Magnetrol C75 - High Level Controls; Tandem Float Models; Installation, Preventive Maintenance; And Troubleshooting

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46-620 B73 & Series 75 Liquid Level Switches
2.4.2 High Level Controls
On high level controls, the switch trips on the higher actu-
ation point and resets on the lower actuation point.
Caution: On high level controls, widening the differential requires
raising the trip point a proportional amount. The reset
point will remain the same.
To widen the differential by raising the trip point, follow
steps 1 through 16 in
Section 2.4.1, Low Level Controls
on pages 5–6.
2.5
Tandem Float Models
Models with tandem floats are used on applications where
it is advantageous to have two widely spaced high and low
switching functions using a single control.
The units incorporate two floats which operate independ-
ently, and are arranged so that the lower float actuates the
upper switch mechanism, and the upper float actuates the
lower switch mechanism. The upper float is attached to
the lower attraction sleeve by means of a hollow stem. The
lower float attaches to the upper attraction sleeve with a
solid stem that extends upward through the upper float
and stem assembly.
2.5.1 Installation, Preventive Maintenance, and
Troubleshooting
Installation and maintenance of tandem float models is
accomplished in much the same manner as for standard
models previously described. Some additional considera-
tion must be given to the piping arrangement to allow for
alignment of the two switch actuating level marks on the
float chamber with the desired levels in the vessel. When
troubleshooting the level sensing portion of the control,
additional checks may be made of the following:
1. Inspect for binding of solid (lower) float stem within hol-
low (upper) float stem due to corrosion or possible damage
incurred during shipment or previous maintenance.
2. Make certain that retaining (snap) rings, used to locate
lower attraction sleeve, are locked in place. An extreme
shock or hammer, such as during blow-down on a water
column boiler control, may damage a ring causing it to
snap out of its retaining groove in the hollow (upper)
float stem.