How centrifugation works

Centrifugation is actually a manifestation of the inertia of an object, such as water droplets on an umbrella. When the umbrella rotates slowly, the water droplets will follow the umbrella. This is because of the relationship between the umbrella and the water droplets. Friction acts as a centripetal force on the water droplet. But if the umbrella rotates faster and the friction is not enough to make the water droplets move in a circular motion, then the water droplets will move away from the umbrella and toward the outer edge, just like pulling a stone with a rope to make a circular motion. If the speed is too fast, the rope will If it is disconnected, the stones will fly out. This is the so-called centrifugal force.

The main working principle of a centrifugal pump

(1) The impeller is driven by the pump shaft to rotate, doing work on the fluid between the blades. The fluid is affected by the centrifugal force and is thrown from the center of the impeller. Periphery. When the fluid reaches the outer periphery of the impeller, the flow rate is very high.

(2) The pump casing collects the liquid thrown from between the blades. The liquid flows in the casing along the gradually expanding direction of the volute-shaped channel, converting the kinetic energy of the fluid into static pressure energy. Reduce energy loss. Therefore, the role of the pump housing is not only to collect liquid, but also an energy conversion device.

(3) 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 very high speed, thus forming a low pressure in the center of the impeller, and the liquid in the low tank is continuously being pushed away. Suction up.

Gas Binding Phenomenon

Gas Binding Phenomenon: If the centrifugal pump casing is filled with gas before starting, the gas in the center of the impeller will not form a large enough volume after starting. The degree of vacuum is so that the liquid in the tank cannot be sucked up. This phenomenon is called air binding.

In order to prevent the occurrence of air binding, the space inside the pump casing must be filled with external liquid before starting the centrifugal pump. 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 pipe; if the position of the pump is lower than the liquid level in the tank, there is no need to fill the tank when starting. pump.

(4) A guide wheel is installed around the impeller to make the energy conversion efficiency of the liquid in the pump high. The stator is a fixed, bladed ring located around the periphery of the impeller. The bending direction of these blades is opposite to the bending direction of the impeller blades. The bending angle is just in line with the direction of the liquid flowing out from the impeller, guiding the liquid to change direction smoothly in the pump casing channel, minimizing energy loss and converting dynamic pressure energy into static energy. The efficiency of pressure energy is high.

(5) The balance hole on the rear cover eliminates axial thrust. The pressure of the liquid leaving the periphery of the impeller is already high, and part of it will seep into the rear side of the impeller rear cover. The liquid inlet on the front side of the impeller is at low pressure, thus generating an axial thrust that pushes the impeller to the pump inlet side. This can easily cause wear at the contact point between the impeller and the pump casing, and may even cause vibration in severe cases. The balance hole allows part of the high-pressure liquid to leak into the low-pressure area, reducing the pressure difference before and after the impeller. However, this will also cause a reduction in pump efficiency.

(6) The shaft seal device ensures the normal and efficient operation of the centrifugal pump. When a centrifugal pump is working, the pump shaft rotates but the shell does not move. If the annular gap is not sealed or is not well sealed, the outside air will penetrate into the low-pressure area in the center of the impeller, causing the pump flow and efficiency to decrease. In severe cases, the flow rate is zero - air binding. Usually, mechanical seals or packing seals can be used to achieve sealing between the shaft and the housing.

Introduction to the working principle of the centrifugal pump

Introduction to the working principle of the centrifugal pump

Picture of the centrifugal pump

The main flow-passing parts of the centrifugal pump There are suction chamber, impeller and pressure water chamber. The water suction chamber is located in front of the water inlet of the impeller and plays the role of guiding the liquid to the impeller; the pressure water chamber mainly has three forms: spiral pressure water chamber (volute type), guide vane and space guide vane; the impeller is the most important part of the pump. The important working component is the heart of the flow-passing component. The impeller consists of a cover plate and a middle blade.

