Self-priming centrifugal pump impeller and other components

Self-priming centrifugal pump impeller and other components The impeller of the self-priming centrifugal pump is a key component of the self-priming centrifugal pump.

(1) According to its mechanical structure can be divided into closed, semi-closed and open three. Closed impellers are suitable for conveying cleaning liquids; semi-closed and open impellers are suitable for conveying suspensions containing solid particles, and the efficiency of such pumps is low. When the closed and semi-closed impeller is in operation, a part of the high pressure liquid leaving the impeller may leak into the cavity between the impeller and the pump casing. Because the pressure at the liquid suction inlet at the front side of the impeller is low, the liquid acts on the impeller before and after When the pressure on the side is not equal, there is an axial thrust toward the inlet side of the impeller. This force pushes the impeller to move toward the suction inlet side, causing friction between the impeller and the pump casing, causing serious vibration of the pump and damaging the normal operation of the pump. Drilling several small holes in the rear cover of the impeller reduces the pressure difference between the two sides of the impeller, thereby reducing the adverse effects of axial thrust, but it also reduces the efficiency of the pump. These holes are called balance holes.

(2) The impeller can be divided into single suction type and double suction type according to different suction method. The single suction type impeller has a simple structure and the liquid can only be sucked from one side. The double-suction impeller can simultaneously draw in liquid from both sides of the impeller symmetrically. It not only has a large liquid-absorption capacity, but also basically eliminates axial thrust.

(3) According to the geometry of the blade on the impeller, the blade can be divided into three types: backbend, radial and forward bend. Because the backbend blade is conducive to the conversion of liquid kinetic energy to static pressure energy, it is widely used.

2. The guide wheel of the self-priming centrifugal pump is designed to reduce the energy loss caused by the impact when the liquid leaving the impeller directly enters the pump casing. A stationary guide vane is sometimes provided between the impeller and the pump casing. The vanes in the guide wheel gradually turn the liquid entering the pump casing and the flow passage continuously expands, so that part of the kinetic energy is effectively converted into static pressure energy. Multistage centrifugal pumps are usually equipped with guide wheels. The snail-shaped pump casing, the back-bending blades on the impeller and the guide pulley all improve the conversion rate from kinetic energy to static pressure energy, and they can all be considered as turning devices.

3. Shaft sealing device Because the pump shaft rotates, the pump housing is fixed, and there must be a certain gap between the shaft and the pump housing. In order to avoid leakage of high-pressure liquid in the pump along the gap, or to prevent outside air from entering the pump from the opposite direction, a shaft seal must be installed. Centrifugal pump shaft seals have a stuffing box and mechanical (face) seals. The stuffing box is made by sealing the pump shaft through the ring gap of the pump casing and filling soft packing (such as oil-impregnated or graphite-coated asbestos rope, etc.). The mechanical seal consists of a moving ring mounted on the rotating shaft and a stationary ring fixed on the pump housing. The ends of the two rings are rotated against each other by a spring force and play a sealing role. Mechanical seals are suitable for sealing high occasions, such as conveying acids, alkalis, flammable, explosive and toxic liquids. When the centrifugal pump is started, the pump shaft drives the impeller together to perform a high-speed rotary motion, forcing the liquid to be pre-filled to rotate between the blades. Under the action of the inertial centrifugal force, the liquid moves radially from the center of the impeller to the periphery. The liquid gains energy during the movement through the impeller, the static pressure increases, and the flow rate increases. When the liquid leaves the impeller and enters the centrifugal pump casing, it decelerates due to the gradual enlargement of the flow passage in the casing, and part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipeline in a tangential direction. Therefore, the scroll casing is not only a component that collects the liquid that flows from the impeller, but also a turning device. When the liquid is thrown from the center of the impeller to the periphery, the center of the impeller forms a low-pressure zone. Under the action of the total potential energy difference between the liquid level of the storage tank and the impeller, the liquid is sucked into the center of the impeller. With the continuous operation of the impeller, the liquid is continuously sucked in and discharged. The mechanical energy obtained by the liquid in the self-priming centrifugal pump finally manifests itself as an increase in static pressure energy. The function of the impeller is to directly transfer the mechanical energy of the prime mover to the liquid to increase the static pressure energy and kinetic energy of the liquid (mainly increase the static pressure energy).

