Roots blower

Roots Blowers The term “Roots” vacuum pump derives from the Roots brothers who invented the rotary lobe pump more than a century ago. Still in business today, Roots™ vacuum pumps are a diverse line of pumps manufactured by Roots division of industrial giant Dresser Industries. In general usage however, the name “roots blower” usually refers to a specific design of vane pump, the “liquid ring pump” or “water sealed vacuum pump”.

Liquid ring vacuum pumps are electromechanical pumps that achieve moderate levels of vacuum pressure and high volume of vacuum flow, and will tolerate very harsh applications. Liquid ring pumps can be applied in wet industrial environments and, as they are inherently low in friction, the user may expect a long service life.

The liquid ring pump removes air or gases by means of an impeller rotating freely in an eccentric casing. Liquid, usually water, is fed into the pump and is thrown by centrifugal force to form a moving ring along the internal casing wall, creating a sealed pumping chamber. The eccentric mounting of the impeller with respect to the casing results in increased spacing between the impeller blades at the inlet port and decreased spacing near the outlet port. Gas or air drawn into the pump via the impeller is trapped in the space and is compressed as it nears the outlet. The vanes, typically powered by electric motor, continuously enter and leave this ring of liquid. The vanes eject the sealant water from the gaps between the vanes, while drawing air or gasses through the inlet. At the outlet, the ejected sealant liquid is separated for recycling.

Typical liquid ring systems are single stage pumps but they can also be joined in multiple pumping stages to reduce the pressure further. Industrial users employ these somewhat low tech but highly reliable pumps for a variety of uses, such as forming wet paper pulp into egg cartons and nursery planting containers, soil remediation where contaminated ground water is drawn by vacuum from the earth for treatment, and a host of other applications. They are not only used in vacuum technology, but also as chargers for engines.

Single stage pumps typically produce less than 29”Hg vacuum, assuming air is being pumped and water is the sealing media. The small gap between the rotor and the housing needs no lubrication (apart from the bearings). They are available with or without bypass valve to avoid overheating of the internal rotors. Greater vacuum pressures are obtainable by using oil or other sealants, or by adding booster pumps.

There are many variables that must be considered in designing a liquid ring vacuum system. Factors such as vapor pressure and temperature, limitations of the sealant, condensing rates of the pumped vapor within the pump, cavitation, corrosion, elastomer compatibility, sealant recovery methods and many other factors must be scrutinized.

Availability of water for sealing can be problematic. Municipal water sources can be cost-prohibitive, however well water or other natural resources may be available. Some liquid ring pump users construct water cooling towers. Hot waste water can be pumped to an overhead holding tank and then showered down via gravity to cool and be collected for re-use.

Still, sealant water ultimately becomes mixed with lubricants, additives and contaminants that may be drawn into the inlet, thus the cleaning and ultimate disposal of wastewater or other sealant adds to the cost of operating the system.

Alternative pump designs are numerous. When evaluating the ultimate cost of using liquid ring pumps, the ongoing cost of acquiring and disposing of sealant must be factored in. The modest initial price tag on the pump is one factor. However, operating and maintenance expenses over the life of the pump may justify a different design of pump with higher initial cost, but which may be less costly to operate in the long run.

External link

• www.vacuum-guide.com (http://www.vacuum-guide.com/firmenlisten/produkte/roots_vacuum_blower_america.htm) - Roots blowers manufacturer directory