Centrifugal pump centrifugal principle
Centrifugation is actually a manifestation of the inertia of objects, such as water drops on an umbrella. When the umbrella rotates slowly, the water drops follow the umbrella. This is because the friction between the umbrella and the water drops acts as a centripetal force for the water drops. But if the umbrella rotates faster, this friction is not enough to make the water droplets move in a circular motion, then the water droplets will move away from the umbrella to the outer edge, just like a rope pulling a rock in a circular motion, if the speed is too fast, the rope will move When disconnected, the rocks will fly out. This is called centrifugation.
The main working principle of centrifugal pump
(1) The impeller is driven to rotate by the pump shaft and does work on the fluid located between the blades. The fluid is thrown from the center of the impeller to the periphery under the action of centrifugal force. When the fluid reaches the outer circumference of the impeller, the flow rate is very high.
(2) The pump casing collects the liquid ejected from between the blades. These liquids flow in the casing along the direction of the volute-shaped passage gradually expanding, so that the kinetic energy of the fluid is converted into static pressure energy and energy loss is reduced. So the role of the pump casing is not only to collect liquid, it is also an energy conversion device.
(3) The principle of liquid suction: relying on the high-speed rotation of the impeller, the liquid in the center of the impeller is forced to be thrown away at a high speed, thereby forming a low pressure in the center of the impeller, and the liquid in the low tank is continuously sucked up.
Air-binding phenomenon: If the casing of the centrifugal pump is filled with gas before starting, when the gas in the center of the impeller is thrown after starting, a sufficient vacuum cannot be formed there, so that the liquid in the tank cannot be sucked up. This phenomenon is called gas binding.
In order to prevent the occurrence of air-binding phenomenon, the space in the pump casing should be filled with external liquid before the centrifugal pump is started. This step is called priming the pump. In order to prevent the liquid poured into the pump casing from flowing into the low tank due to gravity, a check valve (bottom valve) is installed at the inlet of the pump suction pipeline; if the pump position is lower than the liquid level in the tank, no filling is required when starting Pump.
(4) A guide wheel is installed on the outer circumference of the impeller to make the liquid energy conversion efficiency in the pump high. The guide wheel is a fixed bladed ring located on the outer periphery of the impeller. The bending direction of the blades is opposite to the bending direction of the impeller blades, and the bending angle is just in line with the direction of the liquid flowing out of the impeller, guiding the liquid to change direction smoothly in the pump casing channel, minimizing energy loss, and converting dynamic pressure energy into High static pressure energy efficiency.
(5) The balance hole on the rear cover eliminates the axial thrust. The pressure of the liquid leaving the periphery of the impeller is already high, and some of it will seep to the back side of the rear cover of the impeller, and the liquid inlet on the front side of the impeller is low pressure, thus generating an axial thrust that pushes the impeller to the pump inlet side. This is easy to cause the wear of the contact between the impeller and the pump casing, and vibration will occur in severe cases. The balance hole makes part of the high-pressure liquid leak to the low-pressure area, reducing the pressure difference between the front and rear of the impeller. But this will also reduce the pump efficiency.
(6) The shaft sealing device ensures the normal and efficient operation of the centrifugal pump. The centrifugal pump is working when the pump shaft rotates but the shell does not move. If the annular gap in between is not sealed or the seal is not good, the outside air will penetrate into the low pressure area in the center of the impeller, which will reduce the flow and efficiency of the pump. In severe cases, the flow is zero-air binding. Generally, mechanical seals or packing seals can be used to achieve the seal between the shaft and the shell.
