Xylem MM 221G User Manual

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INSTRUCTION MANUAL

MM-221G

Model 157S-RBP-MD

(Snap Switch)

Low Water Cut-Off/Pump Controller

Applications: For bi-level pump control applications such

as multiple boiler level operation.

CAUTION

WARNING

• 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.

Model 157S-RBP-MD

WARNING

Pump or Motorized Valve

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 5

/2 (140)

/2(38)

Pump On 4 (102)

Pump Off

/16 (24)

/8(16)

Pump On

/16 (14)

Burner Off 0 N/A

Pump Off 17/16 (37)

/4(19)

Pump On

/16 (17)

Burner Off -

/8 (-16) N/A

PUMP OFF

CAST LINE

/8"

(35mm)

/16"

(16mm)

PUMP ON

BURNER OFF

CASTING LINE

PUMP ON

PUMP OFF

;

11/2"

(38mm)

(102mm)

OPERATION

Maximum Pressure: 150 psi (10.5 kg/cm2)

Electrical Ratings Float Control

Probe Control (750BM-P-120-CI)

157S-RBP-MD

Settings and Differential Pressures:

Probe Sensitivity:

- 26,000 ohms

Probe Input Power

- 120 volts

Pump or Motorized Valve

Circuit Rating (Amperes)

Voltage Full Load Locked Rotor

120 VAC 7.2 43.2

240 VAC 3.75 21.6

Probes Any

Pressure

Float 0 psi

(0 kg/cm

)

Float

150 psi

(10.5 kg/cm2)

Pressure

Alarm Circuit Rating

Voltage Amps

120 VAC 1

240 VAC 1/2

Motor Horsepower

Voltage Amps

120 VAC 1/3

240 VAC 1/3

* Values are ± 8" (3.2mm).

Probe Settings

Float Settings (0 psi)

NORMAL BOILER WATER LINE

“CUT-OFF” LEVEL AT CAST LINE

11/2"

(38mm)

MINIMUM SAFE WATER LEVEL

BLOW DOWN VALVE

Size the steam (top) and water (bottom) horizontal equalizing pipe lengths so that the horizontal cast line on the body is 12" (38mm) below the boiler’s normal water level, but not lower than the minimum

safe 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.

a. Using a pipe wrench, unscrew the plastic float

blocking plug (A) from the float block tapping of the low water cut-off body (B).

Install pipe plug (provided) to seal port.

STEP 2 - Installing the Low Water Cut-Off

b. Mount and pipe the low water cut-off (C) on a

vertical equalizing pipe (D) at the required elevation level, as determined in Step 1.

Install full ported blow down valves directly below the lower cross of the water equalizing pipe (F).

NORMAL BOILER WATER LINE

BLOW DOWN VALVE

The plug must be reinstalled before control is shipped installed on the boiler, and removed when boiler is installed after shipment.

Failure to follow this caution may damage float and operating mechanism

CAUTION

STEP 3 - Electrical Wiring

a. Using a flathead screwdriver, remove the

junction box cover (K) by unscrewing the four (4) cover screws.

• To prevent electrical shock, turn off the electrical power before making electrical connections.

• Modification of the switch assembly before or after installation could cause damage to the boiler and/or boiler system.

• Boiler manufacturer schematics should always be followed. In the event that the boiler manufacturer’s schematic does not exist, or is not available from the boiler manufacturer, refer to the schematics provided in this document.

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

Switch Operation - Float Control

Switch Operation - Probe Control

Boiler feed pump off,

burner on, alarm off.

Boiler feed pump on,

burner on, alarm off.

Boiler feed pump on,

burner off, alarm on.

1 2 4 5 6 1 2 4 5 6

Water “ON” High Probe

HIGH

PROBE

LOW

PROBE

COMMON

N.C. CONT.

N.O. CONT.

GND

1 2 4 5 6

Water “OFF” Low Probe

HIGH

PROBE

LOW

PROBE

COMMON

N.C. CONT.

