Replacement Head Mechanism
!
Snap Switch
Models:
150S-HD
150S-M-HD
150S-MD-HD
150S-M-MD-HD
158S-HD
158S-M-HD
158S-MD-HD
158S-M-MD-HD
159S-HD
Replacement head mechanisms can be installed without
disturbing existing equalizing connections or disassembly
of components, making repair simple and easy.
INSTRUCTION MANUAL
MM-219J
Replacement Head Mechanism
WARNING
N
UTIO
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.
Failure to follow this warning could cause property damage, personal injury or death.
2
Enclosure rating: NEMA 1 General Purpose
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
15
/16 (24)
5
/16 (8)
Pump On
5
/8 (16)
Burner On
5
/8 (16)
3
/8 (16)
Burner Off
1
/4 (6.4)
Pump Off 13/8 (41)
3
/4 (19)
Pump On
5
/8 (16)
Burner On
7
/8 (22)
7
/8 (22)
Burner Off 0 (0)
BURNER OFF
BURNER ON
7
/8"
DIFFERENTIAL
(22mm)
PUMP
OFF
BURNER
OFF
NORMAL BOILER
WATER LINE
1
3
/8"
DIFFERENTIAL
(35mm)
PUMP OFF
PUMP ON
3
/4"
DIFFERENTIAL
(19mm)
PUMP OFF
PUMP ON
3
/4"
DIFFERENTIAL
(19mm)
PUMP
OFF
BURNER
OFF
NORMAL BOILER
WATER LINE
1
13
/16"
DIFFERENTIAL
(46mm)
OPERATION
Maximum Pressure: 150 psi (10.5 kg/cm2)
Electrical Ratings
Settings and Differential Pressures
Values are ± 8" (3.2mm).
Series 150S and 157S
150 psi (10.5 kg/cm
2
) Levels
150 psi (10.5 kg/cm
2
) Levels
0 psi
(0 kg/
cm2)
150 psi
(10.5 kg/
cm
2
)
Approximate
Distance Above
Cast Line Differential
Setting In. (mm) In. (mm)
Pump Off
15
/16 (24)
3
/8(16)
Pump On
9
/16 (14)
Burner Off 0 (0) N/A
Pump Off 17/16 (37)
3
/4(19)
Pump On 11/16 (17)
Burner Off - 3/8 (-16)
N/A
Model 150S-MD and 157S-MD
0 psi
(0 kg/
cm
2
)
150 psi
(10.5 kg/
cm
2
)
Pressure
Pressure
Alarm Circuit Rating
Voltage Amps
120 VAC 1
240 VAC 1/2
Motor Horsepower
Voltage Hp
120 VAC
1/3
240 VAC 1/3
3
Approximate
Distance Above
Cast Line Differential
Setting In. (mm) In. (mm)
Motorized
15
/16 (24)
Valve Closed
5
/16 (8)
Motorized
5
/8 (16)
Valve Open
Burner On
5
/8 (16)
3
/8(16)
Burner Off
1
/4 (6.4)
Motorized 13/8 (41)
3
/4 (19)
Valve Closed
Motorized
5
/8 (16)
Valve Open
Burner On
7
/8 (22)
7
/8(22)
Burner Off 0 (0)
BURNER OFF
BURNER ON
7
/8"
DIFFERENTIAL
(22mm)
MOTORIZED
VALV E
CLOSED
BURNER
OFF
NORMAL BOILER
WATER LINE
1
3
/8"
DIFFERENTIAL
(35mm)
MOTORIZED
VALV E
CLOSED
MOTORIZED
VALV E
OPEN
3
/4"
DIFFERENTIAL
(19mm)
Values are ± 8" (3.2mm).
NOTE: Due to the slower operation of some
motorized valves, complete valve opening
or closing will occur at slightly different
levels than indicated above.
