Xylem MM 231F User Manual
Series 42S
(Snap Switch)
Low Water Cut-Off/Pump Controller
For Steam Boilers
Typical Applications:
– Pump controller/low water fuel cut-off
for steam boilers
– Low water cut-off
INSTRUCTION MANUAL
Series 42S-A
MM-231F
Series 42S
Series 42S-N
WARNING
!
N
TIO
U
A
C
G
NIN
R
A
W
• Before using this product read and understand instructions.
• Save these instructions for future reference
• All work must be performed by qualified personnel trained in the proper application, installation, and maintenance of plumbing, steam, and electrical equipment and/or systems in
accordance with all applicable codes and ordinances.
• To prevent serious burns, the boiler must be cooled to 80˚F (27˚C) and the pressure must be
0 psi (0 bar) before servicing.
• To prevent electrical shock, turn off the electrical power before making electrical connections.
• This low water cut-off must be installed in series with all other limit and operating controls
installed on the boiler. After installation, check for proper operation of all of the limit and
operating controls, before leaving the site.
• We recommend that secondary (redundant) low water cut-off controls be installed on all
steam boilers with heat input greater than 400,000 BTU/hour or operating above 15 psi of
steam pressure. At least two controls should be connected in series with the burner control
circuit to provide safety redundancy protection should the boiler experience a low-water
condition. Moreover, at each annual outage, the low water cut-offs should be dismantled,
inspected, cleaned, and checked for proper calibration and performance.
• To prevent serious personal injury from steam blow down, connect a drain pipe to the control
opening to avoid exposure to steam discharge.
• To prevent a fire, do not use this low water cut-off to switch currents over 7.4A, 1/3 Hp at
120 VAC or 3.7A, 1/3 Hp at 240 VAC, unless a starter or relay is used in conjunction with it.
California Proposition 65 warning! This product contains chemicals known to the
•
!
state of California to cause cancer and birth defects or other reproductive harm.
Previous controls should never be installed on a new system. Always install new
•
controls on a new boiler or system.
Failure to follow this warning could cause property damage, personal inj ury or death.
Pump Circuit Rating (Amperes)
Voltage Full Load Locked Rotor Pilot Duty
120 VAC 7.4 44.4
345 VA at
240 VAC 3.7 22.2
120 or 240 VAC
Approximate
Distance Above
Cast Line Differential
Setting In. (mm) In. (mm)
Pump Off 13/8(35)
3
/4(19)
Pump On
5
/8(16)
Burner On
7
/8(22)
7
/8(22)
Burner Off 0 (0)
NORMAL BOILER
WATER LINE
BURNER
CUT-OFF LEVEL
AT CAST LINE
7/8" (22 mm)
BURNER ON
BURNER OFF
CUT-OFF
LEVEL
NORMAL BOILER
WATER LINE
PUMP
OFF
BURNER
OFF
BURNER
CUT-OFF LEVEL
AT CAST LINE
1 3/8" (35mm)
CUT-OFF
LEVEL
NORMAL BOILER
WATER LINE
CUT-OFF
LEVEL
PUMP OFF
PUMP ON
3/4" (19mm)
OPERATION
Maximum Pressure: 50 psi (3.5 kg/cm2)
Electrical Ratings
Settings and Differential Pressures
Values are ± 8” (3.2mm).
Series 42S
50 psi
(3.5 kg/
cm2)
Pressure
2
Motor Horsepower
Voltage Hp
120 VAC
1/3
240 VAC 1/3
CAUTION:
•
A more frequent replacement interval may be necessary based on the condition of
the unit at time of inspection. McDonnell Miller s warranty is one (1) year from date
of installation or two (2) years from the date of manufacture.
&
'
3
1"
The 42S and 42S-N controls are
installed so that the horizontal cast line
on the body is 1aa” (35mm) below the
boiler’s normal water level, but not
lower than the lowest, safe permissible water level, as determined by the
boiler manufacturer.
The 42S-A controls are installed in boiler’s gauge glass tappings. The horizontal
cast line should be approximately 1” (25
mm) above the bottom of the glass.
Verify that this level is not below the
lowest, safe permissible water level,
as determined by the boiler manufacturer.
STEP 1 - Determine the Elevation at Which the
Low Water Cut-Off/Pump Controller Must be Installed
INSTALLATION –
TOOLS NEEDED:
Two (2) pipe wrenches, one (1) flathead screw
driver, and pipe sealing compound.
IMPORTANT: Follow the boiler manufacturer's
instructions along with all applicable codes and
ordinances for piping, blow down valve and water
gauge glass requirements.
13/8"
STEAM EQUALIZING PIPE
VERTICAL EQUALIZING PIPE
BLOW DOWN VALVE
NORMAL BOILER
WATER LINE
LOW WATER
CUT-OFF/PUMP CONTROLLER
BURNER CUT-OFF
LEVEL AT CAST LINE
LOWEST
PERMISSIBLE
WATER LEVEL
(35mm)
WATER
EQUALIZING
PIPE
STEAM EQUALIZING PIPE
VERTICAL EQUALIZING PIPE
BLOW DOWN VALVE
LOW WATER
CUT-OFF/PUMP CONTROLLER
BURNER CUT-OFF
LEVEL AT CAST LINE
WATER
EQUALIZING
PIPE
13/8"
NORMAL BOILER
WATER LINE
LOWEST
PERMISSIBLE
WATER LEVEL
(35mm)
Series 42S
Series 42S-N
4
For 42S-A Control
H
INVERTED “Y” CASTING
Note:
Reverse union
nuts, packing
and plug.
Tighten top
nut securely.
J
H
G
F
J
c. Determine the position of the black ‘Y’ casting (H).
If gauge glass tappings (F) and (G) are less
than 10
5
⁄8" (270 mm) apart, install the black
‘Y’ casting (H) as depicted in the diagram to the
top right.
OR
If gauge glass tappings (F) and (G) are
greater than 10
5
⁄8" (270 mm) apart, invert
the black ‘Y’ casting (H) as depicted in the
diagram to the bottom right.
OR
If gauge glass tappings (F) and (G) are
greater than 14" (356 mm) apart, invert the
black ‘Y’ casting (H) as depicted in the diagram
to the bottom right and install a longer brass nipple (J).
C
a. Drain the water in the boiler until the level falls below the lower
gauge glass connection (C). Allow the boiler to cool to 80˚F
(27 ˚C) and allow the pressure to release to 0 psi (0 bar).
D
E
b. Remove the water glass (D) and gauge glass connections (E)
from the boiler.
STEP 2 - Installation
B
A
a. Using a pipe wrench, unscrew shipping block (A) from
upper 1” NPT tapping (B) of the control body.
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