The inlet gas supply pressure of 10.5 inches w.c. is the increased gas supply pressure that was used in the CSA International testing of the product. The individual gas valves, regulators and pressure switches are rated by the component manufacturer to withstand a maximum supply pressure of 14 inches w.c. As long as the maximum incoming gas supply pressure does not exceed the 14 inches w.c. or ½ psi of pressure you will not void the unit’s warranty.
A drop in gas supply pressure indicates excessive pressure drop in the gas supply piping system. This pressure drop may be caused by frictional losses from excessive length of pipe or an excessive number of fittings in the pipe system. Pressure drop can also be caused by regulators or gas meters that are marginally or improperly sized to deliver the volume of gas required to allow the unit to fire at full rate manifold pressure.
Each water heater or boiler produced by Lochinvar is equipped with an internal gas pressure regulator. When a high gas pressure service (gas pressure in excess of ½ pound of service pressure) is installed to the unit, an additional regulator must be supplied to reduce the inlet gas pressure. High gas pressure is typically a 2 psi system. The external regulator should be installed six to ten linear feet from the gas inlet to the water heater or boiler. This provides a sufficient reservoir between the two regulators to keep each regulator from constantly responding to the action of the other regulator. This is typically seen as a constantly varying inlet gas pressure. This occurs when the external opens to supply gas to the appliance regulator, the appliance regulator sees the surge of pressure and closed down to maintain the reduced pressure to the manifold, as the manifold supply pressure decreases the external regulator decreases its output. As the appliance regulator see the reduction in supply pressure it opens to try to maintain the specified manifold pressure. When the two regulators are installed in close proximity in the piping they will continue to open and close causing a hunting to continuously vary gas supply pressure. A longer section of pipe installed between the regulators will allow a larger volume of gas to be maintained between the regulators. This will allow each regulator to react with a slower smoother reaction to the volume demands of a gas appliance.
A referenced gas valve allows the gas output from the regulator to vary as the output of the combustion air fan varies. Many conditions such as voltage, draft, wind, equipment room pressures, etc. can change the output pressure of the combustion air fan. A referenced gas valve will automatically vary the gas supply to balance the changes in combustion air. This ensures a reliable clean combustion process and eliminates nuisances flame failure problems due to job site related conditions.
A lock-up type regulator will prevent an upward creep in gas pressure in the off cycle. A non-lock-up type regulator may allow the static gas pressure to creep upward to a pressure greater than the maximum rated inlet pressure for the valve or regulator. This can damage the component or result in a catastrophic failure of the gas valve.
A small ¼ inch diameter line can supply pressure but as soon as the gas valve opens the diameter of the pipe must be able to provide the proper volume of gas required to fire the burners at the desired rate. If the volume is restricted due to pipe size, regulator sizing or meter sizing, the burners can not fire at full rate. This can result in nuisance flame failures and other operational problems.
A biased gas valve references the gas manifold pressure to the outlet pressure of the combustion air fan. When ever there is a variation in the fan output, the gas output from the biased gas valve responds accordingly to prevent nuisance flame failure or operational problems.
When ever the gas supply pressure to the water heater or boiler exceeds ½ pound or 14 inches w.c. of gas pressure a secondary regulator of the lock-up type must be used. It is very common for the gas utility to supply a 2 psi service from the meter. This would require a pounds to inches regulator to reduce the pressure to 14 inches w.c. before the gas goes to the appliance.
The gas supply tables used by Lochinvar and the National Fuel Gas Code are based on a 0.5 inch pressure drop. As long as a pressure drop of no more than one inch is observed, the water heater or boiler will usually operate without a nuisance flame failure problems or cycling on startup. If at any time the gas supply pressure drops below the minimum required pressure it indicates that there is a volume problem and the possibility for nuisance operational problems based on gas supply.
LP gas is supplied as a liquid in a tank. This liquid must vaporize to a gas before it can be used by the water heater or boiler. Each size LP tank has a certain vaporization capacity based on the fill of the tank and the ambient temperature where the tank is installed. In cold northern climates the low temperatures may severely restrict the tanks ability to convert the liquid to a gas in an adequate volume to sustain the combustion process. When this occurs, a vaporizer is used to preheat the LP to ensure that it is converted to a gas. Icing on the gas line and/or regulator out of the LP gas tank is an indicator that the LP is not properly vaporizing. Consult with your local LP supplier to properly size a vaporizer.
Many of these flexible gas line connections have a significant reduction in internal diameter and can result in a restriction in the volume of gas required for combustion in a large commercial gas water heater or boiler. These flexible gas lines are typically used on residential water heaters, furnaces, residential ranges and dryers. The use of flexible gas lines on high Btu/hr input commercial gas equipment can result in nuisance operational problems and is not recommended.
The individual gas valves, regulators and pressure switches are rated by the component manufacturer to withstand a maximum supply pressure of 14 inches w.c. or ½ psi gas pressure. As long as the maximum incoming gas supply pressure does not exceed the 14 inches w.c. of pressure you will not damage the internal components of the gas train.
Lochinvar does not recommend the use of flexible gas connectors when installing gas supply piping to our commercial products. Flexible gas connections are typically used on residential water heaters, residential furnaces and gas ranges. A flexible gas connector can provide a significant reduction in the internal diameter of the gas supply piping to a commercial appliance. This can reduce the required volume of gas needed to ensure the ability of the appliance to fire at full input rate. When the volume of gas is reduced to a fan assisted unit it may result in nuisance flame failure problems or nuisance operational on off cycles.
