Slurry Pumps vs. Water Pumps: Why Do I Need A Slurry Pump?
When it comes to slurry transportation, familiarity with pumps and their parts is par for the course. However, it’s also important to understand what goes into each element of slurry transport. That understanding starts with a few basic questions: “What’s the difference between a slurry pump and a water pump?” “What makes a slurry pump special?” and “What kinds of slurry pump installations are there?”
Slurry pumps versus water pumps
What distinguishes slurry from other fluid types is the presence of a solid — gravel, copper, or sand — within a liquid. Although, in many cases, that liquid is water, a slurry may contain solvents, like acids, alcohols, or petroleum. Those non-water components, whether solids or solvents, make slurry pumps necessary.
In contrast to water pumps’ narrow and often inexpensive components, large replaceable slurry pump parts are made of sturdy, often specialized materials. These parts allow pumps to move nearly any type of solid within a slurry efficiently and safely. Water pumps, on the other hand, lack the hydraulic capacity to move solid particles and are unable to withstand the particle abrasion and chemical corrosion that slurries can cause.
What makes slurry pumps special?
Slurry pumps can withstand extensive wear due to characteristics such as: a large impeller diameter, shafts, bearings, and internal passageways as well as heavy-duty construction. On an industrial level, slurry pump features generate higher upfront and operational costs compared to water pumps. However, only slurry pumps can hydrotransport solid materials efficiently, and the long-term benefits outweigh initial costs.
Centrifugal force pushes something outward when it's spinning rapidly around a center.
Key to slurry pump success is the generation of centrifugal force, which pushes material outward from the pump center. This contrasts with centripetal force, which pushes material toward the center. Slurry pumps must operate on centrifugal principles because the forces that impart velocity to the slurry accelerate the transport process. A centripetal pump, on the other hand, would be impractical since the solids within the slurry would accumulate instead of flowing freely.
Slurry pump installations
Knowing these basics, it’s also important for anyone looking to install a slurry pump to understand the specific environments required for each type of pump. Three types of slurry installations exist:
Wet — In this installation, the slurry pump and drive are fully submersible. This is necessary for certain slurry pump applications, such as underwater operations.
Dry — In this installation, the pump drive and bearings are kept out of the slurry. The wet end — which includes the shell, impeller, hub or suction liner, and shaft sleeve or stuffing box — is free-standing and clear of any surrounding liquid. Slurry pump technicians install most horizontal pumps this way.
Semi-dry — This special arrangement is used for dredging applications with horizontal pumps. Operators flood the wet end and bearings but keep the drive dry. Bearings require special sealing arrangements in this case.
Although this guide provides an overview of slurry pumps and their installations, there’s plenty more to learn. For those who want to better understand slurry pumps and their applications or need help deciding which pump and installation type is best for their applications.
Top 8 Considerations for Selecting a Slurry Pump
Top 8 Slurry Pump Considerations
The following is a list of 8 considerations for choosing a slurry pump best suited for a slurry application. Selecting a pump for a slurry application is more difficult than for an application involving thinner fluids. If a mistake is made in the pump selection process, the pump chosen will most likely not work well, or will not pump the higher viscosity, abrasive, heavy, solid laden fluid at all, which renders the new pump useless!
Know the Material or Fluid Being Pumped
The fluid or material type and its characteristics are among the most important considerations. Is it a slurry, mud, sand, etc.
Fluid viscosity of the material, usually measured in centipoise (CPS).
Density of fluid, usually measured as specific gravity (Sg)
The pH level, which is the measure of hydrogen-ion concentration.
Static and operating temperature of the fluid.
Pump Flow Rate
Flow rate is another important factor for selecting the best-suited pump for a slurry application. The pump must be capable of exceeding the required flow rate to ensure desired flow rates are achievable (example of flow rate: 350 GPM or 200 cu. yards per hour {cu-yd/h}).
The flow rate of the pump must not only achieve the required flow rate of the application, but it must also be more than something called the critical flow rate. The critical flow rate is the constant flow rate required to maintain the suspended particles and solids in the slurry. Maintaining suspension of particles and solids helps to avoid the heavy portion of the fluid from settling at the bottom of the wetted path, as well as from settling at the bottom of the discharge piping.
Flow velocity is a critical consideration; the material must move at a consistent velocity through the piping to keep the slurry, particles, and solid-laden material suspended so it does not settle and cause clogging.
Materials of Construction
The materials that the pump is made of are necessary because the pump must be chemically compatible with the fluid being pumped. If the pump’s materials of construction and the liquid are not consistent, it can cause the pump to either melt down or crack, resulting in catastrophic failure of the pump, and can also cause damage to the immediate area surrounding the application and cause injury to workers.
The pump must also handle the abrasive characteristics of the fluid being pumped. If not, abrasive fluids can scour through the pump casing and cause premature wear of the internal pump components such as the rotor or impeller.
Inlet & Discharge Pipe Considerations
Pipe length, diameter, and the type of material of the piping are essential factors that are often not strongly considered when constructing a pumping system.
Pipe length is essential because the more significant the size of the pipe, the more fluid or material build-up will occur, requiring a more substantial amount of motor power to enable the pump to continue pushing the fluid or material to its final destination.
