Testing Gas Supply Pressure; Check Manifold Pressure; Left Side Piping; Right Side Piping - Lennox G26 series User Manual

LEFT SIDE PIPING

MANUAL MAIN
SHUT−OFF
VALVE
GAS VALVE
FIGURE 45
IMPORTANT
In case emergency shutdown is required, turn off
the main shut-off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
When checking piping connections for gas leaks, use pre-
ferred means. Kitchen detergents can cause harmful corro-
sion on various metals used in gas piping. Use of a specialty
Gas Leak Detector is strongly recommended. It is available
through Lennox under part number 31B2001. See Corp.
8411−L10, for further details.
GAS VALVE

RIGHT SIDE PIPING

(STANDARD)
Page 30
Do not use matches, candles, flame or any other source of
ignition to check for gas leaks.
E−Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to
inlet pressure tap (field provided). See figure 44. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas valve or
overfire. For natural gas units, operating pressure at unit
gas connection must be between 4.5" W.C. and 13.0" W.C.
For L.P. gas units, operating pressure at unit gas connec-
tion must be between 8.0" and 13.0" W.C.
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres-
sure must fall within range listed in previous paragraph.
F−Check Manifold Pressure
Manifold Operating Pressure is the manifold pressure
measured during normal operation (sensing burner box
pressure). Manifold Absolute Pressure is the manifold
pressure measured when the gas valve regulator is oper-
ating at factory preset level (sensing atmospheric pres-
sure).
After line pressure has been checked and adjusted, check
manifold absolute pressure. Move pressure gauge to out-
let pressure tap located on unit gas valve (GV1). Checks of
manifold absolute pressure are made as verification of prop-
er regulator adjustment.
Manifold operating pressure for the G26 can be measured at
any time the gas valve is open and is supplying gas to the
unit. Normal manifold operating pressure for natural gas
units is 2.5 to 3.5 in. w.c (see figure 21). For LP/propane gas
the correct manifold operating pressure is 7.5 in. w.c. (see
figure 22).
IMPORTANT
For safety, connect a shut-off valve between the
manometer and the gas tap to permit shut off of
gas pressure to the manometer.
The gas valve is factory set and should not require adjust-
ment. See table 9. Also, gas valve regulation varies with
burner box pressure (figures 21 and 22).
*Manifold Absolute Pressure Measurement and Adjust-
ment
1 − Connect test gauge to outlet tap on gas valve.
2 − Disconnect pressure sensing hose from gas valve
and plug hose. Leave hose barb on valve open to at-
mosphere. See figure 46.
3 − Start unit and allow 5 minutes for unit to reach steady
state.