Specifications

16 IM 685-2
Gas Valve Pressure Regulator Adjustment
The high turndown burner uses combination gas controls to
provide redundant on-off gas control and pressure regulation.
A burner will have from one to six of these controls piped in
parallel depending on the BTU rating of the burner. When
two or more valves are in parallel their pressure regulators
must be adjusted so the valves maintain the specified mani-
fold pressure and are balanced so each valve handles its share
of the load. To determine that the valves are balanced, the
manifold pressure must be measured and adjustments made
at both maximum and minimum capacity. As the burner mod-
ulates from maximum capacity down to minimum capacity it
is normal for the manifold pressure to rise. This is because
the pressure loss through the valve and fittings is being
reduced as the flow rate is reduced. If one (or more) valve is
not in balance with the others, the pressure at the minimum
rate will rise higher than normal.
Clockwise rotation of the pressure adjusting screw on the
combination gas controls will increase the pressure set point,
and counter-clockwise rotation will reduce the pressure set
point (see Figure 11).
Figure 11. Combination Gas Controls
Adjustment Procedure for Parallel Valves
When a manifold pressure adjustment is required, the first
step is to adjust the pressure regulator of each combination
gas control to the minimum rate manifold pressure (Table 7,
Column 10) while only that valve is operational, and it is
handling approximately its normal maximum rate CFH of
gas. The manual shutoff valve knobs are used to control gas
flow so just one valve is operating at a time.
To determine a firing rate suitable for this adjustment, first
modulate the burner down to the minimum rate. At this flow
rate only the valve with the highest pressure regulator set
point will be operational, the other valves will be shut down
by their integral pressure regulators because the manifold
pressure is slightly higher than their set point. While the
burner is operating at that minimum firing rate slowly close
all but one of the manual shutoff valve knobs on the combi-
nation gas controls. With care this can be done without the
burner loosing flame and shutting down. Watch the manifold
pressure manometer as each valve is being closed. If the
manifold pressure starts to drop rapidly in response to the
knob movement, it indicates this combination gas control has
the higher pressure adjustment and is supplying the gas to the
manifold. Leave this valve open, and continue closing the
remaining valves until only that one valve is open, and then
adjust that combination gas control first.
While the burner is operating and only one combination gas
control is open, increase the firing rate of the burner. As the
firing rate is increased the manifold pressure will be rela-
tively constant until the gas flow rate exceeds the capacity of
that single valve and the manifold pressure starts to drop off.
The pressure adjustments should be made at the maximum
gas flow rate just before the manifold pressure starts to drop
off, and the following should be considered:
a. The manifold pressure does not always immediately
respond to regulator adjustments. Wait a few seconds after
making an adjuster movement for the regulator to respond
and equalize.
b. When making an adjustment rotate the adjuster CCW
until the manifold pressure is below the desired set point,
and then slowly rotate the adjuster CW and nudge the
pressure up to the desired set point.
c. If the regulator cannot be adjusted up to the required set
point, or if that set point seems to be the highest pressure
the regulator can be adjusted to, the flow rate used for this
procedure is too high and must be reduced by reposition-
ing the actuator to a lower firing rate, or the gas supply
line pressure is too low.
After adjusting valve 1, open valve 2. If opening the addi-
tional valve does not cause the manifold pressure to go up,
increase the pressure regulator setting of valve 2 until an
increase is observed, this would indicate that the valve has
started functioning. Then slowly close the first valve. Pro-
ceed to adjust valve 2. Repeat this procedure until all valves
have been adjusted.
Open the manual shut off knobs on all the combination gas
controls and modulate the burner up to the maximum firing
rate. The resulting manifold pressure should be close to the
Maximum Rate Manifold Pressure indicated in Table 7, Col-
umn 6. If further adjustment is required it should not be nec-
essary to go through the entire procedure again. If the
manifold pressure is to be increased, make small but equal
(about 1/4 revolution) CW rotations of the pressure adjusting
screw on every combination gas control and check the result-
ing manifold pressure, both at maximum and minimum rate.
Check Manifold Pressure at Minimum Rate
When several combination gas controls are in parallel and are
handling a low flow rate, the combination gas control with
the highest set point is essentially handling all the gas.
Observe the gas manifold pressure at the minimum rate. If it
is higher than the pressure specified under Column 10 in
Table 7, locate and adjust the dominant combination gas con-
trol. Test each combination gas control by slowly manipulat-
ing the manual shutoff knob toward the closed position while
observing the manifold pressure. The pressure will only
respond to movement of the knob on the dominant valve. The
manifold pressure will drop as the gas flow is throttled back,
using the knob on the combination gas control to partially
close that manual valve.
PRESSURE REGULATOR ADJUSTMENT
(UNDER CAP SCREW)
INLET
PRESSURE
TAP
GAS
CONTROL
KNOB
OUTLET
PRESSURE
TAP
(SHOWN AT "ON")
INLET
OUTLET
ON
OFF