Model 158S
150 psi (10.5 kg/cm
2
) Levels
0 psi
(0 kg/
cm
2
)
150 psi
(10.5 kg/
cm
2
)
Pressure
Settings and Differential Pressures (continued)
150 psi
(10.5 kg/
cm
2
)
MOTORIZED
VALVE
OPEN
CLOSED
3
/4"
DIFFERENTIAL
(19mm)
MOTORIZED
VALV E
CLOSED
BURNER
OFF
NORMAL BOILER
WATER LINE
1
13
/16"
DIFFERENTIAL
(46mm)
Approximate
Distance Above
Cast Line Differential
Setting In. (mm) In. (mm)
Pump Off
15
/16 (24)
3
/8(16)
Pump On
9
/16 (14)
Burner Off 0 (0) N/A
Pump Off 17/16 (37)
3
/4(19)
Pump On 11/16 (17)
Burner Off - 3/8 (-16)
N/A
Model 158S-MD
0 psi
(0 kg/
cm
2
)
Pressure
150 psi (10.5 kg/cm2) Levels
NOTE: Due to the slower operation of some
motorized valves, complete valve opening
or closing will occur at slightly different
levels than indicated above.
4
PUMP #1
OFF
PUMP #1
ON
NORMAL BOILER
WATER LINE
(19mm)
3
/4"
DIFFERENTIAL
PUMP #2 ON
AT CAST LINE
7
/8"
DIFFERENTIAL
(22mm)
PUMP #2
ON
PUMP #2
OFF
PUMP #1
OFF
PUMP #2
ON
PUMP #2 ON
AT CAST LINE
NORMAL BOILER
WATER LINE
1
3
/8"
DIFFERENTIAL
(35mm)
Values are ± 8" (3.2mm).
150 psi (10.5 kg/cm2) Levels
Approximate
Distance Above
Cast Line Differential
Setting In. (mm) In. (mm)
Pump #1 Off15/16 (24)
5
/16(8)
Pump #1 On5/8 (16)
Pump #2 Off5/8 (16)
3
/8(16)
Pump #2 On1/4 (6.4)
Pump #1 Off 13/8 (41)
3
/4(19)
Pump #1 On5/8 (16)
Pump #2 Off7/8 (22)
7
/8(22)
Pump #2 On
0 (0)
Model 159S
0 psi
(0 kg/
cm
2
)
150 psi
(10.5 kg/
cm
2
)
Pressure
Settings and Differential Pressures (continued)
• 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 disconnecting or making electrical connections.
Failure to follow this warning could cause property damage, personal injury or death.
!
WARNING
5
A
B
C
D
c. Remove the existing head mechanism (C)
from the body (D).
a. Drain water in the boiler to a level which is
below the float chamber (A). Allow the boiler
to cool to 80˚F (27˚C) and release the boiler
pressure to 0 psi (0 bar).
b. Using a flathead screwdriver, remove the junction
box cover (B). Disconnect, mark, and remove the
supply wires and conduit connections.
F
E
d. Using a scraper, remove the old gasket (E).
Clean all debris from the float chamber. The
gasket sealing surface (F) must be smooth
and clean.
STEP 1 - Preparation
INSTALLATION
TOOLS NEEDED:
One (1) pipe wrench, one (1) flathead screwdriver, one (1) scraper, and one (1) 9/16" socket or wrench.
There may be more than one source of power to the boiler.
!
CAUTION
d. Using a wrench, insert the eight (8) bolts and
tighten them to approximately 14-20 ft•lb
(19-27 N•m) in an alternating star pattern.
G
J
b. Align the bolt holes of the new head gasket (J)
on the sealing surface of the control body.
a. Carefully remove the new replacement head
mechanism from the carton. Handle it carefully
to prevent damage to the float rod (G).
K
D
c. Install the new replacement head (K) on the
body (D) by guiding the float into the control
body and aligning the bolt holes.
STEP 2 - Installing the Replacement Head Mechanism
6
7
IMPORTANT: There must be a
minimum space of 1/2" (13mm)
between connector fittings and
electrical live metal parts.
