TP-6694 6/22 85
3.6.4 Fuel System Changeover Kits (Dual Fuel)
A changeover fuel system kit provides automatic changeover from natural gas to LPG vapor. The primary and backup fuels each
have a fuel solenoid valve. The primary fuel is natural gas; the backup fuel is LPG vapor. Before starting, both fuel solenoid
valves are closed. When the generator set starts, the primary fuel solenoid valve opens. The primary fuel line has a pressure
switch in series with a relay connected to the start/run circuit.
When the primary fuel pressure drops below 0.6 kPa (1.4 oz./in.2) or 6.4 cm (2.5 in.) water column, a relay opens the backup
fuel solenoid valve and closes the primary fuel solenoid valve. When the primary fuel pressure rises above 0.6 kPa (1.4 oz./in.2)
or 6.4 cm (2.5 in.) water column, the generator set uses the primary fuel. Contact an authorized service distributor/dealer for kit
availability.
Emissions certified models use a single electronic-controlled pressure regulator (EPR) or direct acting electronic pressure
regulator (DEPR) for both fuels. A tee fitting connects both fuels together upstream of the EPR or DEPR. During operation when
using the secondary fuel, it is normal for a small amount of secondary fuel to seep back through the primary fuel solenoid valve.
To counter this situation, one of two methods is used depending upon the generator set model: (1) a second solenoid valve
(identical to the primary fuel solenoid valve) is installed in a reverse configuration on the primary fuel side or (2) a small vent line
is installed between the primary fuel inlet and the air intake through a fuel solenoid valve.
Dual-fuel systems that include a fuel reset box allow an operator to switch back to the primary fuel. The system will change
automatically to the primary fuel when the secondary source runs low or when the generator set stops and restarts.
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