Before the centrifugal pump works, first fill the pump with liquid, and then start the centrifugal pump. The impeller rotates rapidly. The blades of the impeller drive the liquid to rotate. When the liquid rotates, it relies on inertia to flow to the outer edge of the impeller. At the same time, the impeller moves from The suction chamber sucks in liquid. During this process, the liquid in the impeller flows around the blades. During the flow movement, the liquid exerts a lift force on the blades. In turn, the blades act on the liquid with a force equal to this lift force and in the opposite direction. , this force does work on the liquid, causing the liquid to gain energy and flow out of the impeller. At this time, the kinetic energy and pressure energy of the liquid increase.

Centrifugal pumps rely on the action of the rotating impeller on the liquid to transfer the mechanical energy of the prime mover to the liquid. Due to the action of the centrifugal pump, when the liquid flows from the impeller inlet to the outlet, its velocity energy and pressure energy are increased. When the liquid discharged by the impeller passes through the pressure chamber, most of the velocity energy is converted into pressure energy, and then transported along the discharge pipeline. At this time, a vacuum or low pressure is formed at the impeller inlet due to the discharge of liquid. The liquid in the suction pool is forced into the impeller inlet under the action of the liquid surface pressure (atmospheric pressure). As a result, the rotating impeller rotates continuously. Aspirate and expel fluids.

Basic structure of centrifugal pump

IRG centrifugal pump

The basic structure of centrifugal pump is composed of six parts, namely: impeller, pump body, pump shaft , bearings, sealing rings, stuffing boxes.

1. The impeller is the core part of the centrifugal pump. It has high speed and large output force, and the blades on the impeller play a major role. The impeller must pass a static balance test before assembly. The inner and outer surfaces of the impeller must be smooth to reduce friction losses in the water flow.

2. The pump body is also called the pump casing, which is the main body of the water pump. It plays a supporting and fixing role and is connected to the bracket where the bearing is installed.

3. The function of the pump shaft is to connect the motor with the coupling and transmit the torque of the motor to the impeller, so it is the main component for transmitting mechanical energy.

4. The bearing is a component that is sleeved on the pump shaft to support the pump shaft. There are two types of rolling bearings and sliding bearings. Rolling bearings use butter as a lubricant. The oil should be refueled appropriately, generally 2/3 to 3/4. Too much will cause heat, and too little will cause noise and heat!

The sliding bearing uses transparent oil as lubricant, add oil to the oil level line. Too much oil will seep out along the pump shaft and drift away, and too little bearings will overheat and burn out, causing accidents! During the operation of the water pump, the temperature of the bearings reaches a maximum of 85°C and generally runs around 60°C. If it is too high, find the cause (whether there are impurities, whether the oil is black, whether water has entered) and deal with it in time!

5. The sealing ring is also called the leakage reduction ring. If the gap between the impeller inlet and the pump casing is too large, the water in the high-pressure area in the pump will flow to the low-pressure area through this gap, affecting the water output of the pump and reducing the efficiency! If the gap is too small, it will cause friction between the impeller and the pump casing and cause wear. In order to increase the backflow resistance, reduce internal leakage, and extend the service life of the impeller and pump casing, a sealing ring is installed at the joint between the inner edge of the pump casing and the outer edge of the impeller. The sealing gap is preferably maintained between 0.25 and 1.10mm.

6. The stuffing box is mainly composed of packing, water seal ring, stuffing barrel, packing gland and water seal tube. The main function of the stuffing box is to close the gap between the pump casing and the pump shaft, so as to prevent the water in the pump from flowing outside and not allowing outside air to enter the pump. Always maintain a vacuum inside the water pump! When the friction between the pump shaft and the packing generates heat, the water seal tube must be filled with water into the water seal ring to cool the packing! Keep the water pump running properly. Therefore, special attention should be paid to the inspection of the stuffing box during the inspection of the water pump operation! The packing must be replaced after about 600 hours of operation.

7. Axial force balance device During the operation of the centrifugal pump, since the liquid enters the impeller under low pressure and flows out under high pressure, the pressure on both sides of the impeller is unequal, resulting in a force pointing to the inlet. The axial thrust in the direction will cause the rotor to move axially, causing wear and vibration. Therefore, an axial thrust bearing should be installed to balance the axial force.