STEP 3 - Electrical Wiring
a. Reconnect conduit and wires which were disconnected prior to head removal.
b. Re-attach the junction box cover (B).
B
Note:
Cover must be installed correctly as shown
• To prevent a fire, do not use this product 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.
• 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.
• Modification of the switch assembly before or after installation could cause damage to the boiler and/or
boiler system.
Failure to follow this warning could cause electrical shock, an explosion and/or a fire, which could result in
property damage, personal injury or death.
!
WARNING
8
Switch Operation
For all Models except 158S and 159S
For Model 158S
Boiler feed pump off,
burner on, alarm off.
Boiler feed pump on,
burner on, alarm off.
Boiler feed pump on,
burner off, alarm on.
Motorized valve closed,
burner on, alarm off.
Motorized valve open,
burner on, alarm off.
Motorized valve open,
burner off, alarm on.
4 5 6
1 2
3
4 5
1 2
3
4 5
1 2
3
6 6
For Model 159S
Pump #1 off,
pump #2 off.
Pump #1 on,
pump #2 off.
Pump #1 on,
pump #2 on.
1 2 5 6 1 2 5 6
1 2 5 6
1 2 4 5 6 1 2 4 5 6
1 2 4 5 6
9
WIRING DIAGRAMS
For Motorized Valves, refer to the valve manufacturer's wiring instructions.
Pump Control Only
1. Install a starter or relay in pump control circuit,
as shown, to prevent damage to snap switch
and help insure proper switch/control operation.
Failure to do so may shorten the life of the switch
when actual amperage exceeds switch rating.
2. Connect wires from holding coil of pump starter
or relay to terminals 1 and 2 as shown.
1. Main Line Switch - For burner circuits within
the switch’s electrical rating.
2. Pilot Switch - To holding coil of a starter when
the burner circuit exceeds the switch’s electrical
rating.
12 456
ALARM
NEUTRAL
HOT
ALARM
NEUTRAL
HOT
12 4 56
12 456
SEE PUMP
CONTROL
CIRCUIT
TO NEUTRAL
TO BURNER CONTROL CIRCUIT
HOT
ALARM
12 456
LOAD
LINE (3 PHASE)
SEE PUMP
CONTROL
CIRCUIT
ALARM
OR
OR
Combination Pump Control, Low Water Cut-Off and Alarm
Alarm Circuit Only
1. Low Water Alarm 2. High Water Alarm
NOTE
To help insure most effective operation,
balance boiler feed pump(s) to deliver
required water feed rate to match boiler
steaming requirements.
NOTE
For Model 159S, use terminals 5 and 6 from
starter or relay for pump #2.
Low Water Cut-Off Only
1. Main Line Switch - For burner circuits within the
switch’s electrical rating.
LINE LOAD
12 456
12 456
LOAD
LINE
OR
2. Pilot Switch - To holding coil of a starter when
the burner circuit exceeds the switch’s electrical
rating.
LINE
12 456
LOAD
K
To prevent serious personal injury from steam pipe blow
down, connect a drain pipe to the control opening to
avoid exposure to steam discharge.
Failure to follow this caution could cause personal injury.
!
CAUTION
INSTALLATION COMPLETE
10
Snap Switch Models
STEP 4 - Testing
OFF
ON
a. Turn on the electric power to the boiler.The pump should go on
and the burner must remain off.
IMPORTANT: Follow the boiler manufacturer’s start-up and operating instructions along with all applicable codes and ordinances.
This control is factory calibrated for specific level
settings as shown on pages 2-4 in the “Operation”
section.
The following testing procedure is only meant to
serve as a verification of proper operating
sequence.
If the burner comes on, immediately turn the boiler off and make the
necessary corrections.
Failure to follow this warning could cause an explosion or fire and
result in property damage, personal injury or death.
!
WARNING
b.
The boiler should begin to fill with water.
As the water level rises in the sight glass,
the burner should turn on and then the
pump should turn off at appropriate levels.
For manual reset models, press the reset
button (K) when the water reaches appropriate level.
