Impco HHI, Service Manual

Page: 21 / 485

21
DESCRIPTION AND OPERATION OF THE FUEL
SYSTEMS
LPG FUEL SYSTEM
The primary components of the LPG fuel system
are the Fuel Storage Tank, Electronic Pressure
Regulator (EPR), Fuel Mixer, Throttle Control De-
vice, electric Shut-Off Valve, Engine Control
Module (ECM), Oxygen Sensor and a Catalytic
Converter. The system operates at pressures which
range from 355.60mm (14.0 inches) of water col-
umn up to 21.5 BAR (312 psi).
LPG FUEL TANK
LPG is stored in the fuel tank as a liquid. The ap-
proximate pressure of the fuel in the tank is 8.8 bar
(130 psi) when the tank is full at an ambient tem-
perature of 27° C (81°F). The boiling point,
(temperature at which the liquid fuel becomes va-
por) is approximately 40° C (-40° F). When the fuel
changes from liquid to vapor the fuel expands and
creates pressure inside the tank. When the tank
service valve is opened the pressure inside the
tank forces the liquid fuel out though the pickup
tube located near the bottom of the fuel cylinder.
Because the LPG is stored under pressure the tank
is equipped with a safety valves which are normally
set at 25.8 bar (375 psi) to prevent tank rupture due
to over-pressurization of the cylinder. The service
valve mounted in the end of the cylinder controls
the
flow of fuel from the tank. By turning the handle
to its “open” position, fuel fl ows out of the tank and
into the service line. The service valve is also
equipped with a safety feature called an excess
flow check valve. This feature reduces the flow
from the service valve in the event of a rupture of
the fuel line or any downstream.
Typical LPG Cylinder
1. Liquid Outage Fill Check Valve
2. Pressure Relief Valve
3. Liquid Outage Valve w/quick disconnect coupl-
ing (also referred to as the manual shut-off
valve or MSV).
4. Filler Valve
5. Fuel Gauge
6. Vapor Withdrawal Tube (when applicable)
7. 80% Limiter Tube
8. Fuel Level Float
9. Liquid Withdrawal Tube
SERVICE LINE
LPG flows from the fuel tank to the electric LPG
Shut-Off Valve via the service line. The service
line is connected to the tank utiliz
ing a quick
coupler. The other end of the service line is con-
nected to a bulkhead connector mounted on the
equipment sheet metal. This bulkhead connector
allows for a safe means of passing through the
equipments engine compartment sheet metal and
into the engine compartment. If a bulkhead con-
nector is used a pressure relief device is mounted
in the service line or the connector itself to pre-
vent over pressurization. The service line is
made of high pressure hose with special material
or possibly tubing which is compatible with the
LPG fuel and should always be replaced with an
OEM supplied part.
The bulkhead assembly should never be
removed. Never run a service line through
the sheet metal.