Design of the Pressure Ports

If the counterpressure at the fixed pressure port is less than the pressure achieved by the volume reduction between the blades, then the compressed medium to be pumped is released via the pressure port. 

The so-called variable pressure ports can be used for the reduction of the restrictor losses. These are generally drillings and slots covered by mobile plates and balls, which open or close depending on the difference of pressure at the valve. The valves are not opened until the pressure, which depends on the angle of rotation and suction pressure in the blade area, is greater than the counterpressure. One can thereby substantially reduce the restrictor losses. 

However, the power requirement of the compression to be made available by the ring fiquid is also reduced by the reduction of the restrictor losses. The fiquid ring is decelerated less, so that the cross section passed through is reduced. Thus, the area available for the gas is enlarged, so that an increase in the suction capacity is to be denoted. 

1 Design and Functional Principle of Liquid Ring Vacuum Pumps I 39 

The arrangement of the valves such that the surface is not covered leads to a pulsating gas discharge. A constant movement of the valves results from this. In comparison to the flaps, the valve bodies are subject to greater wear by the constant impact load. In the case of sufficient decrease in the diameter of the balls, the balls fall through the drillings. The result is a reduction in the suction capacity combined with an increase in the power consumption. 

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For reasons of economy and also for reasons that are historically developed, primary vacuum pumps with inter casings have prevailed in the industry up to now. Deformations of the impeller and inter casing rotationally symmetrical to the shaft centre are conceivable for the enlargement of the working openings. Conical and cylindrical hubs are already completed constructions (Figure 3.7). The possibilities of the medium conveyance discussed in the earlier details as well as the design of the pressure ports are also transferable to the employment of these control bodies. 

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