Water meters to be mounted in the pipe conduits of a nominal diameter class and method for operating such water meters

A water meter for the installation in pipe lines of a nominal width-group with successive nominal width, said water meter comprising:

• a housing having an aligned inflow region and outflow region;
• a measuring insert disposed coaxially between said regions, said measuring insert is identical for all nominal widths of the nominal width-group;
• said measuring insert comprises a measuring annulus;
• a coaxially disposed upstream and downstream holding means;
• an impeller wheel rotatably supported between said holding means;
• said impeller wheel having vanes which project into an annular channel formed between the holding means and the measuring annulus;
• characterized in that the inner contour of the inflow region and the outer contour of the upstream holding means are developed such that, independently of the nominal width of the connected pipe line, in the annular channel directly in front of the impeller wheel a substantially rectangular velocity distribution obtains with stream lines directed substantially parallel to the wall of the annular channel;
• wherein the upstream holding means comprises a substantially perpendicular face toward a stream incidence, which transitions into a cylindrical or slightly conically diverging shell surface having substantially parallel walls forming an inner wall of the annular channel;
• and
• wherein only a single calibration is needed for use in any member pipe of the nominal width-group.