Replacement Parts List

24
Boiler Control Replacement Parts
McDonnell & Miller
B
OILER
C
ONTROLS
Low Water Cut-Off/Pump
Controllers For Steam Boilers
Series 150, 150S & 150E
Series 157, 157S & 157E
Two Series of LWCO controls (Series 150S and
Series 150E) are available as alternatives for Series
150 LWCO controls that contain mercury switches.
Please keep in mind that in a replacement or repair
situation you do not have to change out the entire
control. A head replacement (i.e. 150E-HD or 150S-
HD) is all that’s required.
There may be additional letters such as ‘B’, ‘R’, ‘RL’,
etc. in the sales catalog designation of the control.
These additional letters designate tapping locations
and sizes which have no affect on which head mech-
anism to purchase. All head mechanisms are inter-
changeable and can be installed on any body.
‘MD’Models
The ‘MD’ model should be used as a replacement
head when the boiler operating pressure is less than
50psi. These were created to provide a control with
factory settings to compensate for the narrowing of
setpoints. The larger differential between pump on
and burner off reduces the potential for nuisance
burner shutdown.
It is important to understand that regardless
of which control is used (Series 150E or 150S),
there are requirements that lead to the best
performance of ALL level controllers and LWCO’s:
• Use of properly-sized pump starters/relays
in the pump control circuitry
• Pumps that are balanced to the system
requirements
• Equalizing piping, per the boiler manufacturer’s
recommendations, to properly sense the
boiler water level
• Industry accepted blowdown piping to provide
best cleaning action of the control chamber, float
linkage mechanism and/or probes
• Proper periodic blowdown of the boiler controls.
• Proper chemical treatment of boiler water.
• Annually cleaning and careful exam-
ination of the float mechanism, probes, and
electrical switches or controls. More frequent
cleaning may be required for exceptionally
dirty steam systems.
150 or 150S
Float Chamber Body
157 or 157S
Water Column Body
150E
Float Chamber Body
157E
Water Column Body
MM-701A_FINAL.qxd 7/15/08 12:34 PM Page 24