Page 20 / IM 685
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 5, 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 combination gas controls. With care this can
be done without the burner losing 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 relatively 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 reglator can be adjusted to, the flow rate used for this procedure is too
high and must be reduced by repositioning 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 additional 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. Proceed 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 5, Column 6. If further adjustment is required it should not be necessary 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 resulting 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 setpoint 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 5,
locate and adjust the dominant combination gas control. Test each combination gas control by slowly
manipulating 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.
Generally a valve will be found that has an effect, and very little adjustment will cause a reduction in the
minimum rate manifold pressure. Reduce the pressure adjustment of that dominant valve by slowly
rotating the adjuster CCW until the manifold pressure no longer drops in response to that adjuster
movement.If the manifold pressure is still high after that first adjustment, another valve may have
become the dominant valve and that may also have to be isolated and adjusted to get down to the
specified minimum rate manifold pressure. After making this type of adjustment it is necessary to
recheck the maximum firing rate manifold pressure and perhaps readjust it, making very small but equal
adjuster movements on each valve.
