Gaseous Fuel Systems
20 Installation Guidelines for Spark-Ignited Stationary Emergency Generators
5.4.2— Definitions
The following definitions are provided for use in this manual.
5.4.3— Best Practices
These are the manufacturer recommended best practices for configuring and sizing fuel supply piping to generators.
These best practices have been developed specifically for the manufacturer’s product and may not represent conven-
tional gaseous fuel system sizing methods, particularly those used frequently with low volume appliance installations.
Compliance with these best practices will help to ensure the generator set engine will operate properly under dynamic
conditions.
• The minimum distance from the primary pressure regulator outlet to the generator connection point will be cov-
ered in the regulator manufacturer's installation instructions. Do not connect the pressure regulator directly to the
flexible fuel line on the generator. The piping between the primary pressure regulator and the connection point on
the generator acts as a reservoir (accumulator) which stores gas and, therefore, can minimize or maximize the
changes in delivery pressure that the generator sees during cranking and load changes.
Table 5-1. Definitions
Term Description
Allowable Pressure
Drop
The design pressure loss in the system under maximum probable flow conditions, from the point of deliv-
ery to the inlet connection of the generator set, shall be such that the supply pressure at the generator is
greater than or equal to the minimum pressure required by the generator at its full load capacity.
Authority Having
Jurisdiction (AHJ)
(NFPA-54)
An organization, office, or individual responsible for enforcing the requirements of a code or standard, or
for approving equipment, materials, an installation, or a procedure.
Cubic Foot (ft
3
) of
Gas (NFPA-54)
The amount of gas that would occupy 1 ft
3
when at a temperature of 600º F saturated with water vapor
and under a pressure equivalent to 30 in. w.c.
Generator
Connection Point
The connection point for the fuel supply system to the generator set is the end of the manufacturer sup-
plied flexible hose fitting which connects to the fitting on the base frame of the generator. An elbow and
short nipple can be incorporated to allow the flexible hose to be positioned parallel to the unit base frame.
The size of the connection point on the base frame is shown in each unit’s installation drawing; the size of
the flexible hose (and any elbow and nipple) must be equal to or larger than this connection point. The
flexible hose must be installed straight without bending, twisting or kinking.
psi & psig Measure of pressure in pounds per square inch and pounds per square inch gauge.
Inches of Water
Column (in.w.c.)
Measure of pressure in inches of water column (in. w.c.). 14 in. w.c. = approximately 0.5 psi.
Primary Regulator
A pressure regulator installed between the service regulator (NG) or first-stage regulator (LP-Gas vapor)
sized to provide the pressure and volume required by the generator at its full rated load capacity.
Regulator (for LP-Gas vapor)
First-Stage
Regulator
A pressure regulator for LP-Gas vapor service designed to reduce pressure from a container to 10.0 psig
or less.
High-Pressure
Regulator
A pressure regulator for LP-Gas liquid or vapor service designed to reduce pressure from the container to
a lower pressure in excess of 1.0 psig.
Second-Stage
Regulator
A pressure regulator for LP-Gas vapor service designed to reduce first-stage regulator outlet pressure to
14 in. w.c. or less. For generator set purposes, this is also referred to as the Primary Regulator.
Regulator (for NG fuel)
Pressure Regulator Device placed in a gas line for reducing, controlling, and maintaining pressure in downstream piping
Service Regulator
A pressure regulator installed by the servicing gas supplier to reduce and limit the service line gas pres-
sure to delivery pressure.
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