a bottom part of the housing 8a while its other end engages the metal support plate 12 a clearance 15 is provided between an end 14a of the electronic proximity switch 14 and the metal plate 12 the clearance 15 is adjustable by changing the axial position of the proximity switch 14 by virtue of its threaded connection with the housing 8a the other opposite end of the electronic proximity switch 14 is connected with the regulator 9 fig1 by means of a conductor 16 the electronic pressure responsive switch 8 is adapted to measure the pressure prevailing in the feeding shaft 4 in a range from 0 to 150 mm ws pressure fluctuations in this range are converted by the electronic proximity switch 14 into the continuous analog signal x as a function of the pressure dependent distance of the metal plate 12 from the end 14a of the electronic proximity switch 14 in the range between 50 and 150 mm ws the output signal x of the electronic proximity switch 14 is linearly proportionate to the pressure in the feeding shaft 4 fig3 a is an elevational view and fig3 b is a plan view of a tuft feeding installation a transport blower 17 has its suction side connected to a fine opener 18.