MechChem Africa June 2018

Air & Vacuum Technologies, based in Midrand, Gauteng is a leading provider of a wide range of equipment to all parts of South & Southern Africa. Here outlined is the liquid ring vacuum pump (LRVP) and its uses. The liquid ring vacuum pump

A liquid-ring pump is a rotating positive-displacement pumpwhich istypicallyusedasavacuumpump, but can also be used as a gas com- pressor. The function of a liquid-ring pump is similar to a rotary vane pump, with the differencebeing that thevanes are an integral part of the rotor and churn a rotating ring of liquid to formthe compression-chamber seal. They are an inherently low-friction design, with the rotor being the only moving part. Sliding friction is limited to the shaft seals. Liquid-ring pumps are typically powered by an induction motor. Principle of operation The liquid-ring pump compresses gas by rotating a vaned impeller located eccentri- callywithinacylindricalcasing.Liquid(usually water) is fed into thepump 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, which form compression chambers. The eccentricity between the impeller’s axis of rotation and the casing’s geometric axis results in a cycli- cal 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 cham- bers formed by the impeller vanes and the liquid ring. The reduction in volume caused by the impeller rotation compresses the gas, which reports to thedischargeport in the end of the casing. Sizes and materials available Pumps with a capacity of, as low as 4.0 m³/hr are available and can go up to around 33 000 m³/hr with vacuum ranges fromatmospheric pressure down to vacuum levels of 33 mbar absolute, provided the service liquid temperature is optimal. Motor kWratings from0.075 kWup to 600 kWare

used to drive these units. Cast iron is the most common mate- rial used for the bodies and end plates of the pumps with impeller options in ductile iron, bronze, as well as 304 or 316 stainless steel – and certain manufacturers will also manufacture LRVPs from speciality metals such as Hastelloy. Typically LRVPs are used in power gen- eration equipment, petrochemical, seawater de-aeration, pharmaceutical, ground water remediation/vapour extraction and food production. For more information contact Air & Vacuum Technologies. A large single stage liquid ring vacuum pump for medium and low vacuum, available in South Africa from Air & Vacuum Technologies.

Made with FlippingBook flipbook maker