This article will take an in-depth look at centrifugal pumps.
The article will bring more understanding on topics such as:
This section will explore the fundamentals of centrifugal pumps, including their design, construction, and operational principles.
A centrifugal pump is a type of hydraulic device that transforms mechanical energy into hydraulic energy through centrifugal force applied to the fluid. It operates by rotating a component to impart velocity to the liquid, which is then converted into flow. The operation of a centrifugal pump relies on various mechanical parts working together.
This mechanical setup includes the pump's shaft, which is supported by bearings, a sealing system that prevents excessive leakage, structural elements designed to endure operational loads and stresses, and wear surfaces that allow the pump to be serviced and restored to its original condition.
Each pump should include the following components:
It is the central part of the pump which rotates together with the impeller when connected. The shaft is linked to the prime mover in order to get the power. The shaft fits perfectly with the ball bearing.
It consists of a series of backward-curved vanes attached to the shaft of an electric motor. This rotating element, known as the impeller, is housed within a watertight casing. As the impeller spins, it imparts velocity to the liquid.
This component is a sealed passage that encircles the impeller. Its design ensures that the kinetic energy imparted by the impeller is converted into pressure energy before the liquid exits the casing and enters the delivery pipe. The casing serves as a protective cover for the system, transforming the velocity generated by the impeller into a steady flow. There are three primary types of casings in centrifugal pumps: volute casing, vortex casing, and casing with guide blades.
This type of casing surrounds the impeller and features a design that progressively increases the flow area. This design reduces the velocity of the liquid while simultaneously increasing the pressure as it moves through the casing.
This casing consists of a circular chamber positioned between the impeller and the volute casing. The fluid exits the impeller and first enters the vortex chamber before proceeding to the volute casing. This design efficiently converts velocity energy into pressure and generally offers better performance compared to the volute casing.
This casing type features blades arranged around the impeller. These guide blades are designed to direct the water flow smoothly from the impeller, minimizing turbulence. As the water flows through the guide vanes, it passes through a gradually widening passage, which helps in converting the velocity into pressure before it exits through the delivery pipe.
The suction pipe has two terminals: one end is connected to the pump's inlet, while the other end is submerged in the water source, such as a sump. A foot valve is installed at the lower end of the suction pipe, designed to open only in an upward direction, thereby allowing flow in one direction only. Additionally, a strainer is placed at the end of the suction pipe to prevent foreign objects from entering the system.
The delivery valve features two ends: one end connects to the pump's outlet, while the other end is responsible for delivering the water to the desired height or location.
Choosing the right materials for centrifugal pumps involves considering several factors: strength, resistance to abrasive wear, corrosion resistance, casting and machining characteristics, ease of repair and welding, and overall cost.
Centrifugal pumps are manufactured using a variety of materials, including cast iron, cast steel, stainless steel, bronze, brass, carbon structural steel, composite materials, alloy steel, and non-metallic substances.
When selecting materials for centrifugal pumps, consider the following factors:
Centrifugal pumps come in various types, including:
These pumps run on 12 V DC and offer a maximum flow rate of 330 GPH. They come equipped with alligator clips, a battery cable, and an on/off switch for easy operation. The pump can handle water heights as low as 1/8 inch with the suction strainer and lift water up to 40 feet. It includes a 3/4 inch garden hose adapter at both the inlet and outlet, a 6-foot suction hose, a replacement gasket, and an extra impeller. The pump's lightweight design allows for portability, and a carrying handle can be attached for added convenience.
Chemical pumps are designed specifically for use in pumping chemicals that are resistant to corrosive materials, which makes it suitable for handling corrosive and abrasive industrial liquids such as paint, fuel, solvent, bleach, and many others. A pump that contradicts the chemical can result in brittleness or dissolving, swelling, and ultimately it will leak and fail. Special consideration needs to be given to the materials of a chemical transfer pump, along with the concentration and temperature of the fluid being handled. Whenever there is required a chemical dosing pump, one for tank to tank transfer or a barrel emptying pump, the pump can be tested.
Radial centrifugal pumps direct the fluid outward at a 90-degree angle from the impeller relative to the suction direction. These pumps are prevalent and feature a horizontal suction flange with fluid exiting through a vertical discharge flange. The discharge is perpendicular to the pump’s shaft. This design is typically chosen when there is a need to increase discharge pressure while managing flow limitations. Consequently, radial centrifugal pumps are characterized by low flow rates and high pressures. They are commonly used in industries such as gas and oil.
Axial flow centrifugal pumps allow the fluid to move parallel to the pump shaft, similar to how a propeller functions. These pumps are particularly suited for applications requiring high flow rates with minimal pressure heads. They are commonly used in water circulation and dewatering systems due to their ability to handle large volumes of fluid efficiently.
