11
Eclipse ThermJet Design Guide No. 205, 3/5/07
Control Methods
There are two main methods to control the input of a Therm-
Jet system. Each of these methods also has two variants. These
methods may be applied to single burner as well as multiple
burner systems.
The methods and variants are:
1. Modulating control
Modulating gas & air, on-ratio control or excess air @ low
fire
on page 12.
Modulating gas with fixed-air control
on page 13.
2. High/low control
High/low air & gas control (pulse firing)
on page 14.
High/low gas with fixed-air control (Can also be used for
pulse firing)
on page 15.
Note:
Use of a ratio regulator in a fixed-air system is optional. How-
ever, eliminating the ratio regulator will adversely affect the
ignition reliability at inputs greater than 40% of maximum.
Use of a ratio regulator in a fixed-air system also provides
automatic gas modulation if system air flow changes over
time (such as a clogged air filter).
In the pages that follow you will find schematics of these control
methods. The symbols in the schematics are explained in the
“Key to System Schematics” (see Appendix).
Automatic gas shut-off by burner or shut-off by zone
The automatic gas shut-off valve can be installed in two opera-
tional modes:
Automatic gas shut-off by burner
If the flame monitoring system detects a failure, the gas shut-
off valves close the gas supply to the burner that caused the
failure.
Automatic gas shut-off by zone
If the flame monitoring system detects a failure, the gas
shut-off valves close the gas supply to all the burners in the
zone that caused the failure.
Note:
All ThermJet control schematics on the following pages reflect
a single gas automatic shut-off valve.
NC
This may be changed to conform to local safety and/or insur-
ance requirements (Refer to page 9 of ThermJet Installation
Guide No. 205).
a.
b.
a.
b.
1.
2.
Step 2:
Control Methodology
(continued)
