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What is a water pump?
A water pump is a type of pump designed for transporting water. The water transported could be clean, fresh, and salty or water with solid particles like wastewater or sewage. Water pump manufacturers always specify the type of water the pump can transfer. A water pump creates a vacuum that draws water from its source into the pump. The pump has internal parts that, when they move relative to each other, causes water to gain high-pressure energy. The high-pressure energy moves the water from the pump to your desired location. There are two main categories of water pumps: centrifugal pumps and positive displacement pumps. Centrifugal water pumps use centrifugal force to move water, while positive displacement pumps use displacement motion. Each type of pump has its unique advantages and disadvantages.
Figure: Centrifugal water pump.
How does a water pump work?
All water pumps use a similar working principle. The working principle employs the force of nature. This force helps to move the water from its source into the pump. Water pump manufacturers design each pump with a specific moving part such as an impeller, vanes, gear, or piston. When you turn the pump on, internal parts start moving. This motion moves air out of the way. The movement of air creates a vacuum (a state of low pressure relative to atmospheric pressure) in the pump. This vacuum forces water to move from its storage tank into the pump. When the water gets into the pump, it gains more kinetic and pressure energy. The pressure energy helps the water to move from the pump into the required location.
Figure: Working of a centrifugal water pump and positive dispalcement water pump
Types of water pumps
Water pumps are of two main types: the centrifugal water pump and the positive displacement water pump.
Centrifugal water pump
A centrifugal water pump creates a centrifugal force that helps rotate water while adding pressure energy. There are various types of centrifugal water pumps which include the following:
Horizontal centrifugal water pump
A horizontal centrifugal water pump is a pump that is installed in a horizontal orientation. The pump is suitable for use where the head is adjacent to the prime mover (electric motor or IC engine) on a horizontal plane. A coupling connects the pump shaft to the prime-mover shaft. However, other pumps do not have coupling. The pump is ubiquitous, and thus its spare parts are easily accessible. The pump is easy to repair since the pump parts are easily accessed. Water pump manufacturers recommend the use of this pump in an application where there is limited vertical space.
Figure: Horizontal centrifugal water pump.
Vertical centrifugal water pump
A vertical centrifugal water pump is a pump that is installed in a vertical orientation. Water pump manufacturers develop this pump such that it can draw water from deep wells or deep tanks. These pumps are of various sizes and shapes but have distinctive vertical configurations. The pump is best suited for installation in areas with limited floor space and sufficient headroom. The pump operates by converting kinetic energy created by rotating impellers into pressure energy that helps to transfer water to the needed destination. However, this type of pump becomes a challenge to repair because it is installed deep, making it hard to access pump parts for repair.
Figure: vertical centrifugal water pump.
Single-stage centrifugal water pump
A single-stage centrifugal water pump is a pump that operates with one impeller. It is the most common of all pumps. The pump is either of vertical or horizontal configuration. It is preferred due to its small size and compact design, making it easy to repair. A single-stage centrifugal water pump is cheaper than a pump with more than one impeller. However, it is suitable for pumping water for smaller heads and flow rate relative to the multistage type of pump.
Multistage centrifugal water pump
A multistage centrifugal water pump is either of vertical or horizontal configuration. Water pump manufacturers design this pump to operate with more than one impeller. Each impeller constitutes a water flow stage; hence the number of impellers equals the number of stages. The pump impellers are arranged in series from left to right. Such design allows water to flow through each stage from the inlet to the discharge. At each stage, water pressure increases until the water leaves the final impeller. As such, the water gains more pressure energy, and thus it can move for a higher head relative to the single-stage pump. This pump can also achieve high heads, like 2000m3/hour. However, due to the impellers used, the pump is prone to clogging, and repair and maintenance become hard.
Figure: Vertical and horizontal multistage centrifugal water pumps.
Self-priming centrifugal water pump
A self-priming pump is designed with features that fully support it prime itself. Manufacturers create this pump with a reservoir holding water for priming. The pumps that do not have self-priming capabilities are primed manually. The manual priming process entails adding water to the pump to expel air. If the air is not removed, the pump will not create the required vacuum to force atmospheric pressure to push water into the pump. When it comes to a self-priming pump, it creates a vacuum when the impellers rotate. With the vacuum, a mixture of air and water moves up the pump toward the discharge port. Air has a lower density than water; thus, air floats on the water and is expelled through the discharge. The water then moves down into the pump, where it mixes with any remaining air and moves up the pump, where the air is again expelled. The process keeps on until all the air is expelled. After removing all the air, the pump starts the normal pumping process.
Figure: Self-priming centrifugal water pump.
