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How to select a slurry pump?

 

When handling slurries, users frequently must choose between rubber-lined or metal construction for their slurry pumps. This article presents some of the trade-offs and limitations related to the application of either of these two slurry pump designs. Table 1 at the conclusion of this article provides summary comparison of both designs.

Slurry is a liquid with suspended solids. The abrasiveness of slurry depends on solids concentration, hardness, shape, and the solid particle kinetic energy transferred to pump surfaces. Slurries may be corrosive and/or viscous. Solids may include particulate fines or larger solid materials that are frequently of irregular shape and distribution.

Determining the when to use a slurry style centrifugal pump can be a challenging decision. Often the cost of a slurry pump is many times that of a standard water pump and this can make the decision to use a slurry pump very difficult. One problem in selecting a pump type is determining whether or not the fluid to be pumped is actually a slurry. We can define a slurry as any fluid which contains more solids than that of potable water. Now, this does not mean that a slurry pump must be used for every application with a trace amount of solids, but at least a slurry pump should be considered.





Slurry pumping in its simplest form can be divided into three categories: the light, medium and heavy slurry. In general, light slurries are slurries that are not intended to carry solids. The presence of the solids occurs more by accident than design. On the other hand, heavy slurries are slurries that are designed to transport material from one location to another. Very often the carrying fluid in a heavy slurry is just a necessary evil in helping to transport the desired material. The medium slurry is one that falls somewhere in between. Generally, the Percent solids in a medium slurry will range from 5% to 20% by weight.





After a determination has been made as to whether or not you are dealing with a heavy, medium, or light slurry, it is then time to match a pump to the application. Below is a general listing of the different characteristics of a light, medium, and heavy slurry.



Light Slurry Characteristics:



• Presence of solids is primarily by accident



• Solids Size < 200 microns



• Non-settling slurry



• The slurry specific gravity < 1.05



• Less than 5% solids by weight



Medium Slurry Characteristics:



• Solids size 200 microns to 1/4 inch (6.4mm)



• Settling or non-settling slurry



• The slurry specific gravity < 1.15



• 5% to 20% solids by weight



Heavy Slurry Characteristics:



• Slurry's main purpose is to transport material



• Solids > 1/4 inch (6.4mm)



• Settling or non-settling slurry



• The slurry specific gravity > 1.15



• Greater than 20% solids by weight





The previous listing is lust a quick guideline to help classify various pump applications. Other considerations that need to be addressed when selecting a pump model are: Abrasive hardness



• Particle shape



• Particle size



• Particle velocity and direction



• Particle density



• Particle sharpness



The designers of slurry pumps have taken all of the above factors into consideration and have designed pumps to give the end user maximum expected life. Unfortunately. there are some compromises that are made in order to provide an acceptable pump life. The following short table shows the design feature, benefit, and compromise of the slurry pump.

 

SLURRY PUMP DESIGN
Design Feature
Benefit
Compromise
Thick Wear Sections
Longer component life
Heavier, more expensive parts
Larger Impellers
Slower pump speeds longer component life
Heavier, more expensive parts
Specialty Materials
Longer component life
Expensive parts
Semi Volute or
Concentric Casing
Improved pump life
Loss in efficiency
Extra Rigid Power Ends
Improved bearing lives
More expensive shafts and bearings





 



 

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