The liquid ring vacuum pump is a type of vacuum pump that uses a rotating ring of liquid to seal and compress gas, enabling it to handle gas streams containing moisture, water vapor, or liquid droplets without damage — a challenge that dry vacuum pumps often struggle with. The near-isothermal operating mechanism (temperature remains essentially stable thanks to the working fluid) makes it well suited for humid environments, solvent vapor, or mildly corrosive gas streams across a wide range of industries.
- A liquid ring (typically water) rotates to create a sealed compression chamber — capable of handling gas with moisture and liquid droplets.
- Operates near-isothermally with minimal local heat generation, making it suitable for handling solvent vapor and hot gas streams.
- Simple construction with few dry-friction components, resulting in durability and ease of maintenance in demanding environments.
- VS series by Salvatore Robuschi (Italy): single-stage, flow rate 35–1600 m³/h, vacuum down to 33 mbar, 0.25–400 kW, DN25–125.
- Applications: chemical processing, wastewater treatment, food processing, bioethanol production, textile dyeing, and leather tanning.
Working Principle of the Liquid Ring Vacuum Pump
The Liquid Ring for Sealing and Gas Compression
Inside the pump casing, an impeller is mounted eccentrically relative to the circular chamber, which holds a partial volume of working fluid — typically water. As the impeller rotates, centrifugal force drives the fluid outward against the chamber wall, forming a liquid ring that is concentric with the chamber but eccentric with the impeller shaft. Due to this eccentricity, the volume between the impeller vanes and the liquid ring continuously changes: the expanding volume draws gas in through the inlet port, while the contracting volume compresses and discharges it through the outlet port.
The liquid ring acts as a liquid piston that both seals and compresses, while simultaneously absorbing the heat of compression, keeping the process near-isothermal. This liquid layer allows the pump to “swallow” moisture, liquid droplets, and partially condensed vapor in the gas stream without jamming or overheating — as dry vacuum pumps would. The working water is then separated and replenished in a recirculation loop to maintain stable vacuum.
Why It Is Suited for Gas with Moisture
Handling Water Vapor, Solvent Vapor, and Liquid Droplets
In many real-world processes, the gas stream to be evacuated is not completely dry: water vapor rising from tanks, solvent vapor in evaporation-distillation processes, or liquid droplets carried along. Dry vacuum pumps are prone to failure when vapor condenses onto friction surfaces. In contrast, in a liquid ring pump, the working fluid itself is the medium that receives moisture, so this type of vapor causes no harm and is actually handled along with the recirculating water.
| Criteria | Liquid ring vacuum pump | Dry vacuum pump |
|---|---|---|
| Gas with moisture/liquid droplets | Handles reliably | Prone to condensation issues |
| Thermal characteristics | Near-isothermal thanks to working fluid | Higher compression heat generation |
| Solvent vapor/mildly corrosive gas | Suitable with appropriate material selection | More limited |
| Working fluid | Requires water supply and separation with recirculation | Not required |
The working fluid can be changed from water to another compatible liquid (oil, compatible solvent) when the process requires, extending the range of application to specific vapor streams. Selecting the correct working fluid and pump casing material is the key factor determining service life in corrosive environments.
VS Series Technical Specifications and Selection Guide
Flow Rate Range, Vacuum Level, and Power
When selecting an industrial vacuum pump, three parameters to determine first are: gas intake flow rate (m³/h), required vacuum level (mbar absolute), and the nature of the gas stream (dry or wet, corrosive or not). From there, the appropriate pump range, material, and water supply system can be selected. The VS series by Salvatore Robuschi is a single-stage liquid ring pump with the following specifications:
| Parameter | VS Series (single-stage) |
|---|---|
| Gas intake flow rate | 35–1600 m³/h |
| Vacuum level | Down to 33 mbar |
| Motor power | 0.25–400 kW |
| Connection size | DN25–125 |
The above figures represent the range limits depending on model and actual operating conditions (working water temperature, gas stream humidity, installation altitude). The VS is available in several configurations: compact monobloc close-coupled, as well as long-coupled base-mounted versions for maintenance without disturbing the piping. Depending on requirements, discharge valves and a separation-recirculation water supply assembly can be added to optimize working water consumption.
