Garland 40 Series Technical Reference Manual - page 103
Part # GCTRM Rev 3 (12/10/09)
Page 103
Page 2 of 2
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Garland uses a fixed drilled orifice to regulate the first stage in the SIT Control as
shown below.
When a call for heat is initiated, the thermostat will cycle as follows:
First stage, as
shown below, begins when the thermostat applies light pressure to the base of the
valve assembly. The greater the degrees for the thermostat to rise to set point, the
higher the pressure will be. When higher pressure is applied to the base of the valve
assembly, the second stage begins. The second stage raises the entire valve
assembly.
As the control approaches set point, the valve assembly lowers, modulating the
flame, until it completely closes, leaving the fixed flame of the first stage to continue
Until all pressure is removed and valve assembly is fully closed as shown below.
So to review, first stage is a fixed flame based on an orifice within the control and
second stage is modulating, based on variable valve assembly positioning. Both
snap closed when the thermostat satisfies the call for heat by relieving the pressure
from the Valve Assembly.
(Internal component shown,
do not disassemble control)
(Internal component shown,
do not disassemble control)
(Internal component shown,
do not disassemble control)
Orifice
1st
2nd
4th
3rd