Overview of Primary Product

1
Series 20 & 21 Condensed Catalog
Electronic Modulation Gas-Fired Temperature Controls/Indirect Fired Applications
© 2014 Maxitrol Company, All Rights Reserved
DESCRIPTION
Selectra
®
systems from Maxitrol maintain precise, stable
gas-red temperatures. Selectra’s unique electronic
Modulator-Regulator valves control gas ow with
instantaneous response and continual adjustment. They
are the superior alternative to mod motors and buttery
valves.
OEM or retrot applications include environmental
climate control, as well as industrial or commercial
heating processes. Suitable for application in natural,
manufactured, mixed gases, liqueed petroleum gases
and LP gas-air mixture piping systems.
Available standard companion electronics include
temperature selectors, ampliers, and temperature
sensors, in a variety of congurations. The amplier
supplies output voltage to the MR valve.
SPACE HEATING APPLICATIONS
Series 20 System (replaces Series 20/30)
Selectra
®
Series 20 electronic gas ame modulation
systems are designed primarily for commercial and light
industrial space heating, as components of indirect red
units with atmospheric burners.
Combining the capability of the Series 20 and 30, the
current Series 20 is designed for single or multiple (up to
four) furnace operations. It may be eld installed on existing
equipment or specied for new equipment installation.
The system uses Modulator-Regulator valves. High
Fire ignition selection (0, 5 or 25 second) is standard on
all models. A wall mounted Selectrastat senses space
temperature and has an integral selector with a 60° to 85°F
range. Optionally, a remote Temperature Sensor paired
with a separate Temperature Selector (60° to 85°F) can be
substituted for the Selectrastat.
MAKE UP AIR APPLICATIONS
Series 21 System (replaces Series 21/31)
Selectra
®
Series 21 electronic gas ame modulation
systems are designed primarily for make-up air heating,
as components of indirect red units with atmospheric
burners.
Combining the capability of the Series 21 and 31, the
current Series 21 is designed for single or multiple (up to
four) furnace operations. It may be eld installed on existing
equipment or specied for new equipment installation.
The system uses Modulator-Regulator valves. Ampliers
are available with integral or remote temperature selection.
High Fire ignition selection (0, 5 or 25 second) is standard
on all models. A discharge air temperature sensor is
mounted within a mixing tube housing. Optionally, a room
override thermostat when used in conjunction with the
remote temperature selector provides space temperature
control by raising the discharge air temperature to a
pre-selected point.
Also optional, an inlet air sensor (and mixing tube) provides
inverse change in discharge air for each degree change
in inlet air - when installed in a convenient duct location
upstream of the burner.
MR610
Figure 1: MR Valves
MR510
MR410