The gas authority is providing 2 psi after the meter. If the gas supply piping to the unit exceeds ½ psi/14 inches w.c, a secondary gas pressure regulator of the full lock-up type must be installed in the gas supply piping to the unit. This regulator must reduce the incoming 2 psi of gas pressure to within the minimum and maximum pressure specified on the unit’s rating plate.
An external gas pressure regulator must be installed six to ten linear feet from the gas inlet to the water heater or boiler. This provides a sufficient reservoir in the piping between the two regulators to keep each regulator from constantly responding to the action of the other regulator. If a regulator is installed to close to the unit’s internal regulator, it will typically respond by a constantly varying inlet gas pressure with every change in the internal gas regulator and cause nuisance operational problems.
The gas pressure regulator works by placing a load on the diaphragm with a spring to control the opening of the regulator based on pressure. Atmospheric gas fired units achieve all adjustment to gas supply pressure by the manual adjustment of the spring in the regulator. A referenced gas valve is used on the fan assisted Lochinvar commercial products. A referenced gas valve uses a combination of the manual spring adjustment and air pressure from the combustion air fan to set the output pressure from the regulator in the gas valve. The spring will supply from 1.4 inches to 1.8 inches of mechanical preload on the regulators diaphragm. Additional pressure from the fans discharge pressure is placed on the diaphragm. The spring pressure plus the air pressure from the fan combine for the gross manifold pressure to the burners.
The gas pressure is still above the minimum pressure listed on your label. Lochinvar units use fan assisted combustion, delivering air in a fixed volume. When the volume of gas required is decreased it can lean the combustion process where the flame can not be sensed. This results in a flame failure condition. A unit with a referenced gas valve is more tolerant to variations in gas pressure within some limits. Many times you may experience a flame failure but the movement of the gas manometer indicates that the gas pressure only reached the minimum required for operation. This is because the movement of the water column in the manometer has a lag between the actual drop in pressure and the time that it takes to show the indicated change. The change in pressure is not sustained for an extended period of time and the manometer will not give an instantaneous indication of the change in pressure. A properly calibrated magnahelic will usually show these quick response changes in gas supply pressure more readily than a basic manometer. This is seen by the extreme swings in the indicating needle on the pressure scale.
The gas line connection to the unit is based on the sizing of the internal gas valves and regulator to maintain less than a one inch pressure drop inside of the unit. It is entirely possible that the distance from the gas meter to the appliance will require a larger gas line than the gas connection to the appliance. The larger gas line is required to compensate for frictional losses in the pipe as the gas is carried from the meter to the appliance. This is true for all manufacturers.
The information supplied on the unit’s rating plate is specified by the ANSI Standard. The 10.5 inches maximum is the maximum supply pressure that the unit was tested to per the ANSI Standard for natural gas. The individual components that are used in the gas train are rated for a maximum inlet pressure of 14 inches w.c or ½ psi of gas. As long as gas supply pressures do not exceed the 14 inches w.c or ½ psi there will be no damage to the gas train components.
Excessive gas supply pressure can either lock the gas vale or regulator in a closed position or, in the case of extremely high gas pressure; it may override the gas valve, damage the diaphragm and allow unrestricted gas flow to the burners. Extremely high gas pressure can result in a catastrophic failure of the equipment.
Lochinvar water heaters and boilers can be supplied with orifice sizing to operate on propane air mixtures. We must know the Btu per cubic foot and specific gravity of the propane air mixture to provide proper orificing for clean combustion. The owners of the equipment must carefully monitor the propane air mixing equipment to ensure a consistent gas quality. Many times a propane air system will tend to run rich and have a high Btu/ft3 that results in sooting or operational problems.
This is an indication of a volume problem in the gas supply. Review the gas pipe sizing to the National Fuel Gas Code tables, review the regulator sizing and review the sizing of the gas meter. 80% of all water heater and boiler sales are replacement and many times a larger unit is installed without regard for the need to increase in pipe size, regulator sizing or gas meter sizing as the Btu/hr is increased or additional load is placed on the system.
As the gas supplied to the inlet of the water heater or boiler flows into the gas train there is a pressure drop. Typically this pressure drop is one inch water column or less. The minimum inlet pressure is usually equal to the manifold pressure plus the internal pressure drop in the gas train valves, regulator and fittings before the gas is supplied to the burners.
This indicates a volume problem in the gas supply. Review the gas pipe sizing, valves, gas meter sizing and regulator sizing. All must be sized per the National Fuel Gas Code and the component manufacturer’s specifications. Ideally we would not want to see more than one inch of pressure drop between static and operating pressure. In most cases, is the pressured does not drop below the minimum burner operation will be sustained. In some cases when the pressure drops to the minimum, the manometer may not respond fast enough to show an actual drop below the minimum pressure. In this case you may experience nuisance operational problems on ignition at minimum pressure.
No manufacturer can supply internal valves and regulators that will function under these extreme test pressures. The installing contractor is responsible to supply a valve at the point where the gas is supplied to the appliance. This valve must have a sufficient WOG pressure rating to block the gas test pressures and prevent damage to the unit’s internal components when it is in the closed position.
All Lochinvar gas fired appliances must be supplied with a regulator that will prevent gas pressure creep either in the operating cycle or the off cycle that will exceed the maximum rating of the internal gas train components. This is accomplished by installing a lock-up type regulator in the gas supply.
A single gas supply regulator that is properly sized for multiple appliances is acceptable. The key to reliable operation is proper sizing and placement of the regulator in the gas supply piping. Proper installation will typically require 6 to 10 feet of pipe after the regulator and before the first unit to provide a volume of gas to supply the multiple units and prevent variation in gas supply pressure
They are equally important because you need both proper volume and pressure for a gas fired appliance to operate properly.