Doosan G20P-5, Service Manual, Page: 158 / 306

G424F(FE) Service Manual Chapter 5. Engine Management System (EMS) 156
stage) valve closes. Unlike most other
regulator/converters, the N-2001 primary valve
closes with fuel pressure rather than against
pressure, extending primary seat life and adding
additional safety.
Figure 4. N-2001 Regulator
Liquid propane must be converted into a gaseous
form in order to be used as a fuel for the engine.
When the regulator receives the desired vacuum
signal it allows propane to flow to the mixer. As the
propane flows through the regulator the pressure is
reduced in two stages from tank pressure to slightly
less than atmospheric pressure. As the pressure of
the propane is reduced the liquid propane vaporizes
and refrigeration occurs inside the regulator due to
the large temperature drop inside the regulator from
the vaporization of liquid propane. To replace heat
lost to vaporization, engine coolant is supplied by
the engine driven water pump and pumped through
the regulator. Heat provided by this coolant is
transferred through to the fuel vaporization chamber.
Figure 5 shows the heat chamber and the coolant
passage in the N-2001 regulator.
Figure 5. Heat Chamber and Coolant Passage
N-2001 Operation
Refer to Figure 6.
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 closed 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 (10.342 kPa 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.
Figure 6. Parts View of N-2001 Regulator
Since the fuel pressure has been reduced from tank
pressure to 1.5 psi (10.342 kPa) 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