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How Do Centrifugal Pumps Work?

Sep. 03, 2022

Centrifugal is actually the performance of the inertia of the object, such as the water droplets on the umbrella, when the umbrella slowly rotates, the water droplets will follow the umbrella rotation, this is because the friction between the umbrella and the water droplets as the centripetal force to the water droplets make. But if the umbrella rotates faster, the friction force is not enough to make the water droplet in circular motion, then the water droplet will be separated from the umbrella to the outer edge of the movement, just like a rope pulling a stone to do circular motion, if the speed is too fast, the rope will break, the stone will fly out. This is the so-called centrifugal.


Main working principle of Centrifugal Pumps

(1) The impeller is driven by the pump shaft rotation, the fluid located between the blades to do work, the fluid by the centrifugal effect, from the center of the impeller is thrown to the periphery. When the fluid reaches the outer circumference of the impeller, the flow rate is very high.


(2) The pump casing collects the liquid thrown from each vane, these liquids flow in the casing in the direction of the worm-shaped channel gradually expanding, so that the kinetic energy of the fluid into static pressure energy, reduce energy loss. So the role of the pump shell is not only in the collection of liquid, it is an energy conversion device.


Vertical Centrifugal Ceramic (SIC) Sump Pump

(3) Liquid suction principle: rely on the impeller high-speed rotation, forcing the impeller center of the liquid to be thrown away at a very high speed, thus forming a low pressure in the center of the impeller, the liquid in the low slot is therefore constantly sucked up.


Gas-bound phenomenon: If the centrifugal pump is filled with gas in the casing before starting, the gas in the center of the impeller is thrown after starting cannot form a large enough vacuum in the place, so that the liquid in the tank can not be sucked on. This phenomenon is called gas binding.


In order to prevent the occurrence of gas binding phenomenon, centrifugal pump before starting to fill the space inside the pump casing with external liquid. This step is called pump filling. In order to prevent the liquid filled into the pump casing from flowing into the low level tank due to gravity, a check valve (bottom valve) is installed at the entrance of the pump suction line; if the pump position is lower than the liquid level in the tank, there is no need to fill the pump when starting.


(4) The impeller is equipped with a guide wheel at the outer circumference of the impeller, so that the liquid in the pump has high efficiency in energy conversion. The guide wheel is a fixed ring with vanes located at the periphery of the impeller. The bending direction of these blades is opposite to the bending direction of the impeller blades, and its bending angle is exactly the same as the direction of liquid flow from the impeller, guiding the liquid in the pump casing channel to change direction smoothly, so that the energy loss is minimal, and the efficiency of the conversion of dynamic pressure energy into static pressure energy is high.


(5) The balance hole on the rear cover plate eliminates axial thrust. Leave the impeller around the liquid pressure has been higher, part of it will seep to the back side of the impeller back cover plate, while the front side of the impeller liquid inlet for low pressure, thus creating the impeller to the pump inlet side of the axial thrust. This is likely to cause wear at the contact between the impeller and the pump casing, and in serious cases, vibration will be generated. Balance hole so that part of the high pressure liquid leakage to the low pressure area, reduce the pressure difference between the front and rear of the impeller. But this will also cause a reduction in pump efficiency.


(6) Shaft sealing device to ensure normal and efficient operation of centrifugal pumps. Centrifugal pump in the work of the pump shaft rotation and shell does not move, the ring gap between if not sealed or sealed bad, the outside air will penetrate into the impeller center of the low-pressure area, so that the pump flow, efficiency decline. In severe cases, the flow is zero - air binding. Usually, mechanical seal or packing seal can be used to achieve the seal between the shaft and the shell.



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