Xylem MM 251C Series 750B-C3 Chamber with 3 Probes Series 750B-C4 Chamber with 4 Probes - Manual (Page 3)

CUT-OFF
LEVEL
Pump Off
Pump On
Burner Off
LOWER
EQUALIZING
LINE
2-5/16" (6mm)
Chamber
3
IMPORTANT: Do not use PTFE tape or hardening type
thread sealant. Use of pipe dope or hi-temp boiler grease
is recommended.
If the control will be the primary low water fuel
cut-off, size the steam (top) and water (bottom)
equalizing pipe lengths so that the cut-off level
mark is 1
1 /
2
” (38mm) below the boiler’s normal
water level, but not lower than the lowest safe
permissible water level, as determined by the
boiler manufacturer.
OR
If the control will be the secondary low water
fuel cut-off, size the steam (top) and water (bottom)
equalizing pipe lengths so that the cut-off level
mark is at or above the lowest safe permissible
water level, as determined by the boiler
manufacturer.
Probes and Electrical Connections
• Each probe is made up of an electrode and a probe rod. Each
probe rod must be cut to an appropriate point of operation.
• A 9" rod will be positioned at the low water cut-off level.
Cut other rods for the pump operating probes to the desired
length.
• After cutting, secure the probe rod to the electrode and lock
the thread using the jamnut in the electrode sleeve. Insert the
probe into the chamber and tighten by hand. Then torque to
22-25 ft/lbs (30-34 N/m).
• Refer to and follow all local codes and standards.
• Secure the electrical enclosure to the chamber with gasket
between. Note that the electrical connection opening can be
orientated in any of 4 positions. Tighten screws to 30 - 35 in/lbs
(3.4-4.0 N/m).
• Probe wire and conduit connections should be made following
accepted electrical practices.
• Install electrical cover enclosure after making all connections
and after control has been tested for proper operation.
Tighten screws to 30 - 35 in/lbs (3.4-4.0 N/m).
Wire must be 18 AWG stranded with glass braided silicone jacket
(UL 3071) suitable for high temperature (200˚C) service.
NOTE