Gas/Propane Basics
The Gas Side
As we look into some more modern systems and
what specific problems they present, it is important
to understand the basic fundamentals
associated with these systems.
Most of our modern heating equipment in some way
or another involves electronics, and with the electronics,
the use of Flame Rectification as a safety and
flame-proving system.
It does not matter if it is a forced warm air furnace
or a forced hot water boiler—the same basic system
is used to perform safe ignition and then consistent
operation throughout the entire call for heat.
There are however different ways it is applied from
Intermittent Pilot Application to Direct Spark Ignition
and including Hot Surface Ignition. Each has its own
distinct advantages and problems.
I invite you to visit our new Facebook page, Timmie’s
Tips on Gas, located at facebook.com/groups/timmiesgastips.
I look forward to seeing you there.
Universal Gas Valves Systems
In this section we are going to discuss Universal Gas
Valves systems—in particular the Robertshaw 720-079
Gas Valve Uni-Kit. We will present some of the basics
initially, then the installation and finally get into
troubleshooting.
The 720-079 is designed to work equally well on
Intermittent Pilot, Direct Spark and Hot Surface Ignition.
Its features include:
• Dual automatic valves (redundant)
• Wiring connections, manual selector and
Timmie McElwain
President, Gas Appliance Service
timmcelwain@gastcri.com
adjustments on top of the valve
• Meets all codes requiring dual valve safety shutoff
• Reduces service truck stock-freeing up valuable
space and saving money.
The 720-079 shown in Figure 1 features a manual
selector, wiring connections and adjustments that
are all easily accessible on the top of the valve. The
720-079 Uni-Kit has 1/2" side outlets and a pressure
regulator that is preset at 3.5" water column (WC) for
natural gas. For liquefied petroleum (LP) gas applications,
the valve can be converted by using a pressure
regulator conversion kit that is included.
The 720-079 incorporates a manual valve, pilot valve
(dual automatic valves) and a main gas pressure regulator
all in a small compact valve with a swing radius
of 3–9/16". The small size of the 720-079 lends itself
to replacing many original equipment manufacturer
(OEM) and competitive valves. The 720-079 is multiposition
and can be mounted in any position, except
upside-down.
Figure 2
The red manual selector arm easily identifies the
720-079 shown in Figure 2. In fact, all Robertshaw
7200 series valves with this arm are dual seated
valves. The valve also features side outlets, which can
be plugged if not used. Also illustrated are the inlet
Figure 1
14 ICM/March/April 2021