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Replacement Head Mechanism
Snap Switch
Models:
Replacement head mechanisms can be installed without
disturbing existing equalizing connections or disassembly
of components, making repair simple and easy.
• 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, instal-
lation, 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.
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
®
!
WARNING
McDonnell & Miller
Installation & Maintenance
Instructions
MM-219(I)
Replacement Head Mechanism
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Table of Contents
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Summary of Contents for ITT 150S-HD
- Page 1 McDonnell & Miller Installation & Maintenance Instructions MM-219(I) 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 Mechanism Replacement head mechanisms can be installed without disturbing existing equalizing connections or disassembly of components, making repair simple and easy.
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Page 2: Operation
OPERATION Maximum Pressure: 150 psi (10.5 kg/cm Electrical Ratings Alarm Circuit Rating Motor Horsepower Pump Circuit Rating (Amperes) Voltage Amps Voltage Voltage Full Load Locked Rotor Pilot Duty 120 VAC 120 VAC 120 VAC 44.4 345 VA at 120 or 240 VAC 240 VAC 22.2 240 VAC... - Page 3 Settings and Differential Pressures (continued) Values are ± 8" (3.2mm). Model 158S Model 158S-MD Approximate Approximate Distance Above Distance Above Cast Line Differential Cast Line Differential Setting In. (mm) In. (mm) Pressure Pressure Setting In. (mm) In. (mm) Motorized (24) Pump Off (24) 0 psi...
- Page 4 Settings and Differential Pressures (continued) Values are ± 8" (3.2mm). Model 159S Approximate Distance Above Cast Line Differential Setting In. (mm) In. (mm) Pressure Pump #1 Off (24) 0 psi Pump #1 On (16) (0 kg/ Pump #2 Off (16) (16) Pump #2 On (6.4)
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Page 5: Installation
INSTALLATION TOOLS NEEDED: One (1) pipe wrench, one (1) flathead screwdriver, one (1) scraper, and one (1) 9/16" socket or wrench. STEP 1 - Preparation WARNING • 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. - Page 6 STEP 2 - Installing the Replacement Head Mechanism a. Carefully remove the new replacement head mechanism from the carton. Handle it carefully to prevent damage to the float rod (G). b. Align the bolt holes of the new head gasket (J) on the sealing surface of the control body.
- Page 7 STEP 3 - Electrical Wiring WARNING • 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. •...
- Page 8 Switch Operation For all Models except 158S and 159S Boiler feed pump off, Boiler feed pump on, Boiler feed pump on, burner on, alarm off. burner on, alarm off. burner off, alarm on. For Model 158S Motorized valve closed, Motorized valve open, Motorized valve open, burner on, alarm off.
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Page 9: Wiring Diagrams
WIRING DIAGRAMS For Motorized Valves, refer to the valve manufacturer's wiring instructions. Low Water Cut-Off Only 1. Main Line Switch - For burner circuits within the 2. Pilot Switch - To holding coil of a starter when switch’s electrical rating. the burner circuit exceeds the switch’s electrical rating. -
Page 10: Installation Complete
STEP 4 - Testing This control is factory calibrated for specific level The following testing procedure is only meant to settings as shown on pages 2-4 in the “Operation” serve as a verification of proper operating section. sequence. IMPORTANT: Follow the boiler manufacturer’s start-up and operating instructions along with all applica- ble codes and ordinances. -
Page 11: Maintenance
MAINTENANCE BLOW DOWN PROCEDURE: SCHEDULE: CAUTION Blow down control as follows when boiler is To prevent serious personal injury from steam in operation. pipe blow down, connect a drain pipe to the • Daily if operating pressure is above 15 psi. control opening to avoid exposure to steam discharge.
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