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RELIEF VALVE
This unit is supplied with a relief valve(s) sized in accordance with ASME Boiler and Pressure Vessel Code, Section IV (“Heating Boilers”). The relief valve(s) is installed in the vertical position and mounted in the hot water outlet. No valve is to be placed between the relief valve, and the unit. To prevent water damage, the discharge from the relief valve shall be piped to a suitable floor drain for disposal when relief occurs. No reducing couplings or other restrictions shall be installed in the discharge line. The discharge line shall allow complete drainage of the valve and line. Relief valves should be manually operated at least once a year.
CAUTION
Avoid contact with hot discharge water.
NOTE:
The gas train and controls assembly provided on this unit have been tested under the applicable American National Standard to meet minimum safety and performance criteria such as safe lighting, combustion and safety shutdown operation.
air blower. The valve is a 1:1 differential pressure air/gas ratio controller. The valve adjusts the same pressure difference on the gas side as it senses on the air side. The valve performs the functions of safety shutoff, constant pressure regulation and air/gas ratio control. Slow opening and safety shutoff is accomplished by operation of an electro hydraulic cylinder. Full closing of the valve seat occurs in less than 0.8 seconds when the valve is
The manifold pressure is preset at the factory and adjustment is not usually required if gas supply pressure is maintained within the specified range. If the manifold pressure is to be measured, follow the “Gas Manifold Pressure Measurement Procedure” for proper measurement.
There are no serviceable parts on the ratio gas valve actuator.
DIAPHRAGM GAS VALVE
RATIO GAS VALVE
FIG. 43 Ratio Gas Valve
The main gas valve supplying gas to the burner on this appliance utilizes a pressure regulating electro hydraulic actuator providing a slow opening, fast closing safety shut off and air/gas ratio control for the gas combustion process. This gas valve controls the pressure difference across the restriction in the gas supply line as a function of the pressure difference across the combustion air supply to the burner. The actuator maintains a constant air to gas ratio as the volume of air changes based on the operation of the combustion
FIG. 44 Diaphragm Gas Valve
A diaphragm type gas valve is also provided in the gas train. As the second valve seat in the gas train, it supplies a redundant safety shutoff valve seat in the gas supply to the burner to ensure safe operation in the remote event of a gas valve failure. The diaphragm gas valve is energized with 24 VAC power at the same time the ratio gas valve is powered in the operational sequence to ignite the burner.
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