SECTION 3 - CHASSIS & SCISSOR ARMS
3-62
– JLG Sizzor –
3121133
EPR Assembly
The EPR assembly is a combination Low Pressure Regu-
lator and a Voice Coil Assembly. The Voice coil is an elec-
tronic actuator which is controlled by an internal
microprocessor. The microprocessor provides output data
to the ECM and receives input data over a CAN BUS con-
nection. The internal microprocessor receives electrical
signals from the Fuel Pressure Sensor FPS and the Fuel
Temperature Pressure FTP and communicates the data to
the ECM. The ECM uses the FPS and FTP data to calcu-
late the location of the secondary lever in the LPR and
sends that data back to the EPR via the CAN BUS. The
internal microprocessor in the EPR will then output a sig-
nal, which causes the voice coil to move and position the
secondary lever to the correct location.
Low Pressure Regulator (LPR)
The LPR is a combination vaporizer, pressure regulating
device. The LPR is a negative pressure, two stage regula-
tor that is normally closed when the engine is not running.
When the engine is cranking or running, a partial vacuum
is created in the fuel line which connects the regulator to
the mixer. This partial vacuum opens the regulator permit-
ting fuel to flow to the mixer.
Propane fuel enters the primary port of the LPR and
passes through the primary jet and into the primary/
exchanger chamber. As the propane passes through the
heat exchanger the fuel expands and creates pressure
inside the chamber. The pressure rises as the fuel
expands when the pressure rises above 1.5 psi (10.34
kpa), sufficient pressure is exerted on the primary dia-
phragm to cause the diaphragm plate to pivot and press
against the primary valve pin thus closing off the flow of
fuel. This action causes the flow of fuel into the regulator
to be regulated.
When the engine is cranking, sufficient vacuum will be
introduced into the secondary chamber from the mixer
drawing the secondary diaphragm down onto the spring
loaded lever and opening the secondary valve allowing
vaporized fuel to pass to the mixer. This mechanical action
in conjunction with the EPR reactions causes the down-
ward action on the secondary lever causing it to open
wider allowing more fuel to flow to the mixer.
THE VOICE COIL SECTION OF THE EPR ASSEMBLY IS AN EMIS-
SIONS CONTROL DEVICE AND CANNOT BE REBUILT. IF THE
COIL ASSEMBLY FAILS TO OPERATE PROPERLY, REPLACE IT
WITH AN OEM REPLACEMENT PART ONLY.
1. Pressure Regulator Section
2. Fuel Inlet
3. Coolant Passage
4. Primary Test Port
5. Secondary Test Port
6. Voice Coil Section
Figure 3-29. EPR Assembly
Figure 3-30. Low Pressure Regulators
Property of American Airlines
