Aerovent IM-500 - Manual (Page 7)

7 Aerovent IM-500
11. Purge air from gas piping before lighting unit.
12. After air has been purged, check for gas leaks in the
piping system using a soap water solution.
13. Install a ground joint union and gas cock external of
the unit for easy servicing of controls.
14. Allow at least 5 feet of piping between any high pres-
sure regulator and the unit control pipe train.
Gas Supply Pressure – 5 lbs. or less
The Aerovent air make-up unit is standardly furnished with
the Maxitrol modulating system. This device controls the
firing rate of the burner to maintain the desired operating
temperature.
It functions as a regulator and modulator which will not
allow the burner manifold pressure to exceed that which
produces the maximum firing rate, and also will reduce the
pressure below this value to modulate the burner through-
out the normal 25 to 1 turn down ratio. The upstream
pressure supplied to the unit pipe train must not exceed 5
pounds. This is the maximum for suitable operation. The
minimum operating pressure will vary depending upon the
unit size and pipe train size. This pressure is marked on
the pressure gauge. As long as the gas pressure supplied to
the unit is maintained at some value between the minimum
as marked on the gauge and 5 pounds maximum, the air
make-up unit will perform at its rated capacity.
If the gas supply system is designed for a pressure
higher than 5 pounds, it is necessary to install an additional
regulator upstream of the connection to the unit. See fol-
lowing instructions for gas supply over 5 pounds.
The downstream pressure from the line regulator will
vary somewhat depending upon the firing rate of the air
make-up unit. Variations can also be caused by other gas
equipment connected to the distribution system. It is neces-
sary, therefore, to be sure that the setting of the supply line
regulator is such that the pressure supplied to the unit will
always be at least equal to the minimum and not exceeding
5 psi.
NOTE:
DO NOT VENT THE VENT VALVE AND PRESSURE
REGULATOR IN THE SAME VENT PIPE. SEPARATE
VENT LINES TO OUTSIDE ATMOSPHERE MUST
BE RUN FOR THE UNIT TO OPERATE PROPERLY.
COMBINING THE VENT LINES TO ATMOSPHERE
WILL CAUSE THE HIGH LIMIT GAS PRESSURE
CONTROL TO LOCK OUT THE FLAME SAFETY
SYSTEM AND SHUT DOWN THE UNIT.
NOTE:
A PRESSURE REGULATOR MAY BE REQUIRED TO
MEET THE STATE OR LOCAL CODE. CONSULT
YOUR STANDARDS.
Gas Supply Pressure – Over 5 lbs.
When the supply line pressure to an air make-up unit
exceeds 5 pounds or may at times fluctuate above 5 pounds,
it is necessary to install a line pressure regulator ahead of
the input to the air make-up unit. The size must be selected
to handle the maximum capacity of the unit, and the type
of regulator selected to work at the maximum inlet pressure
and having a capability of maintaining the outlet pressure
at some value between 8 ounces and 5 pounds. As a rule,
the outlet pressure from the line pressure regulator may be
adjusted anywhere between 2 and 4 pounds. If the regula-
tor was furnished by Aerovent, it has been sized according
to the information in the original order and shown on the
parts list. Regulators are sized according to capacity and
pressure and not according to pipe size; therefore, the size
of the pipe at the inlet to the air make-up unit may not be
the same as the pipe size of the regulator.
To be sure the supply line is properly sized, it is sug-
gested that the representative of the local gas company be
consulted about pipe sizing. The line regulator should be
installed close to the air make-up unit. There should be no
elbows, couplings, valves, or fittings within at least ten pipe
diameters of the inlet and the discharge of the pressure
regulator. A shut-off cock should be placed upstream of
the regulator so that it can be removed for servicing if nec-
essary. It is a good idea, also, to install a pressure gauge on
the upstream side having a scale range sufficient to indicate
the supply line pressure.
It is very important to connect the regulator vent with
pipe or tubing extended to the outside with the end pro-
tected from the weather. Do not vent the regulator into the
air make-up unit or the duct system, or near the inlet to the
air make-up unit.
NOTE:
DO NOT VENT THE VENT VALVE AND PRESSURE
REGULATOR IN THE SAME VENT PIPE. SEPARATE
VENT LINES TO OUTSIDE ATMOSPHERE MUST
BE RUN FOR THE UNIT TO OPERATE PROPERLY.
COMBINING THE VENT LINES TO ATMOSPHERE
WILL CAUSE THE HIGH LIMIT GAS PRESSURE
CONTROL TO LOCK OUT THE FLAME SAFETY
SYSTEM AND SHUT DOWN THE UNIT.
Figure 1. Typical Gas Regulator