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The required fuel pressure to the unit is measured before the fuel shutoff solenoids at the inlet to the unit
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mounted regulator. A 1/8 inch pipe port in the pressure regulator body, or in the piping just before the pressure
regulator, is provided for this purpose. See Subsection 5.6.1.
Seasonal supply pressure changes to the primary pressure regulator can affect the proper operation of the gen-
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erator. The fuel supply pressure to the unit must remain within the specified operating parameters as stated in
the unit specification sheet. Contact the local utility to find out what can be done to correct seasonal changes.
Use sediment traps.
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The generator set must have its own dedicated fuel supply. Do not connect any other loads to the outlet of the
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primary pressure regulator.
For LP-Vapor systems, due to the nature of the conversion process from LP liquid to LP vapor, consider the following:
The vaporization rate of a given LP tank is dependent on the liquid level in the tank (wetted surface area), the
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ambient temperature around the tank, and relative humidity.
When ambient temperatures are below 40º F, engine fuel consumption is high, and sufficient humidity is present,
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condensation can occur resulting in frosting of the tank at the liquid level. This condition can lead to a reduced
rate of vaporization. See the LP tank sizing section for more information.
5.4.4— Operating Fuel Pressure
The unit specification sheet lists the operating fuel pressure range, as well as the 100% load fuel consumption rate.
The pressure range is the minimum and maximum acceptable pressures for proper operation of the unit under all oper-
ating conditions. The maximum fuel system pressure drop at each condition, that is, static, cranking, running at no
load, and running at full load, is 1-2 in. w.c. as measured at the primary fuel pressure regulator. For definitions of each
condition, see Subsection 5.6.2.
5.4.5— Engine Fuel Consumption
The volume of gaseous fuel consumed at various loads is listed in the unit specification sheet. Both Natural Gas and
LP-Vapor values are provided in Cubic Feet per Hour (CFH). International units of measure are also provided.
Use the following formulas if it becomes necessary to convert CFH to BTUs per Hour:
Natural Gas: CFH x 1000 = BTU per hour
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5.4.6— Fuel Pressure Regulator Sizing
Fuel pressure regulators are designed to automatically adjust flow to meet downstream demand at a required pres-
sure. The typical regulator installed as the primary regulator for a generator set is of the direct acting, internally regis-
tered design. Direct acting means that the pressure sensing element acts directly to open the valve and control the flow
to the load while maintaining the desired pressure.The pressure sensing element is typically a diaphragm which is
opposed by a combination of spring pressure and atmospheric pressure. The valve is the restricting element and con-
sists of some type of variable restriction (cone, poppet, disc) which closes against a fixed seat. Internal registration
means that the pressure used for sensing comes from within the valve body, usually through a passage from the sec-
ondary side (outlet) to the sensing diaphragm.
The primary regulator must be sized to provide the required flow at the rated pressure to the generator at its full load
capacity. The generator fuel consumption values and required operating pressures are listed in the unit specification
sheet.
The manufacturer recommends that the primary pressure regulator be sized for at least 110% of the generator's
required fuel consumption at 100% load, and that the regulator provide no more than a 1-2 inch w.c. pressure drop at
each operating condition, that is, static, cranking, running at no load, and running at full load.
Various regulator manufacturers provide sizing tables, flow capacity, pressure drop tables, and distributors who will
help size a regulator correctly to a system.
Installation Guidelines for Spark-Ignited Stationary Emergency Generators
LP-Vapor: CFH x 2520 = BTU per hour
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Gaseous Fuel Systems
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