Introduction to the selection characteristics of the working principle of the single screw pump
1. Working principle of single screw pump. Single screw pump is a rotor type positive displacement pump, which relies on the screw and bushing to mesh with each other to produce volume changes in the suction cavity and discharge cavity to transport liquid. It is a closed screw pump with internal meshing. The main working parts are composed of a bushing (stator) with a double-head spiral cavity and a single-head spiral screw (rotor) meshed with the stator cavity. When the input shaft drives the rotor through the universal joint to make a planetary rotation around the center of the stator, the stator-rotor pair is continuously meshed to form a sealed cavity. The volume of these sealed cavities will move in an axial direction at a constant speed and transfer the medium from the suction end through the stator. — The rotor pair is transported to the extrusion end, and the medium sucked into the closed cavity flows through the stator without being agitated or damaged. The screw has a single-head thread, and its arbitrary cross-section is a circle with a radius of R. The center of the cross-section is on the spiral line and deviates from the axis of the screw by an eccentric distance e. The number of heads formed by rotating around the axis and moving in the axial direction Than Lobes: The number of stator heads T1 of the screw is one more than the number of rotor heads T2, that is, T1=T2+1. Their ratio becomes the top number ratio. Screw pumps can be divided into single-head (1:2) and multi-head (2:3, 3:4) and so on. The more the head number ratio, the greater the output torque of the screw pump and the lower the speed. Conversely, the smaller the output torque, the higher the speed. The inner surface of the bushing has double threads, any cross-section of which is an oblong circle, both ends are semicircles with a radius of R (equal to the cross-sectional radius of the screw), and the middle is a straight line segment with a length of 4e. Any cross-section of the bushing is the same ellipse, but they are mutually offset by an angle. After the screw is installed in the bushing, a closed cavity is formed between the screw surface and the inner thread surface of the bushing. At the same time, any cross-section is also divided into two crescent-shaped working rooms (as shown in Figure 1-3). When the screw rotates, the volume of the first working chamber close to the suction chamber gradually increases, forming a negative pressure, and the liquid is sucked into the working chamber under the action of the pressure difference. As the screw continues to rotate, after the volume of the working chamber continues to increase to the maximum, the working chamber is closed and the liquid is pushed out of the chamber in the axial direction. At the same time, the upper and lower working chambers suck and discharge the liquid alternately, so the liquid is continuously pushed from the suction chamber to the pressure out chamber in the axial direction.
2. Features of single screw pump Because of its structure and working characteristics, screw pump has many advantages compared with piston pump centrifugal pump, vane pump and gear pump: 1. It can transport high solid content media; 2. The flow is uniform and the pressure is stable. It is more obvious at low speed; 3. The flow rate is proportional to the speed of the pump, so it has good variable adjustability; 4. One pump can be used for multiple purposes to transport media with different viscosities; 5. The installation position of the pump can be inclined at will; 6. Suitable Convey sensitive items and items that are easily damaged by centrifugal force; 7. Small size, light weight, low noise, simple structure and convenient maintenance.
3. Selection of single screw pump The specification of the pump is determined according to the nature, flow and pressure of the liquid to be transported, and the speed of the pump is selected by the viscosity and corrosiveness of the liquid to be transported as the main parameter to ensure the reliability of the pump. run. The design speed of the pump is the highest speed allowed when transporting clean water or similar non-corrosive liquids. In actual use, due to the different nature of the medium and the life requirements, the selection should generally be lower than the design speed. For high-viscosity and particle-containing media, generally use 1/2-1/3 or lower of the design speed. Low speed is beneficial to the wear of the pump, but after use, the flow rate of the stator will decrease, so the speed can be appropriately increased. It is also a common policy to compensate for the drop in flow. The temperature of the conveying medium should be between -10 ℃ and 80 ℃, and can be as high as 120 ℃ under special circumstances. The normal pressure of each stage of the pump (a lead of the stator) is 0.6Mpa, and it is allowed to be as high as 0.8Mpa in a short time (no more than 30 minutes). The volumetric efficiency at the same output pressure will gradually decrease after wear. When pumping clean water, the maximum suction stroke is 8 meters. The actual use is recommended not to exceed 6.5 meters. When pumping high-viscosity media, the suction should be positive pressure.
