Screw pump has a wide range of applications, which is characterized by steady flow, small pressure fluctuation, self-priming ability, low noise, high efficiency, long life, small size and reliable operation. The outstanding advantage is that when conveying the medium, it does not form eddy current and can transport various media with a wide range of viscosity, which can transport not only lubricating or corrosive media with various viscosity, but also non-Newtonian liquids with various viscosities, as well as gas-liquid mixed transportation and solid-liquid mixed transportation. It is widely used in offshore platform engineering, petrochemical industry, shipping, electric power, mechanical hydraulic system, food, paper, sugar, military and sewage treatment and other industrial sectors.
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Of course, it is not that a certain kind of screw pump can transport all the media, but different types can be selected according to the characteristics of the media and the number of performance parameters. Screw pump is usually divided into single-screw pump, double-screw pump, three-screw pump and five-screw pump according to the number of screws, each has its own advantages, and there must be a choice in popularization and application. Only by making full use of their respective characteristics, can we better achieve energy saving, material saving, increase efficiency or meet some special requirements. The pump sleeve of the single screw pump is made of non-metallic elastic material (usually rubber). The inner hole is in the shape of a spiral groove, and a number of sealing cavities are formed between it and a spiral metal screw. The metal screw moves eccentrically to shift the sealing cavity from the low pressure area of the pump to the high pressure area, completing the whole process of suction, discharge and pressure formation. In addition to general media, it can transport suspensions and special media containing metal particles, fibers and so on. In the treatment of sewage, mud, commonly used single screw pump, usually the working pressure is not high.
The three-screw pump is a strictly sealed screw pump in theory. In textbooks, it is usually introduced as a typical example of screw pump. The three-screw pump is composed of two driven screws driven by a main screw in the metal pump sleeve. Each screw has two helical lines, and a number of sealing cavities are formed between the pump sleeve and the screw. When the screw rotates, the sealing cavity moves from the low pressure area of the pump to the high pressure area. The maximum working pressure of the three-screw pump can reach 30MPa, and the conveying medium is clean and non-corrosive lubricating oil, which can transport high viscosity and non-corrosive medium (such as ink, glue, etc.) in special occasions. Due to the structural size of the 1:3:5 ratio of the three screws and other reasons, the viscosity range of the medium conveyed by the three screw pump is limited, which is generally limited to the lubricating medium.
Screw pump is widely used in sewage treatment plants to transport water, wet sludge and flocculant liquid because of its variable transport, strong self-priming capacity, reversible and capable of transporting liquid containing solid particles. Selection should follow the principles of economy, rationality and reliability. If the design and type selection is not considered carefully, it will bring trouble to the future use, management and maintenance, so choosing a reasonable and reliable screw pump according to the actual needs of production can not only ensure the smooth production, but also reduce the repair cost.
