MI-04 N-CA55-500TR Mixer Vapor propane fuel is supplied to the N-CA55-500TR mixer by the N-2001 pressure regulator/converter. The N-CA55-500TR mixer uses a piston type air valve assembly to operate a gas-metering valve inside the mixer. The gas-metering valve is normally closed, requiring a negative pressure (vacuum) signal from a cranking or running engine to open. This is the third of the three safety locks in the MI-04 system. If the engine stops or is turned off, the air valve assembly closes the gas-metering valve, stopping fuel flow past the mixer. The gas-metering valve controls the amount of fuel to be mixed with the incoming air at the proper ratio.
The air/fuel mixture then travels past the throttle, through the intake manifold and into the engine cylinders where it is compressed, ignited and burned. (Figure 16) shows the N-CA55-500TR mixer installed with the electronic throttle. N-CA55-500-TR Air/Fuel Mixer Theory of Operation The air/fuel mixer is mounted in the intake air stream between the air cleaner and the throttle. The design of the main body incorporates a cylindrical bore or mixer bore, fuel inlet (1) and a gas discharge jet (2).
In the center of the main body is the air valve assembly, which is made up of the piston air valve (3), the gas-metering valve (4), and air valve sealing ring (5), air valve spring (6) and the check valve plate (7). The gas-metering valve is permanently mounted to the piston air valve with a face seal mounted between the two parts. When the engine is not running this face seal creates a seal against the gas discharge jet, preventing fuel flow with the aid (upward force) of the air valve spring. The outer surface of the piston air valve forms the venturi section of the mixer while the inner portion of the piston is hollow and forms the air valve vacuum chamber.
The check valve plate seals off the bottom of the air valve vacuum (AVV) chamber and the air valve sealing ring seals the top portion of the AVV chamber as the piston moves against the air valve spring. 1 4 3 6 2 5 7 Figure 17 View of Venturi Air Valve Piston Air Intake Gas-Metering Valve open Figure 18 Figure 16 G420E/G424E Tier LP Engine System Operational Overview 20