Definitions and Types

Definition: A liquid-ring vacuum pump is a rough‑vacuum pump that achieves suction, compression, and exhaust through changes in the pump chamber’s volume. It is a positive‑displacement vacuum pump, capable of pumping both gas and liquid, though it is primarily used for gas evacuation.

Type:

Single-stage, single-acting liquid-ring pump: It has only one impeller; for each revolution of the impeller, suction and discharge occur once. It achieves a relatively high ultimate vacuum but exhibits lower pumping speed and efficiency.

Single-stage double-acting liquid-ring pump: It features a single impeller; with each revolution, it completes two suction strokes and two discharge strokes. At the same pumping speed, it is compact and lightweight, offers higher pumping speed and efficiency, but has a lower ultimate vacuum.

Two-stage liquid-ring pump: Typically composed of single-stage pumps connected in series, with two single-stage, single-acting impellers sharing a common shaft. It maintains a high pumping speed even at elevated vacuum levels and operates with stable performance.

Atmospheric water‑ring pump: a unit consisting of an atmospheric ejector in series with a water‑ring pump, used to enhance the ultimate vacuum and broaden the range of applications.

Working principle

The pump housing contains an appropriate amount of water as the working fluid, and the impeller is mounted eccentrically within a circular chamber. As the impeller rotates, the water, under centrifugal force, forms a nearly uniform‑thickness closed ring—the liquid ring. The inner surface of the upper portion of the liquid ring is tangent to the impeller hub, while the inner surface of the lower portion contacts the blade tips. Between the impeller hub and the liquid ring, a crescent‑shaped space is created, which the impeller divides into several small chambers. During the first 180° of impeller rotation, the volume of each chamber increases, connecting with the suction port and allowing gas to be drawn in; at the end of suction, the chamber is sealed off from the suction port. As the impeller continues to rotate, the chamber’s volume decreases, compressing the gas; when the chamber connects with the discharge port, the compressed gas is expelled from the pump.

Structural Composition

A typical structure comprises an air inlet, an air outlet, a pump cover, a pump housing, an impeller, a partition plate, and an electric motor. The impeller consists of multiple blades evenly distributed in a radial pattern and a hub, and is mounted eccentrically within the working chamber.

Performance Features

Advantages:

It has a simple structure, requires low manufacturing precision, and is easy to machine.

Compact structure, high rotational speed, direct coupling with the motor, and a small footprint.

Compressed gases undergo nearly isothermal compression, and flammable or explosive gases can be evacuated.

The pump chamber contains no metal‑to‑metal friction surfaces, requires no lubrication, exhibits minimal wear, and employs a water seal to ensure sealing between rotating and stationary components.

It features uniform air intake, stable and reliable operation, simple handling, and convenient maintenance.

Disadvantages:

Efficiency is low, typically around 30%, with occasional improvements up to 50%.

When the vacuum level is low and water is used as the working fluid, the ultimate pressure typically ranges from 2,000 to 4,000 Pa (limited by the saturation vapor pressure of the working fluid).

Main Models and Features (Partial)

Type 2BA:

It is suitable for pumping gases and water vapor, with a suction pressure as low as 33 mbar absolute (97% vacuum). When oil is used as the working fluid, the suction pressure can reach 6.7 mbar absolute (99.3% vacuum), making it a viable replacement for reciprocating vacuum pumps.

The pump and motor feature a coaxial direct‑drive design, saving space and simplifying installation; all units are equipped with imported mechanical seals; a cavitation‑protection pipe connection is provided; the aluminum‑bronze impeller offers high strength and excellent corrosion resistance, while flow‑path components can be made of stainless steel; a unique flexible venting port design ensures superior efficiency; Y2‑series motors with a high protection rating are used; and imported bearings are employed.

Type 2BE:

Single-stage, single-acting design, suitable for pumping gases that contain no solid particles, are insoluble in water, and are non-corrosive; with material modifications, it can also handle corrosive gases or use corrosive liquids as the working fluid.

The bearings are original imported units, ensuring impeller alignment and operational stability; the impeller is made of ductile cast iron or welded steel plate, offering a long service life; the pump casing is fabricated from steel plate; the shaft sleeve is crafted from high‑chromium stainless steel, further extending its lifespan; the pulley (for belt drive) is a standard, high‑precision tapered‑bush pulley, while the coupling (for direct drive) is a standard, high‑strength flexible coupling; the top‑mounted air–water separator saves space and reduces noise; and the castings are produced using resin‑bonded sand molding, delivering excellent surface quality.

Application areas

It is widely used in numerous industries, including petroleum, chemical engineering, light industry, pharmaceuticals, food processing, metallurgy, building materials, power generation, and environmental protection, for processes such as vacuum filtration, vacuum water priming, vacuum material feeding, vacuum evaporation, vacuum concentration, vacuum degassing, gas recovery, and flue‑gas desulfurization.