Positive displacement pumps
Positive displacement pumps are pumps that transfer water using the action of screws, gears, pistons, vanes, screws, or diaphragm. In these pumps, a specific amount of water is enclosed in the compression chamber. After compression, a certain amount of water is discharged. Positive displacement water pumps are also known as constant volume pumps due to their constant flow rate and speed. The following are some of the positive displacement water pumps.
The gear pump uses two gear sets: the driving gear and the driven gear. The driving gear is connected to the prime mover, which, in most cases, is an electric motor. This helps to transmit power from the engine to the gears. The gears rotate in the opposite direction, which helps to create a vacuum in the suction side of the pump. The vacuum forces water into the pump. When the water reaches between the driver and the driven gear, it gets trapped. The trapped moisture moves with the rotating gears and keeps its motion from the inlet to the discharge side. Next, the high-pressure water exits the pump via the discharge port and moves along the pipeline to the required destination.
The screw pump operates similarly to the gear pump. The pump has several screws, the primary being driver and driven screw. Driver and driven screws mesh with each other. When the screws rotate, water is sucked into the pump from the tank through a suction pipe. The screw helps the water to move from the suction to the discharge side.
Applications of water pumps
- These pumps are used in the municipal and domestic water supply.
- Water pumps are also used to supply water for construction applications.
- They are used in the collection of water needed for agriculture and irrigation.
- These pumps are used in dewatering to clear floods.
- These pumps are used in steam power plants to supply the water required for cooling the plant system.
- Water pumps are used in water treatment and cleaning applications.
- They are used in high-pressure washing applications.
- Water pumps are used as booster pumps in the long-distance transportation of water.
- These pumps are used in firefighting applications.
Advantages of centrifugal water pumps
- Centrifugal water pumps are highly available in the market relative to the PD pumps.
- They are cheap.
- These pumps can pump clean and dirty water.
- Centrifugal water pumps are of various types allowing users to purchase a pump of their choice relative to the water demands.
- These pumps can be operated using an IC engine or an electric motor.
- They are versatile in size.
Disadvantages of centrifugal water pumps
- These pumps need to be primed before the normal water pumping.
- They are prone to cavitation.
- These pumps have low suction power.
Troubleshooting centrifugal water pumps
The pump starts, but no water flows
- The pump is not primed. Prime the pump.
- There is no power on the motor. Check the motor power cables are correctly and firmly connected.
- The discharge valve is closed. Open the discharge valve.
- The suction valve is closed. Open the discharge valve.
- The suction pipe is blocked. Open the suction pipe and clear off any blocking materials.
- The motor shaft rotates in the wrong direction. Check the motor shaft direction of rotation matches the arrow indicated on the pump casing.
- The suction lift is too high. Lower the pump or raise the level of water in the tank.
Water flow decreases/low water flow
- Leakage through seals. Replace the pump seals.
- Leakage through the suction line. Repair or replace the suction pipe.
- Strainer or suction valve is clogged. Check the filter or suction valve and clean off materials causing a blockage.
The pump produces a lot of noise/vibration.
- The pump operates outside its duty range. Ensure the pump operates at the range recommended by the water pump manufacturer.
- The impeller is partially clogged. Clean off blocking materials.
- The bearings are worn out. Replace the bearings.
- Defective or worn-out impeller. Replace impeller.
- Misalignment on shaft/coupling. Align shaft/coupling properly.
Troubleshooting positive displacement pumps
Low water flow capacity
- The speed is too low. Increase pump speed to the range recommended by the water pump manufacturer.
- Leakage via valves. Repair or replace the valves accordingly.
- The liner or piston ring is worn out. Replace the liner/ring.
The pump is experiencing excessive wear
- Pump shaft misalignment. Align the shafts properly.
- Bend on the shaft. Straight the shaft.
- There is no lubrication on the bearings. Lubricate the bearings.
- The bearing cover needs to be tight enough. Loosen the cover.
- Misalignment of the shaft. Realign the pump shafts.
Water pumps are designed for use in transporting water. The water could be clean or dirty. However, water pump manufacturers have pumps specifically for clean water and those meant for dirty water. Water pumps are of various types. Centrifugal and positive displacement water pumps are the two main types. For a centrifugal water pump, the impellers rotate at high speed creating a vacuum. The vacuum forces water into the pump. The impellers also help to impart kinetic energy into the water. As the water moves out of the pump, its kinetic energy is converted to pressure energy. The pressure energy is responsible for transporting the water to your location. Some types of centrifugal water pumps include horizontal, vertical, single-stage, multistage, and self-priming pumps, among others.
Positive displacement water pumps transfer water through the action of screws, gears, vanes, pistons, plungers, or diaphragms. PD pumps operate by transferring a specific quantity of water which has earned them the name constant volume water pump since they are capable of constant speed and flow rate. Some PD water pumps include gear pumps, screw pumps, diaphragm pumps, piston pumps, and plunger pumps.