The working principle and application fields of vacuum pumps

A vacuum pump is a device that uses various methods to generate, improve, and maintain vacuum in a closed space.

A vacuum pump can be defined as a device or equipment that uses mechanical, physical, chemical, or physicochemical methods to extract air from the container being pumped and obtain a vacuum.

With the development of vacuum applications, there have been many types of vacuum pumps, with pumping speeds ranging from a few tenths of a second to hundreds of thousands or millions of liters per second. Extreme pressure (ultimate vacuum) ranges from coarse vacuum to extremely high vacuum above 10-12Pa.

The principle of liquid ring pump

Liquid ring vacuum pump is a type of coarse vacuum pump, which is equipped with a multi blade rotor eccentrically installed inside the pump casing. When it rotates, it throws the liquid towards the pump casing and forms a liquid ring concentric with the pump casing. The liquid ring, together with the rotor blades, forms a rotating variable volume vacuum pump with periodic volume changes.

The metal cavity is located inside the circular pump body (A) and is equipped with an impeller (B) on an eccentric shaft relative to the centerline of the pump body. The centrifugal action of the rotating impeller forces the working fluid to flow through the channel (D) to the periphery of the cavity, forming a circulation (C). When the pump is activated, the transported gas mixture enters the impeller through the suction port (H) on the intermediate plate (E), and a vacuum is formed at the pump inlet.

The gas mixture is filled into the impeller chamber located between the inner diameter of the liquid ring and the root of the impeller blade. When the impeller rotates, the degree of immersion of the impeller blade in the liquid ring increases, and the volume between the liquid ring and the root of the impeller blade decreases. As a result, the gas mixture is compressed until it reaches the discharge port (J) in the intermediate plate (K), and the gas mixture is discharged through the discharge port.

During the compression cycle, heat is transferred to the liquid ring, and cooling is necessary to maintain the temperature below the evaporation point of the working liquid. Cooling is achieved by continuously adding cold working fluid to the liquid ring.

The amount of working fluid added is equal to the amount of working fluid discharged together with compressed gas mixture through the discharge port, and the gas mixture and working fluid are finally separated through the pump outlet.

Application of liquid ring pump

Applications in pulp and paper production: black liquor evaporation, coarse pulp washing machine, lime slurry and filter, sediment filter, vacuum dewatering machine, raw material and white water degassing system, mixing box compressor, suction water tank, pressure roller, suction and transfer roller, vacuum pressing, woolen cloth suction water tank, anti blow box.

Application in the plastic industry: extruder degassing, shaping table (profile), EPS foaming, drying, pneumatic conveying device, vinyl chloride gas extraction and compression.

Applications in instruments: steam sterilization, respiratory devices, air cushions, protective clothing, dental instruments, central vacuum systems.

Applications in the food and beverage industry: salmon cleaning machine, mineral water degassing, salad oil and fat deodorization, tea and seasoning sterilization, sausage and ham production, tobacco product humidification, vacuum evaporator.

Applications in other industries, etc.

2、 Claw type vacuum pump

The principle of claw pump

The claw type dry oil-free vacuum pump has several sets of meshing claw type rotors in the pump chamber. There is no contact between the rotor and the pump chamber, leaving a small gap and no need for any lubricant, thus ensuring a clean vacuum environment.

The structure of the pump adopts a multi-stage rotor series connection, with each group of rotors located in different pump chambers for synchronous reverse movement.

The pump chamber is separated by a claw shaped rotor into two parts: the suction chamber and the exhaust chamber. With the continuous operation of the rotor, a cyclic suction and exhaust process is carried out, achieving the goal of continuous pumping.

The application of claw pumps

Petrochemical industry:

Capable of removing acidic gases such as tetrahydrofuran; Capable of removing condensable gases such as alcohol, gasoline, etc; Capable of extracting flammable and explosive gases such as oxygen, hydrogen, methane, etc; The anti-corrosion series can remove strong acidic gases such as hydrogen chloride gas, sulfuric acid gas, etc.

Pharmaceutical industry:

Crystallization, distillation, sublimation, drying, deodorization, polymerization, vacuum evaporation, negative pressure filtration, monomer recovery, adsorption/desorption, material transportation, corrosive media, ethylene oxide disinfection, etc.

Food industry: sublimation, drying, dehydration, vacuum evaporation, vacuum fresh food, vacuum packaging, etc.

Metallurgical industry: impregnation, extrusion, vacuum coating, ion etching, mud degassing, steel degassing, molecular beam epitaxy, etc.

Applications in other industries, etc.

3、 Screw vacuum pump

The principle of screw pump

A screw pump is a high-speed rotation of the left and right screws that engage and do not come into contact with each other through gear transmission and synchronous reverse rotation. The pump casing and the spiral grooves of the meshing screw are separated into multiple spaces, forming multiple stages. Gas is transmitted and moved in equal grooves (cylindrical and equal pitch), but without compression. Only the spiral structure at the end of the screw has a compression effect on the gas.

The pressure gradient can be formed between each stage of the screw to disperse the pressure difference and improve the compression ratio. The clearance between various parts and the pump speed have a significant impact on the performance of the pump. When designing the clearances between various parts of the screw, factors such as expansion, machining and assembly accuracy, and working environment should be considered.

The application of screw pumps

Screw dry vacuum pumps are widely used in fields such as electronics, nuclear energy, chemical, pharmaceutical, and food industries.

The CVD process used in the semiconductor industry for chip production, LCD display manufacturing, etching, and PLASMA production.

Used in nuclear reactors and vacuum acquisition in the nuclear industry; In chemical industry, it is used for efficient recovery of solvents through vacuum distillation and solvent extraction. In fatty acid production, it is used to eliminate water pollution and remove blockages in injectors; Used in the pharmaceutical industry for the recovery of pharmaceutical liquids and intermediates, as well as for the recovery of gas disinfectants; In the food industry, it is used for flavor, essence concentration, food packaging, etc. The application range is extremely wide.

The principle of Roots pump

The Roots pump is located in the pump chamber, with two "8" shaped rotors installed perpendicular to each other on a pair of parallel shafts. They are driven by a pair of gear belts with a transmission ratio of 1, which rotate synchronously in opposite directions to each other.

There is a certain gap between the rotors and the metal cavity wall inside the pump casing, which can achieve high-speed operation.

Due to the fact that Roots pump is a vacuum pump without internal compression, the compression ratio is usually very low, so high and medium vacuum pumps require a front stage pump.

The ultimate vacuum of a Roots pump depends not only on the structure and manufacturing accuracy of the pump itself, but also on the ultimate vacuum of the preceding pump. In order to improve the ultimate vacuum pump of the pump, Roots pumps can be used in series.

Application of Roots Pump

Roots vacuum pumps have been tested for long-term operation in petroleum, chemical, plastic, pesticide, turbine rotor dynamic balance, aerospace space simulation and other devices, and are vigorously promoted and applied in China.

At the same time, Roots vacuum pumps are widely used in smelting, degassing, rolling, as well as vacuum distillation, vacuum concentration, and vacuum drying in the food and pharmaceutical industries in vacuum metallurgy. They are also widely used in industries such as smelting, petrochemicals, electrical engineering, electronics, and packaging.