The compressor is driven by a variable speed d.c. electric motor with a belt gearing-up system of O to 4000 RPM with a transmission ratio of 7.5/1.If is possible to read the pressure values, upstream and downstream of the compressor, by means of 2 U shaped differential manometers. The industrial type compressor used in this apparatus is a single stage machine having a 127 mm dia impeller and an aluminium scroll with fluid threads rectifier. Thermometers are inserted into the circuit in order to read the air temperature before and after the passage through the centrifugal compressor. At the maximum speed of over 29,000 RPM, if develops a downstream pressure of about 230 mmHg with a max air capacity of 1230 kg/h.
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