Richter's vent adapter is a special duct fitting from a sheet metal, installed before of industrial fan. Gases or air are supplied through the inlet Richter's adapter to the suction pipe of draft blowers (industrial fans).
Their parts are designed on the basis of USSR standards: PGVU 022-81, PGVU 023-81. Here is the complicated part in the calculations in the manufacture of the Richter's adapter (the visor).

Unfolded curved surface of the visor of the Richter's vent adapter.
It is cut out on sheet metal with further circular rolling.

Richter's vent fitting
Tilt angle (L) of visor
°
Visor height (h)
mm
Visor base radius (r)
mm
Number (n) of split points
point
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