JZJS roots vacuum unit is made up of the series connected roots pump and water ring pump, where the roots pump is the main pump and the water ring pump is used as the fore pump. It is more efficient for the roots water ring vacuum unit to select a water ring vacuum pump as the fore pump, which overcomes the ultimate pressure difference when using a single water ring pump (compared with the water ring pump, the ultimate pressure of the unit is great improved), and the low pumping rate under a certain pressure, while retaining the fast work and higher pumping rate of the roots pump. In particular, it is adapt to pump a great amount of condensable vapors, and it is more obvious when the capacity of the gas ballast oil sealed mechanical vacuum pump is insufficient to pump condensable vapors, or the applied solvents deteriorate the pump oil to influence performances, or the vacuum system does not allow oil pollution. When equipped with an explosion-proof electric motor and in compliance with appropriate safety regulations, it can be also used to pump flammable and explosive gases. Therefore roots pump – water ring pump unit is widely used for the vacuum distillation, vacuum evaporation, dehydration and crystallization in the chemical industry; freeze drying in the food industry; the vacuum drying in the pharmaceutical industry; the terylene section cutting in the light textile industry; the vacuumizing system in high-altitude simulation test, and so on.
Roots water ring vacuum units generally include the following types:
(1) Roots pump-water ring pump: The water ring pump in this unit is used to produce the fore vacuum required for the roots pump. In general, the ultimate vacuum degree of the single-stage water ring vacuum pump is not high, and at present, the roots pumps made in China require higher ultimate vacuum degree, thus, in fact, the single-stage water ring pump is not usually used as the fore pump of the roots pump. The two-stage water ring pump with lower ultimate pressure can be applied as the fore pump, or reduce the ultimate pressure of the unit.
The ultimate pressure of one roots pump and one water ring pump is 400Pa, which can meet the general needs of vacuum, but the range of use is subject to certain restrictions. If combine two series connected roots pumps and the water ring pump, the ultimate pressure can be greatly increased (up to 25Pa). Therefore, for this type, the combination of two series connected roots pumps with a twostage pump as the pore pump (Figure 1) is common to compose the unit. If need a higher ultimate pressure, a combination of three roots pumps with a water ring pump can be used, whose ultimate pressure can be up to t 1Pa.
(2) If the three-stage roots water ring unit can not meet the ultimate pressure, the roots pump-water ring pump parallel mechanical vacuum pump can be adopted; this unit is mainly for a vacuumizing system which is used to treat a great amount of water vapor, and requires a long time and a very high ultimate vacuum degree, e.g, in the vacuum drying area.
In the vacuum system which is used to treat a great amount of water vapor, water ring pump is more appropriate choice. However, its ultimate vacuum degree is not high, as a result, the ultimate vacuum degree of the entire unit is lower (relatively).
Although in the vacuumizing system requiring higher vacuum degree, the mechanical vacuum pump of higher ultimate vacuum shall be used as the fore pump, the gas ballast mechanical vacuum pump and water-ring pump can be connected in series to act as the fore pump of the roots pump (see Figure 2). In vacuum drying, first use the water ring pump for forepumping until there is a significant reduction in water vapor, and then switch on the gas ballast mechanical vacuum pump, and switch off the water ring pump. If it takes longer time to complete drying, the required cooling water and power is less as shown in Figure 2.