Generac Power Systems NP Series - Vapor Withdrawal.14; Primary Regulator; Gaseous Carburetion

• Optimum gas pressure at the inlet to the gaseous fuel
solenoid valve and secondary regulator is 11 inches
water column.
• The instaljer’s fuel supply connection point is at the
gaseous fuel solenoid valve. This is a 3/4 inch (female)
connection. Provide a suitable 3/4 inch NPT (male) con¬
nector to attach to the fuel supply line.
• Use a length of approved flexible fuel hose between
gaseous fuel solenoid valve and rigid gas piping. The
flexible line should be at least six (6) inches longer than
necessary.
VAPOR WITHDRAWAL
Liquid propane (LP) gas is stored in pressure tanks
as a liquid. The gas systems used with these genera¬
tors were designed only for “vapor withdrawal” type
systems. Vapor withdrawal systems use the gas
vapors that form above the liquid fuel in the tank. Do
NOT attempt to use the generator with any “liquid
withdrawal" type system.
PRIMARY REGULATOR
Gas pressure delivered to the solenoid valve must be
properly regulated by means of a primary gas regula¬
tor. Mount the primary regulator at the gas tank outlet
or in the supply line from the gas tank. The following
rules apply;
• For best results, the primary regulator supplies gaseous
fuel to the secondary regulator at 11 inches water col¬
umn. Do NOT exceed 14 inches water column.
• The installer must be sure the primary regulator is rated
at sufficient gas flow to operate the generator plus all
other gas appliances in the circiut.
NOTE: Recommended MINIMUM gas flow rate for all
air-cooled NP or Q series generators is 67 cubic feet
per hour.
IMPORTANT: IF AN EXISTING PRIMARY GAS
REGULATOR DOES NOT HAVE A SUFFICIENT
FLOW CAPACITY FOR THE GENERATOR AND
OTHER GAS APPLIANCES IN THE CIRCUIT, (a)
INSTALL A PRIMARY REGULATOR WITH ADE¬
QUATE FLOW RATE, OR (b) INSTALL A SEPA¬
RATE REGULATOR ONLY AND RATED AT LEAST
67 CUBIC FEET PER HOUR. THE INLET SIDE OF
ANY PRIMARY REGULATOR THAT SUPPLIES THE
GENERATOR MUST CONNECT DIRECTLY TO
GAS TANK PRESSURE. DO NOT TEE THE GEN¬
ERATOR LINE INTO A GAS CIRCUIT FEEDING
OTHER AREAS.
GASEOUS CARBURETION
LP gas vapors should be supplied to the secondary
regulator inlet at about 11 inches water column (posi¬
tive pressure). The engine pistons draw air in during
the intake stroke (Figure 20). This air passes through
a carburetor venturi which creates a low pressure that
is proportional to the quantity of air being pumped.
The low pressure from the carburetor venturi acts on
the regulator diaphragm, to pull the diaphragm toward
the source of low pressure. A lever attached to the
diaphraghn opens a valve to permit gas glow through
the carburetor.
The greater the air flow through the carburetor ven¬
turi, the lower the presure at the venturi throat. The
lower the pressure at the venturi throat, the greater
the diaphragm movement and the greater the move¬
ment of the regulator valve. The more the regulator
valve opens, the greater the gas flow that Is propor¬
tional to air flow through the generator.
Figure 20 — Propane Gas Carburetion Diagram
AIR gas at
AREA
— 14 —