Pipe diameter should be sized considering two factors, reducing discharge head pressure and maintaining sufficient fluid or material velocity to avoid clogging of the discharge pipe. Regarding both reducing discharge head and maintaining adequate fluid velocity, the rule of thumb is to go more extensive on the pipe diameter, which will help to alleviate the adverse effects of both factors.
Pipe material should not only be chemically compatible with the fluid or material being pumped, but when selecting piping that has a reduced surface finish at the inside of the piping, it can also minimize pipe friction loss which can result in less energy required to pump the fluid or material to its final destination. The surface finish measure is denoted as Ra, which stands for Roughness Average.
Motor Power
Motor power, usually indicated by horsepower (HP), is important on any pump but wildly when pumping slurries and fluids with high specific gravity and viscosity because thicker, heavier fluids require a more significant amount of power and force to move the fluid or material to the desired final location.
The motor power must also be sufficient enough to overcome any forces within the discharge piping downstream of the pump. These forces within the discharge piping could be a result of pipe components such as tees, bends, and upward grades that create something that is referred to as discharge head pressure which is measured in PSIG.
Pump Operating Cost
Another important consideration that most pump user does not think about is the cost and economic impact of the pump. Having the best-suited pump for an application also includes how much money it requires to keep that pump running for whatever duration it is in service. It not only has the energy the motor uses but also involves selecting a pump that can move viscous material with low amounts of water or accompanying fluids.
Water and accompanying fluids used to make pumping viscous solid laden material possible can cost a lot of money. If these fluids can be reduced, it can save thousands of dollars on operating expenses.
Pump Elevation
The pump must be located in a manner that does not hinder its operation of the pump. In applications where the pump is positioned above the fluid to be pumped, the pump cannot be located higher than the pump’s ability to draw the liquid into the pump intake. If the pump is positioned at an elevation that is greater than the pump’s ability to remove the fluid into the pump, the result will be that the pump will not achieve prime, and the desired flow rate will not be reached, or even worse, the pump will not pump the fluid at all.
Pump Orientation
One last point to mention is pumped orientation. Pumps can be purchased with several different orientation options. The most common are vertical and horizontal, which refers to pump shaft orientation. Depending on the specific application, vertical and horizontal pump orientations can be the better choice. Horizontal orientation is the most purchased orientation, but vertical orientation can be better suited when a pump is used in a smaller space.
4 Types of Slurry Pumps and Their Uses: Which Is the Best?
Slurries are specialised compounds found in various processing industries, combining both solids and liquids’ properties. Various industries classify slurries depending on how aggressive they are. Some may be more aggressive than others, which is why it’s essential to choose the right pump in transporting them.
Meanwhile, a slurry pump is a kind of centrifugal pump that increases the energy of a solid-liquid mixed medium under the centrifugal force, converting the electric energy into kinetic energy and potential energy of the medium. There are various types of slurry pumps available in the market. But which among those types are best for your needs?
Horizontal Slurry Pump
A horizontal slurry pump has its shaft parallel to the horizontal plane, hence its name. It is a single-stage, single-suction axial suction, cantilever horizontal centrifugal pump with a high-strength and wear-resistant materials for the overflow parts. The horizontal slurry pump is most suitable for conveying strong abrasion, high concentration, corrosive significanceand fine particle slurry. It’s often used in metallurgy, mining, electrical power, coal mine and other industries to transport abrasive slurries.
Vertical Slurry Pump
Unlike the horizontal slurry pump, the vertical slurry pump is often used in slurry pools. The pump head should be submerged below the liquid—also why it’s called a submerged slurry pump. However, not all vertical slurry pumps are submerged underwater. It depends on the motor and the non-pump head compartments. It’s often used in conveying corrosive, coarse particles and high concentration slurry.
Submerged Slurry Pump
The Submerged Slurry Pump is a vertical single-stage single-suction cantilever centrifugal pump, and the impeller is a semi-open impeller. A mixing blade is arranged at the suction edge extension of the impeller. Its main selling point is the length of its pump shaft in the submerged part, reaching 800 to 2000 millimetres. It is mainly used in municipal engineering, paper mills, cement plants, printing and dyeing plants.
Submersible Slurry Pump
Last on the list is the submersible slurry pump. It is the coaxial integration of the pump and the motor. Its main selling point is there is no need to build complex fixtures and protective measures on the ground. It can be quickly submerged into the slurry and allow to do its job. Since a mechanical seal protects the motor, it prevents high-pressure water and impurities from entering the motor cavity. The submersible pump is most suitable for conveying slurry containing abrasive particles, such as sand, cinder and tailings.
How To Select the Right Slurry Pump
Selecting the correct type of slurry pump should be based on four factors: performance, material conveyed, sealing type and transmission mode. However, it can also depend on other factors, such as on-site working conditions and the acidity or alkalinity of the slurry.
It’s crucial to know about all these things to ensure that the chosen pump works along with its limits, providing superb performance and work satisfaction. There are four types of pumps for a reason—there are varied slurry types.
Conclusion
Selecting and operating a slurry pump can all vary based on various factors that play on-site. It’s a complex task due to how difficult it is to balance the pumps available in the market. However, try to consider the flow, pressure, viscosity, abrasiveness, particle size and particle type of the slurry you’re dealing with. If you need more help, an applications engineer should help you consider these factors to help you navigate for the best pump for the project.
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