Reznor PDH Operation Manual PreevA - Manual (Page 15)

Form O-PreevA, P/N 234661R8, Page 15
Instructions for checking valve shutoff:
1) Locate the 1/8” NPT pressure tap on the combination valve (FIGURE 5).
2) With the manual valve turned off to prevent flow to the gas valve, connect a
manometer to the 1/8” outlet pressure tap in the valve. NOTE: A manometer (fluid-
filled gauge) is recommended.
3) Turn the manual valve to the ON position and the heater OFF. Use your finger to
fully block the main burner orifice for several seconds. Observe the manometer
with the orifice blocked. If any pressure is indicated, the gas valve is leaking.
A leaking gas valve must be replaced before the heater is put back in
operation.
Single-Stage
Valves
1/8” Outlet Pressure Tap
FIGURE 5 - Pressure
Tap for Checking Gas
Flow Shutoff
Two -Stage Valve
1/8” Outlet Pressure Tap
Modulating Gas Valve
and Gas Pressure
Switch - Options AG40,
DG2, DG6, D12B
Function: The gas valve controls modulation and
the gas pressure switch monitors gas pressure to
control operation of the two-speed venter.
Service: The modulation gas valve and switches
have no field maintenance requirements except
careful removal of external dirt accumulation and
checking of wiring connections.
Use only factory-authorized parts.
Location: See FIGURE 1A, page 5, for location.
CAUTION: DO NOT
bottom out the gas
valve regulator
adjusting screw.
This can result in
unregulated manifold
pressure causing
excess overfire and
heat exchanger
failure.
Modulating Gas Valve -
Options AG58, D12G
The gas train has a ball valve with an actuator (see FIGURE 6) to control gas flow. The
ball valve and actuator are located downstream of the combination single-stage valve
as shown in FIGURE 4.
Carefully clean external dirt accumulation from the actuator.
Ball Valve with actuator removed
Ball Valve Shaft Ball Valve Actuator Modulates the Gas Flow
Actuator Set Screw
(shown on the right
or closed position)
FIGURE 6 -
Ball Valve and
Actuator in
Gas Control
Options AG58
and D12G
Natural Gas
Pressure
Switch ,
P/N 211130
Propane
Pressure
Switch ,
P/N 211710
Valve
Modulating System Gas
Valve (Ball Valve and
Actuator) Adjustment
Inspect the position of the ball valve shaft.
•
In the fully open position, the dash marks on the top of the shaft should be aligned
with the gas piping.
•
In the fully closed position, the dash marks on the top of the shaft should be
aligned at a 90° angle across the gas piping.
If the ball valve shaft is not properly aligned or if the manifold pressure does not match
the settings in the chart started below, the ball valve will need to be adjusted.
Manifold Pressure (" w.c.) Measured at the Pressure Tap by the Gas
Transducer - Gas Control Option AG58 or D12G
RDH
Size
RHH/
SHH
Gas
Type
High Setting
100% on ModHeat
Low Setting
0% on ModHeat
175 130
Natural 3.4 0.15
Propane 10.0 0.30
(continued)