Lake Monitors Case Drain Monitor - Manual (Page 7)

OPERATION
Operating Principles
Lake has developed a line of unique flow meters which combine the
simplicity of a sharp-edged orifice disk and a variable area flow meter.
See Illustration 1 “Flow Meter Cross Section” on page 8.
The meters are tubular, with all internal wetted parts sealed within
the body casing. Running through the center of the body casing is
a tapered center shaft which is centered in the bore by pilot disks at
each end. Encircling the shaft is a sharp-edged, floating orifice disk,
transfer magnet and return spring. The disk and transfer magnet are
held in the “no flow” position by the biased return spring.
As the flow moves through the meter it creates a pressure differential
across the floating orifice disk, forcing the disk and transfer magnet
against the return spring. As flow increases, the pressure differential
across the disk increases, forcing the disk and transfer magnet to
move along the tapered center shaft. As flow decreases, the biased
return spring forces the disk and transfer magnet down the tapered
center shaft, returning to the “no flow” position.
In metal casing meters we cannot see the movement of the floating
orifice disk and transfer magnet because they are sealed inside the
body casing. Therefore, a magnet follower is positioned around the
outside of the body casing and is magnetically coupled to the internal
transfer magnet. As the flow rate increases, the internal magnet
moves along the tapered center shaft (inside the body casing) and
the magnet follower moves along the outside of the body casing
(under the scale).
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