Self-priming Magnetic Pump
Self-priming Magnetic Pump
What is self-priming magnetic pump?
This is a pump designed with self-priming capabilities. It can pump a mixture of liquid and gas since it can vent the suction pipe of air. This pump operates by recirculating fluid in the pump head creating a vacuum. As such, the air is evacuated from the suction line until when liquid gets into the impeller. By having self-priming capabilities, this pump has low efficiency. Self-priming magnetic pump operates by using magnets. As such, the pump does not depend on mechanical coupling to connect the pump and motor but it uses outer and inner magnets. The two magnets are mounted with their poles opposite which creates a magnetic field pattern forcing the motor rotation to rotate the pump impeller. This type of pump is very special in that it can be used in transporting hazardous and corrosive fluids without any leakage unlike pumps that use mechanical seals.
Figure: Self-priming magnetic pump
Components of a self-priming magnetic pump
This component is responsible for providing the power needed to operate the pump. The electric motor converts electrical energy to mechanical energy depicted through shaft speed and torque.
There are two magnets which are drive and driven. The drive magnet is rotated by the motor shaft so that through a magnetic field pattern it can rotate the driven magnets.
The impeller is the component of a self-priming magnetic pump used to impart velocity onto the fluid so that it can move to the delivery pipe.
This is the shaft on which the impeller is mounted. This shaft is supported on bearings to make its rotation smooth.
The casing is the component used to seal off the internal parts of the pump against the atmosphere to prevent fluid leakage and also retain fluid pressure. Self-priming magnetic pump manufacturers produce the casing from strong materials that ensure high strength against fluid pressure and impact damage. The casing also helps to reduce fluid velocity as it increases pressure energy needed to transport the fluid to the required destination.
This component is mounted on the suction end of the pump and its purpose is to filter the liquid to eliminate solids that may get clogged on the impeller.
As the name suggests, this is a valve on the discharge pipe of the pump and it is meant to control fluid flow from the pump. When you need to regulate fluid from the pump to the required destination this is the valve to use.
Figure: Components of a self-priming magnetic pump
How does a self-priming magnetic pump work?
The working of the pump is depended on the power from the motor. To start the pump, the motor is turned on. This makes the motor shaft to rotate the outside magnet. Due to magnetic field pattern the inner magnet also rotates. As such, the impeller rotates. Rotation of the impeller forces fluid to move from the source into the pump due to pressure difference between the pump inside and on the sump.
Due to the impeller rotation, a vacuum is created on the impeller eye. This vacuum moves air from the suction line into the pump. Simultaneously, it creates a ring of liquid inside the casing. This leads to the formation of a gas-tight seal which stops air from returning from the discharge to the suction line. Bubbles of air are trapped in the liquid within the vanes of the impeller and transported to the discharge port. Then the air is expelled while the liquid goes back to the pump housing through gravity. The liquid rises through the suction pipe as it is evacuated. The process continues until all the air in the suction pipe and the pump is replaced by liquid. After that, the normal pumping process starts and the liquid is discharged through the discharge pipe. Self-priming magnetic pump manufacturer design this pump such that when the pump is turned off, the priming chamber retains enough liquid so that the pump can prime itself when it is turned on again.
Figure: Working of a self-priming magnetic pump
Types of self-priming magnetic pumps
Stainless steel self-priming magnetic pump
This is a self-priming magnetic pump that is made of stainless steel material. This pump is very strong owing to the high strength of stainless steel material against high pressure and impact damage. This type of pump is recommended for use at both low and high temperatures since the material can withstand high levels of heat. However, there are limits to which the pump can be exposed to high temperatures. This is because very high temperatures can damage the pump magnets and thus render the pump inoperable or reduce its performance. As such, this pump should only be used at the temperature recommended by the self-priming magnetic pump manufacturer. It is also suitable for use in transporting corrosive products since the stainless steel material can resist corrosion. However, this pump is heavy relative to other pumps made of plastic materials due to the high density associated with steel.
Figure: Stainless steel self-priming magnetic pump.
Plastic-lined self-priming magnetic pump
This is a pump that is made of metallic material like steel but whose interior is coated with a plastic material like Teflon and or polystyrene. This type of pump is very reliable when used to work on corrosive fluids like acids. Plastic materials have good resistance to corrosion relative to metallic ones such as steel. However, this self-priming magnetic pump has the weakness of maximum temperature since plastic materials have low thermal resistance, unlike metallic ones.
Figure: Plastic-lined self-priming magnetic pump.
Single-stage self-priming magnetic pump
This is a pump that is designed to operate with one impeller. The single impeller forms one stage of fluid pressure generation. This pump is small and of lightweight. The pressure energy produced by this pump is smaller compared to the one produced by a pump with more than two impellers. Self-priming magnetic pump manufacturers design this pump to be installed in either vertical or horizontal orientation depending on the available space.
Figure: Single stage self-priming magnetic pump.