If the burner does not turn on or pump
turn off at appropriate levels, immediately
turn off the boiler and make necessary
corrections.
Location of Manual Reset Button
c.
Blow down the control when the water in the boiler is at
its normal level and the burner is on. Follow Blow Down
Procedure found in Maintenance Section on page 11 of
these instructions.
11
MAINTENANCE
SCHEDULE:
Blow down control as follows when boiler is
in operation.
• Daily if operating pressure is above 15 psi.
• Weekly if operating pressure is below 15 psi.
• Remove head assembly and inspect water
side components annually. Replace head
assembly if any of the internal components are
worn, corroded or damaged or if control no longer
operates properly.
• Inspect the float chamber and equalizing piping
annually. Remove all sediment and debris.
Replace head mechanism every 5 years.
More frequent replacement may be required when
severe conditions exist.
Replacement parts are available from your local
authorized McDonnell & Miller Distributor.
The use of parts or components other than those
manufactured by McDonnell & Miller will void all
warranties and may affect the units compliance with
listings or regulating agencies.
BLOW DOWN PROCEDURE:
When blowing down a control at pressure, the blow
down valves should be opened slowly. The piping
needs to be warmed up and stagnant water in the
drain piping needs to be pushed out. Suddenly
opening a blow down valve causes steam to
condense, which can create water hammer.
Damage to components can occur when water
hammer occurs due to improper blow down piping.
For these reasons, McDonnell & Miller recommends
a dual valve blow-down system for each control.
Blow down the control when the water in the boiler
is at its normal level and the burner is on.
NOTE: Refer to page 2 for switch operating points.
• Open upper valve (#1)
• Slowly open the lower valve (#2)
• Water in the sight glass should lower.
• As the water in the sight glass lowers, the
pump should turn on.
• As the water continues to lower in the sight
glass, the burner should turn off.
• Slowly close the lower valve (#2).
• Close the upper valve (#1)
• The water level in the sight glass should rise, first
turning on the burner and then turning off the pump.
NOTE: On manual reset models, the reset button
will need to be pressed after the water level has
been restored before the burner will operate.
To prevent serious personal injury from steam
pipe blow down, connect a drain pipe to the
control opening to avoid exposure to steam
discharge.
Failure to follow this caution could cause
personal injury.
!
CAUTION
NOTE
More frequent blow-down may be necessary
due to dirty boiler water and/or local codes.
NOTE
The control may need to be inspected and
cleaned more frequently on systems where there
is the potential of excessive scale or sludge
build-up. This includes systems:
• With high raw water make-up
• With no condensate return
• With untreated boiler water
• Where significant changes have been
made to the boiler-water chemical
treatment process
• With oil in the boiler water
NOTE
If this sequence of operation does not occur as
described, immediately close all the valves, turn off the
boiler and correct the problem. Inspection/cleaning of
the float mechanism may be required to determine why
the control was not working properly. Retest the control
after the problem has been identified and corrected.
Valve #1
Valve #2
Xylem
1) The tissue in plants that brings water upward from the roots;
2) a leading global water technology company.
We’re 12,500 people unified in a common purpose: creating innovative solutions
to meet our world’s water needs. Developing new technologies that will improve
the way water is used, conserved, and re-used in the future is central to our work.
We move, treat, analyze, and return water to the environment, and we help people
use water efficiently, in their homes, buildings, factories and farms. In more than
150 countries, we have strong, long-standing relationships with customers who
know us for our powerful combination of leading product brands and applications
expertise, backed by a legacy of innovation.
For more information on how Xylem can help you, go to www.xyleminc.com
Xylem Inc.
8200 N. Austin Avenue
Morton Grove, Illinois 60053
Phone: (847) 966-3700
Fax: (847) 965-8379
www.xyleminc.com/brands/mcdonnellmiller
McDonnell & Miller is a trademark of Xylem Inc. or one of its subsidiaries.
© 2012 Xylem Inc. MM-219J August 2012 Part No. 210343
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