Magnetically of Centrifugal

Coupled pumps

Magnetically coupled or magnetic drive pumps differ from traditional pumping methods because the motor is magnetically coupled to the pump rather than through a direct mechanical shaft.The pump works by driving magnets that "drive" the pump rotor, which is magnetically coupled to a main shaft driven by an electric motor.They are often used where leakage of the pumped fluid presents a significant risk (for example, corrosive fluids in the chemical or nuclear industries, or electric shock garden fountains).They do not have a direct connection between the motor shaft and the impeller, so no stuffing box or gland is required.There is no risk of leakage unless the casing is ruptured. Since the pump shaft is not supported by bearings outside the pump casing, support within the pump is provided by bushings.Magnetic drive pumps can range in pump size from a few watts to the massive 1 megawatt.

Priming 

The process of filling the pump with liquid is called priming.All centrifugal pumps require liquid in a liquid housing to start.If the pump casing is filled with steam or gas, the pump impeller becomes trapped by the gas and cannot pump.To ensure that centrifugal pumps remain primed and are not gas-bound, most centrifugal pumps are located the water level of the pump suction source.The same effect can be achieved by supplying liquid to the pump suction under pressure provided by another pump placed in the suction line.

Self-priming centrifugal pump

Ordinary centrifugal pumps cannot, under normal conditions, remove air from the inlet line leading to a liquid level whose earth gauge height is below the pump's liquid level.Self-priming pumps must be able to evacuate air from the pump suction line without any external auxiliary equipment.Centrifugal pumps with an internal suction stage, such as water jet pumps or side channel pumps, are also classified as self-priming pumps.The self-priming centrifugal pump was invented in 1935.One of the first companies to bring a self-priming centrifugal pump to the market was the American Marsh.Centrifugal pumps that are not designed with internal or external self-priming stages can only begin pumping fluid after the pump is initially primed with fluid.Their impellers are stronger but slower and are designed to move liquids that are much denser than air, so they cannot operate when air is present.Additionally, a suction side swing check valve or discharge valve must be installed to prevent any siphoning action and to ensure that fluid remains in the housing when the pump is stopped.In self-priming centrifugal pumps with a separation chamber, the pumped fluid and entrained air bubbles are pumped into the separation chamber by impeller action.

Air escapes through the pump discharge nozzle while the fluid falls back and is entrained again by the impeller.The suction line is thus continuously evacuated.The design required for this self-priming function has an adverse effect on pump efficiency.Also, the size of the separation chamber is relatively large.For these reasons, this solution is only suitable for small pumps, such as garden pumps. The more commonly used types of self-priming pumps are side channel pumps and water ring pumps.Another type of self-priming pump is the centrifugal pump, which has two housing chambers and an open impeller.This design is not only used for its self-priming capability, but also for its degassing effect when pumping two-phase mixtures (air/gas and liquid) for short periods of time in process engineering or when handling contaminated fluids, e.g. when draining water from construction pits.This pump operates without a foot valve and has no evacuation device on the suction side.The pump must be primed with the fluid to be treated before commissioning. Pump the two-phase mixture until the suction line is evacuated and the liquid level is pushed into the forward suction chamber by atmospheric pressure.During normal pumping operation, the pump works in the same way as a normal centrifugal pump.