9
46-620 B73 & Series 75 Liquid Level Switche
s
8. If switch mechanism is operating satisfactorily, proceed to
check sensing unit.
NOTE: As a matter of good practice, spare switches should be kept
on hand at all times.
3.2
Check Sensing Unit
1. Reconnect power supply. Being careful to avoid electrical
shock, manually actuate switch mechanism (use a non-
conductive tool on electrical switch mechanisms) to deter-
mine whether controlled equipment will operate.
Caution:
With electrical power on, care should be taken to avoid
contact with switch leads and connections at terminal
block.
2. If controlled equipment responds to manual actuation test,
trouble may be located in the level sensing portion of the
control, float(s), stem(s), and magnetic attraction sleeve(s).
3. Check to be certain liquid is entering float chamber. A
valve may be closed or piping plugged.
Caution:
Be certain to pull disconnect switch or otherwise ensure
that electrical circuit(s) through control is deactivated.
Close operating medium supply valve on controls
equipped with pneumatic switch mechanisms.
4. With liquid in chamber, proceed to check level sensing
action by removing switch housing assembly and
enclosing tube.
5. Disconnect wiring from supply side of switch
mechanism(s) and remove electrical conduit or operating
medium line connections to switch housing.
6. Perform system shutdown to relieve pressure from float
chamber of control and allow unit to cool.
7. Close shutoff valves (if equipped) to isolate control from
vessel. Drain off liquid in chamber if necessary
8. On installations without shutoff valves, relieve pressure
from vessel and drain off liquid head above control
mounting level.
NOTE: Control chamber, connections, and pipe lines need not be
removed from vessel or boiler.
9. Remove switch housing assembly by loosening hex nut,
which is located immediately below housing base.
10. With switch housing assembly removed, inspect attraction
sleeve(s) and inside of enclosing tube for excessive corro-
sion or solids buildup which could restrict movement, pre-
venting sleeve(s) from reaching field of switch magnet(s).
