Liquid Ring Vacuum Pumps

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A liquid-ring pump is a rotating positive-displacement pump. They are typically used as a vacuum pumpbut can also be used as a gas compressor. The function of a liquid-ring pump is similar to a rotary vane pumpwith the difference being that the vanes are an integral part of the rotor and churn a rotating ring vacuum pump liquid ring liquid to form the compression-chamber seal.

They are an inherently low-friction design, with the rotor being the only moving part. Sliding friction is limited to vacuum pump liquid ring shaft seals. Liquid-ring pumps are typically powered by an induction motor. The liquid-ring pump compresses gas by rotating a vaned impeller located eccentrically within a cylindrical casing.

Liquid usually water is fed into the pump and, by centrifugal acceleration, forms a moving cylindrical ring against the inside of the casing. This liquid ring creates a series of seals in the space between the impeller vanes, vacuum pump liquid ring form compression chambers. The eccentricity between the impeller's axis of rotation and the casing geometric axis results in a cyclic variation of the volume enclosed by the vanes and the ring. Gas, often air, is drawn into the pump through an inlet port in the end of the casing.

The gas is trapped in the compression chambers formed by vacuum pump liquid ring impeller vanes and the liquid ring. The reduction in volume caused by the impeller rotation compresses the gas, which reports to the discharge port in the end of the casing.

Compressed gas on discharge of pump contains certain amount of working liquid which is usually removed in vapor—liquid separator. The earliest liquid-ring pumps date fromwhen a patent was granted in Germany to Siemens-Schuckert. US Patent 1,, for liquid-ring vacuum pumps and compressors, was granted to Lewis H. Around the same time, in Austria, Patent was granted to Siemens-Schuckertwerke for a similar liquid-ring vacuum pump. Liquid-ring systems can be single- or multistage.

Typically a multistage pump will have up to two compression stages on a common shaft. In vacuum service, the attainable pressure reduction is limited by the vapour pressure of the ring-liquid. As the generated vacuum approaches the vapour pressure of the ring-liquid, the increasing volume of vapor released from the ring-liquid diminishes the remaining vacuum capacity. The efficiency of the system declines as a result.

Single-stage vacuum pumps typically produce vacuum to 35 Torr mm Hg or 47 millibars 4. Some ring-liquid is also entrained with the discharge stream. This liquid is separated from the gas stream by other equipment external to the pump. In some systems, vacuum pump liquid ring discharged ring-liquid is cooled by a heat exchanger or cooling towerthen returned to the pump casing. In some recirculating systems, contaminants vacuum pump liquid ring the vacuum pump liquid ring become trapped in the ring-liquid, depending on system configuration.

These contaminants become concentrated as the liquid continues to recirculate, eventually causes damage and reduced life to the pump. In this case, filtration systems are required to ensure that contamination is kept to acceptable levels.

In non-recirculating systems, the discharged hot liquid usually water is treated as a waste stream. In this case fresh cool water is used to make up the loss. Environmental considerations are making such "once-through" systems increasingly rare. These simple, but highly reliable pumps have a variety of industrial applications. They are used to maintain condenser vacuum on large steam-turbine generator sets by removing incondensable gasses, where vacuum levels are typically 30—50 mbar.

They are used on paper machines to dewater the pulp vacuum pump liquid ring and to extract water from press felts. Another application is the vacuum forming of molded paper-pulp products egg cartons and other packaging.

Other applications include soil remediation, where contaminated ground water is drawn from wells by vacuum. In petroleum refining, vacuum distillation also makes use of liquid-ring vacuum pumps to provide the process vacuum. Liquid-ring compressors are often used in vapor recovery systems.

Liquid-ring vacuum pumps can use any liquid compatible with the process, provided it has the appropriate vapor pressure properties, as the sealant liquid. Although the most common sealant is water, almost any liquid can be used. The second most common is oil. Since oil has a very low vapor pressure, oil-sealed liquid-ring vacuum pumps are typically air-cooled.

For dry chlorine gas applications concentrated sulfuric acid is used. The ability to use vacuum pump liquid ring liquid allows the liquid-ring vacuum pump to be ideally suited for solvent vapor recovery. If a process, such as distillation or a vacuum dryer, is generating toluene vapors, for example, then it is possible to use toluene as the sealant, provided the cooling water is cold enough to keep the vapor pressure of the sealant liquid low enough to pull the desired vacuum.

Ionic liquids in liquid-ring vacuum pumps can lower the vacuum vacuum pump liquid ring from about 70 mbar to below 1 mbar. From Wikipedia, the free encyclopedia. Ionic liquids — designable materials for high-performing fluids.

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From the outside, the NASH vacuum pump only hints at how it's internal parts function. Shaft bearings on heavy cast iron brackets are easily accessible for servicing.

The top connection of the pump is the inlet, while the side connection is its discharge some NASH pumps do have a different orientation. The NASH liquid ring vacuum pump uses water or any other suitable liquid, which acts as "liquid pistons", hence the name liquid ring.

It's apparent that the chambers between the rotor blades, shown here in yellow, are open around the periphery.

The chambers are open on the inside, as well. These inner edges of the rotor blades are machined to rotate around the cone surface, shown in red , with a close non-contact fit. An internal passage joins the openings from the pump inlet to an inlet port in the cone. There's also a passage from the cone discharge to the discharge connection on the head. Some NASH pumps have a port plate configuration rather than conical, but the principle is the same.

This diagram demonstrates what the rotor and body do while the pump is in operation. The spinning of blue liquid forms a ring due to centrifugal force. Because the rotor axis and body axis are offset from each other, the liquid ring is not concentric with the rotor. Air or gas traverses the internal passage to the cone inlet port. As the white dots indicate, the gas is drawn into the rotor chambers by the receding liquid ring, similar to the suction stroke of a piston in a cylinder.

The liquid ring does the job of pistons, while the rotor chambers play the part of cylinders. As each chamber rotates past the inlet port, the chamber carries a volume of air or gas around with it. The white dots are confined between the cone and the ring of rotating liquid. The gas is compressed as the liquid ring converges with the cone. This represents the compression of air or gas from vacuum up to atmospheric pressure, or from atmospheric up to positive pressure in a liquid ring compressor.

When each chamber rotates to the discharge port opening, the compressed air or gas escapes from that chamber through the discharge port to the internal discharge passage.

Air or gas, with the dots closely packed to indicate higher pressure, is shown here flowing out of the discharge connection at right. The flow is continuous without pulsation. In this completed schematic, the entire vacuum pumping cycle is shown. Here air or gas entering the NASH pump is shown as white dots at the inlet connection.

This represents the compression of air or gas from vacuum up to atmospheric pressure, or from atmospheric up to positive pressure in a liquid ring compressor Discharge 9. Learn more about the liquid ring principle from Nash, the original liquid ring innovator.