G420E/G424E
Tier
LP Engine
System Operational Overview
19
N-2001 Theory of Operation
Liquid propane, at tank pressure, enters the N-2001
through the fuel inlet port (1). Propane liquid then
flows through the primary valve (2). The primary valve
located at the inlet of the expansion chamber (3), is
controlled by the primary diaphragm (4), which reacts
to vapor pressure inside the expansion chamber. Two
springs are used to apply force on the primary
diaphragm in the primary diaphragm chamber (5),
keeping the primary valve open when no fuel
pressure is present.
A small port connects the expansion chamber to the
primary diaphragm chamber. At the outlet of the
expansion chamber is the secondary valve (6). The
secondary valve is held close by the secondary
spring on the secondary valve lever (7). The
secondary diaphragm controls the secondary lever.
When the pressure in the expansion chamber
reaches 1.5 psi it causes a pressure/force imbalance
across the primary diaphragm (8). This force is
greater than the primary diaphragm spring pressure
and will cause the diaphragm to close the primary
valve.
Since the fuel pressure has been reduced from tank
pressure to 1.5 psi the liquid propane vaporizes. As
the propane vaporizes it takes on heat from the
expansion chamber. This heat is replaced by engine
coolant, which is pumped through the coolant
passage of the regulator. At this point vapor propane
will not flow past the expansion chamber of the
regulator until the secondary valve is opened. To
open the secondary valve a negative pressure signal
must be received from the air/fuel mixer. When the
engine is cranking or running a negative pressure
signal (vacuum) travels through the vapor fuel outlet
connection of the regulator (9), which is the regulator
secondary chamber, and the vapor fuel inlet of the
mixer. The negative pressure in the secondary
chamber causes a pressure/force imbalance on the
secondary diaphragm, which overcomes the
secondary spring force, opening the secondary valve
and allowing vapor propane to flow out of the
expansion chamber, through the secondary chamber
to the mixer.
Because vapor propane has now left the expansion
chamber, the pressure in the chamber will drop,
causing the primary diaphragm spring force to re-
open the primary valve allowing liquid propane to
enter the regulator, and the entire process starts
again. This creates a balanced condition between the
primary and secondary chambers allowing for a
constant flow of fuel to the mixer as long as the
demand from the engine is present. The fuel flow is
maintained at a constant output pressure, due to the
calibrated secondary spring. The amount of fuel
flowing will vary depending on how far the secondary
valve opens in response to the negative pressure
signal generated by the air/fuel mixer. The strength of
that negative pressure signal developed by the mixer
is directly related to the amount of air flowing through
the mixer into the engine. With this process, the
larger the quantity of air flowing into the engine, the
larger the amount of fuel flowing to the mixer.
Figure 15
N-2001
Cutaway View
7
6
4
1
3
9
5
8
2
