What is the peripheral pump?
This pump is also known as a regenerative pump. It is designed with impellers that rotate in a concentric casing. This type of pump lies between positive displacement pumps and centrifugal pumps even though it operates similar to centrifugal pump. Peripheral pump manufacturers design this pump such that the liquid moves along the inlet to the outlet along the circumference of the casing while the pressure increases. Owing to the large increase in pressure energy, these pumps are relatively small in size. They are mostly close-coupled pumps. This pump can be single-stage (one impeller) or multistage (more than one impeller). Peripheral pump is capable of transporting fluids with a relatively high content of gas since extreme vapor bubble formation does not cause a cut-off to fluid flow or cause a major impact on the pump operating smoothly.
The efficiencies of these pumps are low relative to radial pumps. Peripheral pump manufacturers recommend this pump for use in uncontaminated fluids such as boiler feed pumps for relatively small boilers, pressure boosters, chemical industries, and car washes among others in which the fluid needs to be pumped at high pressure.
Figure: Peripheral Pump
Components of a peripheral pump
The motor is the source of power for a peripheral pump. This motor is powered by electricity in which it operates by converting the electrical energy into mechanical power. The electrical energy is supplied by the mains electricity line. The mechanical power is provided in terms of torque and speed depicted on the motor shaft.
This is the part of the pump that rotates at high speed to create a vacuum in the pump. This vacuum is meant to force fluid from its source into the pump. Peripheral pump manufacturers design the impeller with radial vanes. Such vanes are used to rotate the fluid as it enters the pump.
This is the pump housing meant to seal off the atmosphere to the pump interior and prevent fluid leakage. The casing is designed to allow fluid to rotate between it and the impeller as the fluid kinetic energy is converted to pressure energy. This high-pressure energy is used to move the fluid to the required destination. Peripheral pump manufacturers produce the casing from high strength materials like stainless steel or cast iron to ensure it can withstand high fluid pressure.
Suction pipe and valve
The suction pipe is used to connect the pump inlet port to the source of the liquid like a tank. This is the pipe that is used to convey the liquid from its source into the pump when the impeller starts rotating. The suction valve is used to regulate the amount of fluid that flows into the pump. Peripheral pump manufacturers also design this valve with a strainer to help filter out any foreign materials from getting into the pump and causing a blockage.
Discharge pipe and valve
The discharge pipe connects the pump to the pipe network. The valve is used to regulate the fluid flowing from the pump to the pipeline.
Figure: Components of a peripheral pump
How does a peripheral pump work?
The power to operate this pump is provided by the electric motor. When the pump is turned on, the motor shaft rotates at a very high speed. This rotary speed is transmitted to the impeller via the shaft. As such, the impellers start rotating at the same high speed creating a vacuum in the pump. This vacuum helps to suck fluid from its source into the pump. Peripheral pump manufacturers design the impeller with a large number of small radial blades that are mounted along the peripheral area.
Due to the rotating impeller, centrifugal force is created inside the pump. This force inside the impeller creates a circulatory flow between itself and the casing. The impeller and the fluid peripheral speed are the same, while the fluid within the casing has a significantly lower speed. As such, the liquid moves from the casing to the impeller in a spiral-like path. This flow path is repeated several times along the circumference. The more frequently these vortexes are formed, the higher the energy, and thus, the more fluid pressure. When the flow is reduced, the number of spirals reduces, and thus the transfer energy and the absorbed power are more in the case of partial loads.
Figure: Working of a peripheral pump
Types of peripheral pumps
Self-priming peripheral pump
This is a pump designed with the capability to prime itself every time it starts working. The priming process is meant to remove entrained air in the suction pipe. This air must be removed before the pump starts transporting fluid to the pipeline otherwise it will damage the pump or cause low fluid flow. In its priming state, this pump acts like a liquid ring pump. It operates by producing a vacuum in the pump. This vacuum helps to move air into the pump from the suction pipe. It also helps to create a cylindrical ring of the fluid on the interior of the pump housing. Such a design helps to create a gas-tight seal that stops air from returning from the discharge end to the suction line. Bubbles of air get trapped in the liquid on the impeller vanes and then they are moved to the discharge port. The air is then expelled and the liquid goes back to the reservoir in the pump casing under gravity. The liquid goes up the suction pipe as it is being evacuated.
The process goes on until all the air in the suction pipe and the pump is replaced by the liquid. Once all the air is removed, the normal pump operation starts. Peripheral pump manufacturers design this pump such that when the pump is turned off, there remains enough liquid in the pump so that the pump can prime itself in the next pumping process.
Figure: Self-priming peripheral pump.
