Xylem MM 404J Series 93/193 and Series 94/194 Low Water Cut-Off/Pump Controllers For Steam Boilers and Level Control Applications - Manual (Page 11)

©2008 ITT Corporation
Printed in U.S.A. 12-08 246043
ITT
8200 N. Austin Ave.
Morton Grove, IL 60053
tel: 847-966-3700
fax: 847-966-9052
www.mcdonnellmiller.com
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 creates 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.
Valve #2
Valve #1
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.
11
STEP 6 - Testing
a. Turn on power to boiler and pump circuits.
With the boiler empty, the pump should turn on (5
or 5-M switch models) or the valve open (7B or
7B-M switch models). The burner should remain off
and boiler should begin to fill with water.
b. For Automatic Reset Models
When water level in the gauge glass is approximately
1 3/8” (35mm) above the horizontal cast line, the
burner should turn on.
For Manual Reset Models
When water level in the gauge glass is approximately
1 3/8” (35mm) above the horizontal cast line, press
the manual reset button and the burner should turn on.
c. For 5 or 5-M Switch Models
When water level in the gauge glass is approximately
2 3/16” (56mm) above the horizontal cast line, the
pump should turn off.
For 7B or 7B-M Switch Models
When water level in the gauge glass is approximately
2 3/16” (56mm) above the horizontal cast line, the
valve should be closed.
d. With the water in the boiler at its normal level and
burner on, SLOWLY open the blow-down valve
until it is fully open. As the water level in the gauge
glass begins to drop, verify that the following occurs.
For 5 or 5-M Switch Models
When water level drops to approximately 1 1/8”
(29mm) above the horizontal cast line, the pump
should turn on. When water level drops to the hori
zontal cast line, the burner should turn off.
For 7B or 7B-M Switch Models
As the water level drops, the valve should begin to
open. When the water level drops to approximately
1 1/8” (29mm) above the horizontal cast line, the
valve should be full open.
When the water level drops to the horizontal cast
line, the burner should turn off.
e. Close the blow-down valve after burner turns off
and restore water level to normal operating level.
f. Repeat testing procedure several times to ensure
proper operation of control.
g. After testing and verification of control operation,
the boiler can be returned to service.
– Dimensions shown are typical.
– The following testing procedure is only meant to serve
as a verification of proper operating sequence.
CAUTION
Immediately turn off all power if the burner turns on
with no water in the gauge glass. Investigate further
before continuing procedure.
!
CAUTION
If pump does not turn off or valve close, turn off
water supply to boiler. Investigate further before
continuing procedure.
!
TROUBLESHOOTING
Erratic operation of the control is the most common symptom
that occurs. Erratic operation can be defined as pump and/or
burner switches not switching at proper levels. Refer to the
following list of items to check if the control is not operating
properly.
1. Float Ball is Crushed
Crushed floats are typically caused by improper blow-
down. Drain piping from blow-down valve to drain should
be checked for proper pitch and the blow-down procedure
followed when blowing down the control. Purchase and
install a new float ball after investigating and correcting
the problem.
2. Float Ball is Filled with Water
The seam weld on the float can sometimes deteriorate.
This can be caused by the type of chemical treatment
used in the boiler. While this is a rare occurrence, the
chemical treatment supplier should be consulted to deter-
mine if a reaction could occur. Purchase and install a new
float ball after investigating and correcting the problem.
3. Float Arm Springs are Bent
The pivot springs located on either side of the float rod
should be flat and straight. If they become bent, the usual
cause is mishandling of the unit during installation or
improper blow-down. The control should never be picked
up by the float ball or allowed to hang from the bowl by the
float. Drain piping from blow-down valve to drain should be
checked for proper pitch and the blow-down procedure
followed when blowing down control. Purchase and install
new control or head mechanism after investigating and
correcting the problem.
4. Switch Contact Springs Broken
The contact springs can break if the electrical rating is
exceeded. Purchase and install new switch assembly or
head mechanism after investigating and correcting the
problem.
5. Switch Contact Springs Misaligned
Misalignment of the contact arms is usually associated
with damage to the control during shipment or installation.
Purchase and install new switch assembly or head
mechanism after investigating and correcting the problem.
6. Internal (Wetted) Parts Dirty
The internal parts can operate improperly if dirt, scale or
rust is allowed to build. This condition can be a result of
not blowing down the control as recommended and/or
improper boiler water chemical treatment. Purchase and
install new control or head mechanism after investigating
and correcting the problem.