Multistage self-priming magnetic pump
This is a pump designed with more than two liquid chambers or stages. These chambers are connected in series. The pump operates by allowing fluid flow from the suction line flow through all the chambers where it leaves at high pressure. The more the stages, the more the discharge pressure. Self-priming magnetic pump manufacturers design the pump such that the flow range remains constant for a certain rpm with the addition of more stages. This pump can be installed in either vertical or horizontal plane.
Figure: Multistage self-priming magnetic pump.
Applications of self-priming magnetic pump
- These pumps are used in an oil refinery for transporting petroleum products.
- They are used in the transportation of chemicals such as acids and alkalis.
- Self-priming magnetic pumps are used in the treatment of water.
- They are used in the transportation of cooling lubricants.
- They are used in food and beverage manufacturing.
- They are used in the transportation of corrosive and hazardous liquids.
- They are used in heat exchanger systems.
Advantages of self-priming magnetic pumps
- These pumps are leakage-proof. The pump uses magnetic coupling that eliminates the possibility of fluid leakage common in pumps with mechanical seals. As such, it eliminates the risk of wasting liquids being transported and or exposing the liquid to people working on the piping system.
- This pump is reliable in its operation as it rarely breakdown if it is being used according to the instructions given by the self-priming magnetic pump manufacturer. This property also helps to reduce maintenance and repair costs.
- It does not have a shaft misalignment problem. This pump is designed with a small air gap between the pump, magnet, and motor. This eliminates physical contact and thus eliminates thermal expansion and misalignment which can cause premature wear and failure.
- Self-priming magnetic pumps help reduce the risk of fines where the pump is used to transport hazardous and corrosive liquid. The manufacturers adhere to strict design regulations about safety and the environment which results to a pump free from leakage ensuring such fluids cannot leak causing damage to the environment and thus fines.
- They can transport liquids of a wide range of viscosity and density.
- Self-priming magnetic pumps are suitable for use in intermittent and frequent pumping operations since the steps involved in priming when starting the pump are eliminated.
- This pump is also able to pump liquid even when it is not submerged in the liquid.
Disadvantages of self-priming magnetic pumps
- These pumps are limited to the level of operating temperature. Very high temperatures can damage the magnets. As such, the pump should only be used at the recommended temperature range.
- Self-priming magnetic pumps have limited power and torque. If the torque exceeds the recommended level of the magnetic coupling strength, the magnets decouple rendering the pump inoperable.
- They are limited to handling solids since they stick to the magnets and thus reduce pump performance.
Troubleshooting self-priming magnetic pumps
Low fluid flow
- Debris in the suction pipe. Clean debris in the suction line, suction valve, and filters.
- Motor rotating in the reverse or it has a low speed. Change the motor rotation if it is spinning in the reverse. If the motor has a low speed check the voltage and frequency as recommended by the self-priming magnetic pump manufacturer.
- Leakage through the suction line. Check the gaskets and flange connections on the suction pipe. If the gasket is worn out replace it. Tighten the bolts to attain torque recommended by the self-priming magnetic pump manufacturer.
- The suction line is not primed. Prime the pump suction line sufficiently.
- High discharge resistance. Clean the discharge pipe of materials causing flow resistance.
High fluid flow rate
- The outlet control valve is wide open. Turn the discharge control valve to reduce fluid flow.
- Low fluid viscosity. Ensure the pump is working on the fluid of the recommended viscosity.
- High motor speed. Check the motor voltage and frequency are as recommended by the self-priming magnetic pump manufacturer.
No fluid flow through the pump
- Damaged pump. Check the motor windings and phases. If necessary replace the motor.
- Blockage within the pump. Open the pump and remove any material causing blockage.
- The Inlet valve is closed. Open the inlet valve.
- The discharge valve is closed. Open the discharge valve.
- No liquid in the tank. Ensure the tank has enough liquid.
- The Head is too high. Ensure the manometric head matches the pump design pressure.
Excessive noise and vibration
- Worn out bearings. Replace the bearings.
- Clogged impeller. Clean off foreign materials on the impeller.
- Too high motor speed. Check the motor frequency and voltage are as recommended.
The self-priming magnetic pump is designed to automatically prime itself. The air bubbles contained in the liquid are separated and they escape through the discharge nozzle while the fluid goes back to the pump housing. This ensures the suction line is evacuated continuously. When the pump is stopped, the pump stores the fluid so that when the pump is started again it can prime itself. Self-priming magnetic pump manufacturers employ magnets to transmit power from the motor to the pump instead of using shaft coupling. The magnets are two with one outside and the other inside the pump. They are arranged with their poles opposite to create a magnetic field pattern. As such, rotation of the motor shaft forces the outside magnet to rotate, and thus the inner magnet also spins. Rotation of the inner magnet forces the impeller to spin and thus the pump starts working.
Self-priming magnetic pump manufacturers produce different types of pumps such as single-stage pumps, multistage pumps, plastic-lined pumps, and stainless steel pumps among others. Applications of this pump include chemicals, petrochemicals, lubricating oil, foods and beverages, cryogenics, crystallizing fluids, and water treatment among others. The advantages of these pumps are durability, leakage proof, reduced fines, no misalignment, low maintenance, reliability, and ability to handle entrained gases.