Magnetic drive peripheral pump
This is a pump that uses magnetic technology to drive the impeller. Peripheral pump manufacturers design this pump with two magnets that are the outer (drive) and inner (driven) magnets. The outer magnet is connected to the motor while the inner magnet is mounted in the pump. When the motor shaft rotates, it forces the outer magnet to rotate at the same speed. Due to the magnetic field pattern, the inner magnet also rotates at the same speed as the outer magnet. Since the inner magnet is connected to the impeller shaft, it forces the impeller to spin at the same speed. This creates a vacuum in the pump which then draws the liquid for pumping. This type of pump is very good for use in applications that involve hazardous fluids like acids and other chemicals. This is because the pump does not use mechanical seals which can leak such liquids and thus it helps to reduce chances of environmental damage or legal action. However, it comes at very high cost relative to other pumps.
Figure: Magnetic drive peripheral pump.
Single-stage peripheral pump
This is a pump designed with one impeller. This is one of the most frequently used peripheral pumps. It is preferred due to its simple design, low cost, and ease to repair. However, this pump has low-pressure energy relative to other pumps with more than one impeller.
Multistage peripheral pump
This is a pump designed with more than one impeller. It is recommended for use in applications that need large-pressure energy. The more the number of impellers, the higher the pressure energy produced. This pump is expensive relative to the single stage and it is also large in size.
Plastic-lined peripheral pumps
This is a pump whose interior is lined with a plastic material such as Teflon and or PVC. This pump is best suitable for handling corrosive liquids like acids and salty water. The main use of the plastic coat is to help prevent the wear of metallic components by corrosive products. However, the use of this pump is limited to only low temperatures since its use at high heat levels would distort the plastic lining.
Applications of peripheral pumps
- These pumps are used in sprinkler irrigation.
- They are used in the commercial and domestic water supply.
- Peripheral pumps are used as pressure boosters.
- They are used in chemical applications to transport chemicals like acids.
- They are used in boiler feed systems.
Advantages of peripheral pumps
- They are of simple and compact design.
- They are easy to install, repair, and maintain.
- They are of various sizes suiting their use in different areas.
- Peripheral pumps can produce very high pressure at a low fluid flow rate.
- They are capable of handling entrained gas without cavitation risks. Also, peripheral pump manufacturers produce self-priming pump types making them suitable to handle air ingress.
- They have a low net positive suction head.
Disadvantages of peripheral pumps
- They cannot produce fluid flow quickly.
- They produce a low fluid flow rate relative to centrifugal pumps.
- The efficiencies of this pump are lower relative to other pumps.
- They are not suitable for handling contaminated liquids.
Troubleshooting peripheral pumps
No liquid is delivered
- The electric motor is not working. Check the motor windings and correct if there is any fault. Replace the motor if necessary.
- Shaft misalignment. Check shaft and coupling alignment. Align any misalignment.
- Solid particles clogged the pump. Open the pump and remove any material causing fluid blockage.
- Seizure on bearings. Replace the bearings with ones recommended by the peripheral pump manufacturer.
- The suction valve closed. Open the suction valve.
- The discharge valve closed. Open the discharge valve.
- Low liquid level in the tank. Increase the liquid level.
- Blocked strainer. Clean off the strainer.
- Wrong direction of rotation of the motor. Change the direction of rotation.
Excessive power consumption
- Clogged particles in the discharge pipe. Disconnect the discharge pipe and remove the dirt and refit.
- Misalignment of shafts or coupling. Check shaft or coupling misalignment and align as necessary.
- Fluid temperature, viscosity, or pressure is outside the recommended range. Ensure the pump is used at the specifications given by the peripheral pump manufacturer.
- Worn out parts. Replace worn-out components such as bearings, shafts, and mechanical seals.
- Seals are worn out or not well installed. If seals are worn out, replace them. Also, check if they are well-fitted.
- Damaged O-rings. Replace O-rings.
- Loose fasteners. Tighten the fasters to attain the torque recommended by the peripheral pump manufacturer.
- Excess static pressure. Ensure the system pressure is as recommended.
Low fluid flow/ output pressure
- The motor is faulty. Check the motor windings and phases.
- Foreign materials in the suction line. Remove the foreign materials.
- Incorrect motor speed. Check the motor frequency and voltage are as recommended by the peripheral pump manufacturer.
- Worn out bearings. Replace the bearings.
- Foreign materials in the pump. Remove the materials.
Loose connection. Tighten the connecting bolts and nuts.
Peripheral pumps are pumps designed with impellers that have several blades on them. The fluid flows in this pump repeatedly between the pump casing and the impeller forming a spiral path. This pump is powered by an electric motor which causes the impeller to spin at high speed. As such, the impeller rotation causes a centrifugal force in the pump creating a circulatory fluid flow between the impeller and casing. The fluid peripheral speed and the impeller are the same but the fluid in the casing has a lower speed. This makes the fluid move from the casing to the impeller forming a spiral-like path.
Peripheral pump manufacturers produce various types of pumps such as self-priming pumps, magnetic drive pumps, single-stage pumps, multistage pumps, and plastic pumps among others. Applications of this pump are water supply, pressure boosting, and boiler feeds water systems among others. The advantages of this pump are high pressure, versatility, easy installation and repair, and can handle trained air without cavitation.