N.O. CONT.

GND

b. Following the appropriate wiring diagram, (refer

to page 6) based on your application requirements, and using BX armored cable or Thinwall electrical metal tubing connector fittings, make electrical connections to the junction box (L).

PUMP SWITCH

PUMP

CIRCUIT

TERMINALS

LOW WATER CUT-OFF AND ALARM SWITCH

ALARM

CIRCUIT

TERMINALS

LOW WATER

CUT-OFF

TERMINALS

IMPORTANT: There must be a minimum space of 1/2" (13mm) between connector fittings and electrical live metal parts.

• Mount 750BM module using 8 pin socket base (supplied by others) in Boiler Electrical Panel.

• Install electrical conduit between

Probe Housing and Boiler Electrical Panel.

• Pull three (3) wires through conduit.

Boiler sight glass must be visible from location of Control Box and must be within 25 feet of Control Body.

NOTE

Refer to and follow local codes and standards when selecting conduit and electrical fittings. Probe wires must be in their own conduit. If they are run in conduit with other wires, there may be interference that can affect the performance of the control.

NOTE

Wire must be 18 AWG stranded with glass braided silicone jacket (UL 3071) suitable for high temperature (200˚C) service.

NOTE

Snap Switches (Series 150S)

Installation of 750BM-P-120-CI

WIRING DIAGRAMS

LINE

Low Water Cut-Off Only

1. Main Line Switch - For burner circuits within the switch’s electrical rating.

LINE LOAD

12 456

Pump Control Only

1. Instal 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.

Alarm Circuit Only

1. Low Water Alarm

ALARM

NEUTRAL

12 456

HOT

2. Pilot Switch - To holding coil of a starter when the burner circuit exceeds the switch’s electrical rating.

12 456

LOAD

NOTE: To help insure most effective operation, balance boiler feed pump(s) to deliver required water feeder rate to match boiler steaming requirements.

LINE

12 456

LOAD

2. High Water Alarm

ALARM

NEUTRAL

HOT

12 4 56

Combination Pump Control, Low Water Cut-Off and Alarm

1. Main Line Switch - For burner circuits within the switch’s electrical rating.

SEE PUMP CONTROL

CIRCUIT

12 456

ALARM

TO BURNER CONTROL CIRCUIT

HOT

TO NEUTRAL

ELECTRONIC PROBES:

HIGH

PROBE

AC SUPPLY

LOW

2. Pilot Switch-To holding coil of a starter when the burner circuit exceeds the switch’s electrical rating.

Pump

COMMON

N.C. CONT.

N.O. CONT.

GND

Securely tighten all electrical conductors to terminals

SEE PUMP

CONTROL

CIRCUIT

12 456

HIGH

LEVEL

PROBE

ALARM

CONTROL

LOW

LEVEL

PROBE

LINE (3 PHASE)

LOAD

STEP 4 - Testing

Standby Range Operation:

OFF

a. Turn on the electric power to the boiler. The pump should go

on and the burner must remain off.

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. If the burner does not turn on or pump turn off at appropriate levels, immediately turn off the boiler and make the necessary corrections.

c. Blow down the control when the water in the boiler is at

its normal level and the burner is on. Slowly open the upper then the lower blow-down valves and observe the water level fall in the sight glass. Close the valves (lower first then upper) after verifying that the pump contacts have closed and the burner shuts off. If this does not happen, immediately shut off the boiler, correct the problem and retest.

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 page 2 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

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

MAINTENANCE

BLOW DOWN PROCEDURE:

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.

NOTE

More frequent blow-down may be necessary due to dirty boiler water and/or local codes.

• 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.

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

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.

CAUTION

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.

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.

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 Inc.

8200 N. Austin Avenue Morton Grove, Illinois 60053 Phone: (847) 966-3700 Fax: (847) 965-8379 www.xyleminc.com/brands/mcdonnellmiller

Xylem MM 221G User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual