The Versatility of Liquid Ring Vacuum Pumps – from contaminated fluids to priming action
Liquid ring vacuum pumps work on a similar principle to a rotary vane compressor or rotary vane pump. The liquid ring vacuum pump effectively stirs the liquid it is pumping into a vortex, creating a pressure seal without the complexity of diaphragms, valves or a reciprocating element. Liquid ring pumps are simple to operate and therefore low in maintenance as the rotor is the only moving part. They are also efficient because their operation is based on rotary motion rather than reciprocation and their design is inherently low in friction.
Developed over 100 years ago, their design has been steadily refined and today they remain a popular choice for a wide range of applications in many different industries. Standard materials of construction include bronze or stainless steel for the impeller and cast iron or stainless steel for the housing. Other materials such as Hastelloy are also available for special applications.
Liquid ring vacuum pumps comprise of a main body forming a cylindrical pumping chamber, with its axis horizontal. Within this, a vaned impeller is eccentrically mounted (i.e. its axis of rotation does not align with the axis of the chamber; it is parallel to it and somewhat lower). Inlet and outlet ports are located in the flat endplates with their positioning being very important.
Product Download Operation In use, vacuum pumps are about half-full with liquid and the rotation of the impeller churns it into a vortex-type motion around the wall of the pumping chamber. The spinning liquid effectively seals the space between each pair of adjacent vanes into individual cells.
The cells vary in size as they rotate through a complete revolution. At the very bottom the length of the cell is equal to the radius of the chamber less the distance of eccentricity; at the top it is equal to the radius of the chamber plus the distance of eccentricity.
As a cell rotates upward from the bottom, its length increases which reduces the pressure within it. Conversely, on the second half of the rotation, the cell is descending and its length is reducing, which pressurises the cell.
The inlet port is located on the upstroke side of the rotation, so that the reducing pressure sucks fluid into the chamber. A short time later it is pumped out of the chamber through the outlet port located 180degs away on the downstroke side.
Liquid ring pumps are available as single-stage or double-stage units. Although theoretically possible, three- and more-stage units are rare. Typically, a two-stage pump has a single shaft and two aligned but separate compression chambers, each with its own impeller.
Typical uses include ancillaries on steam turbines, papermaking machines, groundwater management, vacuum distillation and vapour recovery. They come in a range of sizes, with small ones used on applications in laboratories and larger ones used across many industries. One duty for which they are very popular is priming larger pumps in installations like clean and foul water pumping stations and heavy industries.
EuroVacuum Products supplies both single- and double-stage pumps, the former producing vacuum pressures to 33mbar, and the latter to 0.5mbar. Both are available in monobloc, lantern and bare shaft versions and in a range of sizes.
Their design allows the use of oil as a service liquid without the need for compromise in efficiency. At the same time they can handle contaminated fluids, which makes them highly reliable in applications such as abattoirs and sewage works, where hard and relatively large solids are frequently entrained in the process fluid and can cause abrasion.
Furthermore, they are popular in the chemicals and plastics industries, where aggressive fluids are in use. Eurovacuum Products can offer ATEX certified liquid ring systems for most Gas groups IIA and IIB and zone 21 and 22.
Liquid ring pumps are popular with food manufacturers and packers because the constant flushing helps to maintain hygiene standards. It is also notable that limescale does not build up so much in constant flow pumps as it does on reciprocating designs that cyclically stop and reverse the direction of fluid flow.
Plastics industries use vacuum pumps in many ways – to provide non-contact handling of parts, to dry products and degasification materials, for foaming and for laminating sheet materials together. Papermakers use vacuum pumps in their dewatering plants and printers use them for handling of sheets of paper – particularly those that have just been printed and likely to still be wet.
In the medical world, dentists’ drills tend to be vacuum-driven, while liquid ring vacuum pumps are also widely used on sterilisers because of their ability to withstand steam.
Chemical industries use many vacuum pumps for degassing, coating, cooling, impregnating, pneumatic conveying, solvent recovery and even thin film deposition. Even greater use is made in environmental processes, such as biogas production, sewage treatment, water aeration and filtration and liquid recovery.
Operation and installation manual: