A screw pump is a positive displacement rotor pump that utilizes a screw that engages with a bushing or other screw to form a sealed cavity that transports liquid from the suction end to the discharge end. There are two types of screw pumps: single-screw pumps and multi-screw pumps, and multi-screw pumps can be divided into twin-screw pumps, three-screw pumps, and five-screw pumps.
The different types of screw pumps have their pros and cons, here are some common comparisons
Single screw pump
Single screw pumps consist of a cylindrical screw with external teeth and an oval sleeve with internal teeth. When the screw rotates, a series of closed spaces are formed inside the sleeve, which starts from the suction port and moves along the helix to the discharge port, pushing the liquid out.
Single screw pump has the following advantages
1) Simple structure, easy to install and maintain.
2) It can transport liquids with high viscosity and solid particles or fibers without destroying the structure and properties of the liquid.
3) Smooth flow, no pulsation, low noise, and vibration.
4) It has a self-priming ability and can overcome the air resistance in the pipeline.
5) Multi-stage series can be realized to increase the delivery pressure.
Single screw pumps also have the following disadvantages
1) The efficiency is low, about 30%~40%.
2) Due to the sliding friction between the sleeve and the screw, the wear is fast, and the seal needs to be replaced frequently.
3) Liquid containing hard impurities such as sand grains cannot be transported, otherwise, it will accelerate wear and block.
4) Do not transport volatile or flammable liquids, otherwise, it will cause safety hazards.
Single screw pumps are widely used in petroleum, chemical, food, pharmaceutical, papermaking, construction, environmental protection, and other industries, mainly used to transport oil, emulsion, sewage, sludge, slurry, fruit juice, milk, beer, soy sauce, and other liquids.
Twin screw pump
A twin screw pump consists of two intermeshing co-rotating screws and housing surrounding them. When the two screws rotate, a series of closed spaces are formed inside the housing, which starts from the suction port and moves axially to the discharge port to push the liquid out.
Twin screw pumps have the following advantages
1) Twin-screw pump has a good self-priming ability, can transport multi-phase fluid containing gas or solid particles, and is suitable for medium with high viscosity, high temperature, high pressure, and easy crystallization.
2) The flow rate of the twin-screw pump is directly proportional to the speed, and the precise control of the flow rate can be realized by adjusting the speed, and the step-less speed regulation can also be realized through the frequency converter.
3) The conveying process of the twin-screw pump is smooth, without pulsation, without stirring, with little vibration, low noise, and little impact on pipelines and valves, which protects the nature and integrity of the medium.
4) The structure of the twin-screw pump is simple, compact, and light, with a small footprint, easy installation and maintenance, and long service life. There is no mechanical contact between the twin screws, less wear, and high efficiency.
Disadvantages of twin screw pumps
1) The manufacturing cost of the twin-screw pump is relatively high, and the price is relatively expensive, and it is generally suitable for special requirements or high-end markets.
2) The twin-screw pump has high requirements for the cleanliness of the medium, and it cannot transport liquids containing large particles or strong abrasiveness, otherwise it will accelerate the wear of the screw and the pump body, affecting the performance and life of the pump.
Application of twin screw pump
1) Petroleum industry: Twin-screw pumps can be used in crude oil extraction, transportation, storage, and processing, to transport crude oil, heavy oil, diesel, gasoline, and other oil products with various viscosities and temperatures, and to transport multi-phase products containing water, gas, etc. fluid.
2) Chemical industry: Twin-screw pumps can be used in the chemical production process to transport various chemicals and solvents, such as acids, alkalis, salts, esters, alcohols, phenols, etc., and can also transport easily crystallized or perishable media, such as Syrups, resins, dyes, etc.
3) Papermaking industry: Twin-screw pumps can be used in the papermaking process to transport various pulps and coatings, such as mechanical pulp, chemical pulp, waste paper pulp, etc., and can also transport liquids containing fibers or fillers.
4) Food industry: Twin-screw pumps can be used in food processing to transport high-viscosity non-Newtonian fluids such as chocolate pulp, starch paste, molasses, and pulp
Three screw pump
The three-screw pump is a rotary positive displacement pump, which consists of a driving screw and two driven screws. A sealed working chamber is formed between the three screws. When the driving screw rotates, the driven screw also rotates. Transports liquid from suction to discharge. Three-screw pumps have the following advantages, disadvantages, and applications
Advantages of three screw pumps
1) Smooth flow, no pulsation, low noise, and vibration.
2) The transmission pressure is high, up to 100MPa or more.
3) Wide range of transfer viscosity, from 1cSt to 10000cSt.
4) Compact structure, small footprint, and lightweight.
6) Long life and easy maintenance.
Disadvantages of three screw pumps
1) The cleanliness of the liquid is high, and the liquid containing solid particles or fibers cannot be transported.
2) The temperature of the liquid is high, and it cannot transport superheated or supercooled liquid.
3) It has high requirements on the chemical properties of the liquid, and cannot transport flammable, explosive, oxidizable, or corrosive liquids.
Application of three screw pump
1) Petrochemical industry: used to transport various oil products, lubricating oil, fuel oil, diesel oil, liquefied petroleum gas, etc.
2) Paper industry: used to transport pulp, paper pulp, glue, ink, etc.
3) Food industry: used to transport milk, beverages, fruit juices, beer, soy sauce, vinegar, etc.
4) Machinery industry: used to transport coolant, cutting fluid, hydraulic oil, etc.
5) Shipping industry: used to transport seawater, fresh water, fuel oil, etc.
6) Other industries: used to transport various chemicals, pharmaceuticals, dyes, etc.