While the blower is in normal operation, i.e. after start-up, the main valve disc is closed and the pressure in
the control valve is on both sides of its cone (small ball). The force generated by pressure against the
membrane, the surface of which is larger than the surface of the small ball contacting in the seat, is smaller
than the total forces generated by the spring and by pressure against the small ball surface in the seat. The
control valve is closed