What is a liquid ring vacuum pump, and why is it a popular choice across industry?

A liquid ring vacuum pump is a positive displacement pump commonly used for handling wet gases, vapours and liquid carryover across a broad range of industrial applications. A proven and highly reliable vacuum solution, liquid ring vacuum pumps are often the preferred choice in environments where alternative vacuum technologies may struggle to perform effectively.

This guide explains how liquid ring vacuum pumps operate, their typical applications, key advantages and limitations, and the factors to consider when selecting the right pump.

What Is a Liquid Ring Vacuum Pump?

A liquid ring vacuum pump generates a vacuum using a rotating sealing liquid rather than close mechanical tolerances or oil-lubricated vanes. Within the pump casing, a sealing liquid – most commonly water – forms a rotating ring that creates the compression chambers required to draw in, compress, and discharge gas. This straightforward yet highly effective operating principle makes liquid ring vacuum pumps particularly suitable for applications involving moisture, vapours, condensable gases, and contaminated process streams.

Because the process gas does not come into contact with oil and the pump operates without tight internal clearances, liquid ring vacuum pumps offer exceptional tolerance to demanding operating conditions.

How Does a Liquid Ring Vacuum Pump Work?

The operating principle of a liquid ring vacuum pump is relatively simple:

• The pump casing is partially filled with a sealing liquid – just half full
• An impeller mounted eccentrically within the casing rotates
• Centrifugal force drives the liquid outward, forming a rotating liquid ring against the casing wall
• The offset position of the impeller creates chambers of varying volume between the impeller blades and the liquid ring
• As the chamber volume increases, gas is drawn into the pump through the inlet port
• As the chambers decrease in volume, the gas is compressed and discharged through the outlet port

The liquid ring simultaneously acts as a seal, compression medium, and cooling mechanism, contributing to the pump’s robust and reliable performance.

Typical Applications for Liquid Ring Vacuum Pumps

Liquid ring vacuum pumps are widely used in processes where moisture, vapours, or fluctuating operating conditions are present. Common applications include:

• Chemical processing – distillation, evaporation, and solvent recovery
• Pharmaceutical manufacturing – drying, filtration, and deaeration processes
• Food and beverage production – vacuum processing and packaging, drying and evaporation operations
• Pulp and paper manufacturing – dewatering and sheet-forming processes
• Plastic extrusion – removing harmful vapours and eliminating gas bubbles
• Power generation – condenser evacuation and air extraction
• Wastewater treatment – vapour extraction and gas handling
• General industrial vacuum systems – where reliability and process tolerance are critical

In many of these applications, liquid ring vacuum technology is selected specifically because alternative pump types may experience reduced performance, increased maintenance, or premature failure.

Key Advantages of Liquid Ring Vacuum Pumps

Excellent Handling of Wet and Condensable Gases

Liquid ring vacuum pumps are particularly well suited to applications involving steam, saturated gases, and condensable vapours. Unlike many other vacuum technologies, internal condensation does not negatively affect performance and is often an expected part of operation.

Oil-Free Vacuum Generation

As the sealing medium is liquid rather than oil, there is no risk of oil contamination within the process gas stream. This makes liquid ring pumps suitable for applications where product purity is important.

Simple and Robust Design

With relatively few moving components and no metal-to-metal contact within the pumping chamber, liquid ring vacuum pumps offer long service life and dependable operation under demanding conditions.

Quiet and Low-Vibration Operation

The liquid ring naturally absorbs vibration and dampens noise, resulting in quieter operation compared with many alternative vacuum pump technologies.

Low Maintenance Requirements

Routine maintenance is generally limited to bearings, mechanical seals, and monitoring of the sealing liquid. Internal wear is typically minimal, reducing the need for frequent overhauls.

Limitations to Consider

While liquid ring vacuum pumps offer significant advantages, they may not be the ideal solution for every application.

Limited Ultimate Vacuum

Single-stage liquid ring vacuum pumps typically achieve vacuum levels down to approximately 30–33 mbar absolute – the biggest reason for premature failure is when this isn’t controlled and exceeded. Applications requiring deeper vacuum levels may require alternative technologies or multi-stage configurations.

Sealing Liquid Management

The supply, cooling, treatment, and disposal or recirculation of the sealing liquid must be considered during system design and operation. Historically, when water was a cheap commodity, ‘once through’ flush was common place. Today, rising water and effluent treatment costs make this approach expensive. However, modern ‘plug and play’ systems give options for partial or full recirculation, reducing service liquid and effluent costs.

Efficiency Considerations

Pump efficiency can be affected by increases in sealing liquid temperature and vapour pressure, which may reduce achievable vacuum levels and overall performance. Understanding these factors early in the selection process helps ensure the most appropriate vacuum solution is chosen.

Frequently Asked Question

Can Liquid Ring Vacuum Pumps Handle Dirty or Wet Gases?

Yes. One of the primary advantages of liquid ring vacuum pumps is their ability to handle wet gases, condensable vapours, and small quantities of liquid carryover without compromising reliability or performance. This makes them particularly suitable for challenging industrial processes where other vacuum technologies may be vulnerable to damage.

Selection and Operating Considerations

To maximise performance and reliability, consider the following when selecting and operating a liquid ring vacuum pump:

• Monitor and maintain sealing liquid temperature, as warmer liquids reduce achievable vacuum levels
• Select materials of construction appropriate for the process media, particularly in corrosive applications
• Consider liquid recovery or recirculation systems to minimise water consumption and operating costs
• Avoid oversizing the pump, as correct sizing improves efficiency and system performance
• Ensure the pump doesn’t operate below maximum vacuum conditions
• Ensure adequate installation space for maintenance access and servicing

Effective pump selection requires a thorough understanding of both the process requirements and the operating environment.

Pompetravaini Pumps from CDR Pumps (UK) Ltd

CDR Pumps (UK) Ltd works in partnership with Pompetravaini, a leading Italian manufacturer of liquid ring vacuum pumps, centrifugal pumps and side channel pumps. Established in 1929, Pompetravaini now manufactures more than 16,000 units per year.

With flow rates of up to 30,000 m3/hr, vacuum pressures down to 33 mbar with the addition of own brand blowers, and the ability to incorporate vacuum pumps into full ‘plug and play’ vacuum systems, CDR Pumps (UK) Ltd can provide a liquid ring vacuum pump solution to most applications.

To discuss a liquid ring vacuum pump solution for your application, contact the specialist team at CDR Pumps (UK) Ltd on 01933 674777 or at sales@cdrpumps.co.uk