they can start pumping, as they are typically installed above the slurry level.

• Higher flow rates
• More energy efficient
• Fewer moving parts, less wear and tear, lower maintenance costs

Positive Displacement Slurry Transfer Pumps

Rather than a rotating impeller, positive displacement pumps create a cycle of suction and discharge using a mechanical element, such as a piston, scroll or lobe that changes the volume/pressure within the pump body to continuously draw slurry in and force it out again.

Like centrifugal slurry pumps, positive displacement slurry pumps can be submersible or surface-mounted depending on the application.

• Generates higher pressure, better for handling viscous fluids
• More consistent flow rate, better for precise dosing

Key Components & Design Features

Impellers

Impellers are a key component in centrifugal slurry transfer pumps – they provide the force that moves liquid through the pump discharge, which in turn creates the pressure difference to draw in more slurry and continue the pumping process. There are three main kinds of impellers used in slurry pumps:

1. Channel impellers

Channel impellers are a high-efficiency impeller that is suited to pumping liquid with suspended solid particles. These impellers can have single or multiple channels through which liquids and solids pass.

Single-channel impellers have one large channel through which bigger solids can pass. Multi-channel impellers can have up to three channels, which makes them more energy efficient but reduces the solids handling capabilities.

Both single and multi-channel impellers also come in an open or closed configuration. Closed channel impellers, as the name suggests closed off on both sides, making them more energy efficient, but with reduced free passage for solid content 

Open channel impellers have an open front end, allowing for better free passage and with less risk of blocking. 

2.  Multi-vane impeller (high head)

Multi-vane impellers offer high efficiency whilst providing high head capabilities, ideally suited for pumping heavily laden liquid over longer distances

3. Set back vortex impeller (solids handling)

Vortex impellers consist of several vanes attached to a backing plate that create a whirlpool effect within the pump housing. These pumps typically have the impeller set back out of the liquid, which greatly decreases the risk of ragging.

Pump casing and liners

Pump casings are typically made from high-grade cast iron, options are also available for cast stainless steel or bronze for exceptional corrosion resistance in particularly tricky applications.

Some surface-mounted pumps come with the additional benefit of wear plates/liners, giving a cost-saving when working with abrasive liquids

Shaft seals and bearings

Premium pumps are usually equipped with top-quality, branded bearings to provide long, uninterrupted service life. On particularly heavy applications, it is also common to find oversized bearings for optimum longevity

Premium pumps are often equipped with top-quality mechanical seals, with most now installed with dual seals housed within an oil bath.  This gives greater protection to the mechanical seals and allows for long, continuous running. 

Factors Affecting Pump Selection

Slurry Characteristics

• Percentage of total solid content present (TS)
• Type of solid suspended
• Viscosity of the pumped media
• Abrasive nature of the liquid

Abrasiveness and corrosiveness

Material of pump body, impeller and wear components needs to be strong enough to deal with the abrasiveness of solids and chemically compatible to deal without corroding.

T-T slurry pumps are made of high chrome cast iron, ductile iron, cast stainless steel, cast bronze and cast alloy – each material carefully selected to suit the application type.

• Viscosity

Positive displacement > centrifugal pump

Typically, waste water pumps will work with a total solid percentage of around 4-5%, with some specialist chopper versions capable of working up to 12%

Depending on the type, positive displacement pumps have the ability to work up to 30%, moving very heavily laden liquids.

• Temperature

Most submersible pumps have a maximum working temperature of 40°, whilst surface-mounted pumps can work up to 60°.

This is due to the submersible pump using the pumped media to cool the motor, whereas the surface-mounted version has an inbuilt motor fan.

Higher temperature tends to make viscous liquids thinner, which will affect flow rate and necessary pump power requirements

Flow Rate and Head Requirements

• Flow and head

The flow and head required depend on the needs of the application, and are usually advised by the client. Using the information provided by the client, our technical team can select the perfect pump for the application.   

The head relates to how high the pump can lift the liquid, with heavier/thicker liquids potentially requiring a more powerful motor. 

High head pumps tend to be selected for work on agricultural or quarry applications, as the head requirement is usually more demanding than that of wastewater sites.

-              Higher head and higher flow = more power needed, correct impeller selected.

-              Bigger inlet/outlet decreases head/pressure but increases flow and vice versa.

• Critical flow rate

Each pipe size has a minimum and maximum flow rate requirement and is part of the selection process undertaken by our technical team. 

The minimum flow rate for each pipe size ensures that the liquid is flowing quickly enough to keep the pipework clear, preventing solids from falling out of suspension within the pipe.

Exceeding the maximum flow rate for a certain pipe size can cause pipe hammer, which, over time, can cause damage to the pipework.  

Performance Considerations

Efficiency and Power Consumption

Higher efficiency = lower power requirement

Component choices can increase or decrease efficiency, e.g.

-              X impeller is more energy efficient, but cannot handle larger solids/more heavily laden slurries

-              Y impeller is less energy efficient but also more reliable for slurries with bigger/more fibrous solids.

What else affects efficiency and power consumption?

• Worn components
• Heavier liquid than advised
• Temperature of the pumped media
• Blockage within the pipework
• The incorrect pipe size for the pump is offered 

Maintenance and Operational Best Practices

Monitoring and Proactive Maintenance

Regular inspections of a pump can inform you of developing issues and inform you of a maintenance requirement to prevent a loss in pump performance or a complete breakdown:

• Inspect the pump impeller for visual signs of damage or wear
• Inspect the pump wear plate and pump casing for signs of damage or wear
• Inspect the mechanical seal oil for signs of contaminants
• Visual inspection of the cable for signs of damage
• Check for balance of the windings to ensure good motor health