Adjustment Procedures
5-4
750-96 (revised 2010)
Model CB Packaged Boiler Manual
The amount of angular movement controlling the rate of air flow is determined by the location of the ends of the
rotary air damper rod in both the jackshaft arm and the air damper arm.
When the air damper is in low fire position, both the jackshaft arm and the rotary air damper arm should make an
angle of approximately 60º below the horizontal. This is to insure that the angular movement of the damper starts
slowly, increasing in speed as the high fire position is approached.
Prior to initially firing a boiler it is advisable to check for free movement of the linkage. The damper motor must be
allowed to complete its full stroke and the damper must move from low to high fire position.
Adjustment of linkage connected to a gas butterfly valve is described in Section 5.17.
5.3 — Modulating Motor: Honeywell M954B or M954C
The modulating motor used in this application has a 90º shaft rotation. The motor manufacturer also provides a
160 stroke model for other applications. If a replacement is not obtained from a Cleaver-Brooks Service-Parts
Agency, it may have an incorrect stroke. To prevent damage, determine the 90º stroke prior to installing a replace-
ment.
This may be determined either by visual inspection of the power end shaft or by powering the motor and connect-
ing terminal R-B to actually determine the stroke as the motor drives to an open position.
The closed position of the motor (normal condition of replacement motor) is the limit of counterclockwise rotation
as viewed from the power end of the motor. In this position the flat part of the shaft is 45º from the horizontal on
90º stroke motors and 10º from horizontal on 160º stroke motors.
If adjustment to the stroke is required, refer to the manufacturer’s Technical Bulletin. The motor may be damaged
if it is unable to complete its full stroke.
5.4 — Modulating Motor Switches: Low and High Fire
The modulating motor contains either one or two internal switches depending upon application. These single pole
double throw micro-switches are actuated by adjustable cams attached to the motor shaft.
Factory replacement motors have the cams preset. The low fire start switch is set to make the red and yellow
leads at approximately 8º on motor closing. The high fire purge air proving switch (M954B motor) is set to make
red and blue tracer leads at approximately 60º on motor opening. Normally, these settings are left as is but job
conditions may require readjustment.
If the cams require adjustment or resetting, follow the instructions in the manufacturer’s Technical Bulletin.
Courtesy of: C3 Surplus LLC
Surplus Industrial Superstore
305-428-2777
https://www.c3surplus.com
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