Applications and Materials
Industry Applications and Material Selection
Liquid ring vacuum pumps are widely used in processes with wet gas or vapor-laden streams: chemical processing, wastewater treatment, food processing, bioethanol production, textile dyeing, and leather tanning. Common tasks include vacuum filtration equipment, evaporation/concentration, vacuum drying, degassing, and industrial gas transfer.
Regarding materials, the Salvatore Robuschi pump series offers options in cast iron, AISI 316, Superduplex, and 904L (with ATEX options for hazardous areas), along with mechanical seals in multiple configurations. For corrosive gas or liquid streams, upgrading to SS316 or higher-alloy materials extends service life. This is also the approach when integrating vacuum pumps into industrial chemical processing systems.
SALVATORE ROBUSCHI · ITALY
Salvatore Robuschi (Italy, part of Gruppo Aturia) is a centrifugal pump manufacturer with a product range spanning process pumps to ISO 2858/ISO 5199, water supply pumps to EN 733, multi-stage pumps, self-priming pumps, and liquid ring vacuum pumps. The VS series is a single-stage liquid ring pump, flow rate 35–1600 m³/h, vacuum down to 33 mbar, 0.25–400 kW, DN25–125, featuring externally replaceable discharge valves, solid gaskets instead of sealant, and lifetime-lubricated bearings. TKT Pumps is the authorized distributor of Salvatore Robuschi in Vietnam — with 19+ years of experience, 12,000+ projects, and 28+ brands, our technical team supports pump range selection, material specification, and recirculation water system design based on actual site conditions.
Frequently Asked Questions
How does a liquid ring vacuum pump work?
+
An eccentrically mounted impeller rotates inside a casing containing liquid (typically water). Centrifugal force drives the liquid to form a sealing liquid ring; the volume between the vanes expands to draw gas in and contracts to compress it, pushing gas out through the discharge port. The liquid ring simultaneously seals and absorbs the heat of compression, keeping the process near-isothermal.
Why can this type of pump handle gas with moisture?
+
Because the working fluid inside the pump receives the moisture and liquid droplets carried along in the gas stream, rather than allowing them to condense onto dry friction surfaces. As a result, water vapor, solvent vapor, or liquid droplets do not cause damage as they would in a dry vacuum pump, making it well suited for humid environments.
What vacuum level and flow rate does the VS series achieve?
+
The VS series by Salvatore Robuschi is a single-stage liquid ring pump with gas intake flow rate 35–1600 m³/h, vacuum down to 33 mbar, power 0.25–400 kW, and connection size DN25–125. These are range limits; actual specifications depend on the model and operating conditions.
Does a liquid ring pump require a continuous water supply?
+
Yes. The working fluid must be supplied and replenished to maintain the sealed ring and vacuum level. In practice, a separation and recirculation water supply assembly is typically used to reduce working water consumption, enabling more stable and economical operation.
Can it be used for corrosive gas streams?
+
Yes, with the correct material selection. The Salvatore Robuschi pump series offers options in cast iron, AISI 316, Superduplex, and 904L, along with ATEX options, suitable for gas and liquid streams of varying corrosiveness. It is advisable to discuss the operating conditions in detail to select the appropriate material configuration and mechanical seal.
Should I choose a liquid ring pump or a dry pump?
+
If the gas stream is wet, contains solvent vapor, or carries liquid droplets, a liquid ring pump is generally more suitable due to its ability to handle moisture and its near-isothermal characteristics. If the gas stream is dry and requires no working fluid, a dry pump may be appropriate. The selection should be based on flow rate, vacuum level, and the nature of the gas stream.
Need advice on selecting a liquid ring vacuum pump based on your actual flow rate, vacuum level, and gas stream requirements?
Send a Consultation Request or hotline 0941.400.488
Source: Salvatore Robuschi technical documentation (VS series — liquid ring vacuum pump) and centrifugal pump engineering knowledge; compiled by TKT.