Mixed flow centrifugal pumps combine both axial and radial flow characteristics, providing a balance between the two types of pumps. This design allows mixed flow pumps to handle larger flow rates while achieving a moderate increase in pressure head. They offer versatility for applications requiring both significant flow and pressure.
In a single-suction centrifugal pump, fluid enters through the inlet and is guided towards the impeller eye, which serves as the entry point for the impeller. As the fluid exits the impeller, centrifugal force generates the necessary pressure.
When the flow rate becomes too high for single-suction pumps to handle effectively, double suction centrifugal pumps are employed. These pumps are designed with an impeller that allows fluid to enter from both sides, unlike the single-sided entry of a standard pump. Despite the name "double suction," the pump still has only one flange each for discharge and suction. The primary distinction lies in the design of the casing and impeller.
Centrifugal pumps with a single volute casing direct the fluid from the impeller into a single volute that encircles the impeller entirely. This volute features a single cut-water that channels the fluid towards the pump outlet. Single volute casings are commonly used in refinery centrifugal pumps.
Portable pumps designed for dewatering applications are often used to handle large volumes of water mixed with both soft and hard solids, such as mud, twigs, leaves, sand, and sludge. These trash pumps are typically heavy-duty centrifugal pumps with larger discharge openings and deeper impeller vanes compared to other types. They can process materials with suspended particulates that might clog other pumps and can move hundreds to thousands of gallons per minute. Trash pumps are constructed with large discharge openings and pump housings, and they are available in materials like cast iron, steel, aluminum, and stainless steel. Many of these pumps feature roll cages for added durability.
Semi-trash pumps are a variant with smaller openings and are not designed to handle large solids or high concentrations of solids. For rigorous pumping tasks involving solid-laden slurries or water, regular trash pumps are more appropriate. Trash pumps come in several types, including syringe pumps, progressive cavity pumps, sanitary pumps, and positive displacement pumps.
They are also known as deep well turbine pumps. These are vertical axis or mixed flow centrifugal pumps which include stages of stationary bowls and rotating impellers to process the guide vanes. Vertical pumps are used whenever the level of water pumping is below the volute centrifugal pump limits. Vertical pumps are costly and are more complicated to refurbish and fit. The design of the pressure head mainly depends on the impeller’s length as well as on the speed of its rotation. The pressure head designed with just one impeller is not that suitable. The different types of vertical pumps are:
Other related types of pumps include vertical sumps, vertical turbine pumps, process pumps, and industrial pumps.
The well pump plays a central role in a water well system by moving water upwards into the household or designated water system. Currently, jet pumps and submersible pumps are the most commonly used types. Both utilize centrifugal force to elevate water. Impellers, which are spinning rotors, create a vacuum that pushes the water up through the well casing and into the distribution system. The choice of well pump depends on the water needs of the household and the well’s depth.
Jet pumps are installed above ground and lift water from the well using a suction pipe, with an impeller generating a vacuum. This vacuum drives water through a small nozzle. Jet pumps need to be primed with water before they can function properly. Shallow well jet pumps are designed for wells up to 25 feet deep, while deep well jet pumps can handle depths of up to 150 feet.
Submersible well pumps offer a broad range of operational depths, making them suitable for wells as shallow as 25 feet and as deep as 400 feet. As their name implies, these pumps are installed below the water level within the well. Unlike jet pumps that draw water from above, submersible pumps primarily focus their energy on pushing water upward.
These pumps are typically cylindrical and include a pump motor along with multiple impellers to move water up through the pump and into the drop pipe. Due to their robustness, efficiency, and adaptability to varying well depths, submersible pumps are the preferred choice in most contemporary well systems.
This chapter will explore the uses and advantages of centrifugal pumps, as well as cover their maintenance procedures.
Centrifugal pumps are utilized in a variety of applications, including:
The advantages of centrifugal pumps are as follows:
Some of the limitations of centrifugal pumps include:
Maintaining centrifugal pumps includes the following tasks:
A centrifugal pump is a machine that changes kinetic energy into the fluid’s pressure head. The external power from a diesel generator or electric motor then turns the pump impeller. Under the influence of the centrifugal force, the fluid enters the impeller reaching its tip and leaving the volute casing. There are many types of centrifugal pumps for example chemical pumps, vertical pumps, and trash pumps to mention only a few. They can be classified according to flow type), based on the number of stages (single stage and multi-stage pumps), and also on the type of volute (single and double volute).
Maintaining the pump is easy; most of the measures are given in the manufacturer’s guide. If used and maintained properly the centrifugal pumps can last long and are less costly. Choose a pump that is compatible with what needs to be used for example when pumping hazardous chemicals, a chemical pump is advised.
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