1. Impeller The role of the impeller is to transfer the mechanical energy of the prime mover directly to the liquid to increase the hydrostatic energy and kinetic energy of the liquid (mainly increasing static pressure energy). There are three kinds of impeller: open, semi-closed and closed. The open impeller has no cover plate on both sides of the blade, so it is simple to manufacture and easy to clean. It is suitable for conveying materials containing a large amount of suspended solids. The efficiency is low and the liquid pressure is not high; the semi-closed impeller has no cover on the inlet side. The plate, on the other side, has a cover plate, suitable for conveying materials that are easy to precipitate or contain particles, and has low efficiency; the closed impeller has front and rear cover plates on both sides of the blade, which is high in efficiency and is suitable for conveying without impurities Cleaning liquid.

The general centrifugal pump impeller is mostly this type.

2. The function of the pump casing is to confine the impeller in a certain space so that the liquid can be sucked in and pressed out by the action of the impeller. Centrifugal pump casing made of more volute shape, it is also known as volute. As the cross-sectional area of ​​the flow channel gradually expands, the high-velocity liquid thrown from the impeller gradually reduces the flow velocity, so that part of the kinetic energy is effectively converted into static pressure energy. The pump casing not only collects the liquid thrown by the impeller, but is also an energy conversion device.

The concept of centrifugation is actually an indication of the inertia of an object. For example, when an umbrella is slowly rotating, the water droplets follow the umbrella because the friction between the umbrella and the water droplets acts as a centripetal force for the water droplets. However, if the umbrella rotates, To speed up, this friction is not sufficient to make the water droplets in a circular motion, then the water droplets will move out of the outer edge of the umbrella. It is like pulling a stone with a rope to make a circular motion. If the speed is too fast, the rope will be disconnected. The block will fly out. This is called centrifugation. Centrifugal pumps are designed based on this principle. High-speed rotating impeller blades drive the water to rotate, throwing water out to achieve the purpose of transportation. There are many kinds of centrifugal pumps. From the use can be divided into civilian and industrial pumps, from the transmission medium Can be divided into clean water pump, impurity pump, anti-corrosion pump. Centrifugal pump basic structure The basic structure of centrifugal pump is composed of six parts, namely: impeller, pump body, pump shaft, bearing, seal ring, stuffing box.

1. The impeller is the core part of the centrifugal pump. It has a high rotational speed and high output force. The blades on the impeller also play a major role. The impeller passes the static balance test before assembly. The inner and outer surfaces on the impeller are required to be smooth in order to reduce the friction loss of the water flow.

2. The pump body is also called the pump housing and it is the main body of the pump. It plays a supporting and fixing role, and is connected with the bracket that mounts the bearing.

3, the role of the pump shaft is to connect the shaft and the motor, the motor torque transmission to the impeller, so it is the main component of the transmission of mechanical energy.

4. The bearing is a member that is sleeved on the pump shaft to support the pump shaft. There are two kinds of rolling bearings and sliding bearings. The use of butter as a lubricant for rolling bearings should be appropriate. Generally, 2/3 to 3/4 of the volume will be too hot, too little noise and heat! The sliding bearing centrifugal pump structure uses transparent oil as a lubricant and is refueled to the oil level line. Too much oil must seep out along the pump shaft and drift*. Too few bearings must be overheated and burned to cause an accident! The temperature of the bearing during the operation of the pump is up to 85 degrees. Normally the temperature is about 60 degrees. If it is high, the cause must be found (whether there is any impurity, whether the oil is black, whether it is in water) and it is handled in time!

5, the sealing ring, also known as leakage reduction ring. The gap between the impeller inlet and the pump casing is too large. As a result, the water in the high-pressure area of ​​the pump flows to the low-pressure area through this gap, affecting the pump output, and the efficiency is reduced! If the clearance is too small, it will cause friction between the impeller and the pump casing. In order to increase the return resistance to reduce the internal leakage and delay the service life of the impeller and the pump casing, a seal ring is installed at the inner edge of the pump casing and the impeller foreign aid joint, and the seal gap is preferably maintained between 0.25 and 1.10 mm.

6. The stuffing box is mainly composed of packing, water sealing ring, packing tube, packing gland and water sealing tube. The function of the stuffing box is mainly to close the space between the pump casing and the pump shaft, so that the water in the pump does not flow out and the outside air does not enter the pump. Always keep the vacuum inside the pump! When the friction between the pump shaft and the packing generates heat, it is necessary to rely on the water seal tube to live in the water seal ring to allow the packing to cool! Keep the pump running properly. Therefore, the inspection of the stuffing box during the inspection tour of the pump is of special attention! The packing should be replaced after about 600 hours of operation.