PAD AS 7T4798 - Caterpillar

For this application, the high-pressure gas carburetor is used on engines that are turbocharged.
Illustration 1 g01948136
Cross section of the high-pressure gas carburetor
(1) Diaphragm
(2) Sensing holes
(3) Spring
(4) Fuel valve
(5) Chamber
(6) Air horn
(7) Ring
(8) Outer chamber
(9) Fuel outlet port
(10) Inner chamber
(11) Fuel inlet port
(12) Idle adjustment
(13) Butterfly valve for emission control
(14) Throttle plate
(15) Connection for the balance line Air flows into the carburetor through air horn (6). The air fills outer chamber (8). When diaphragm (1) moves away from ring (7) as a result of engine vacuum, the air flows into inner chamber (10) (mixing chamber).Fuel flows into the carburetor through fuel inlet (11). The fuel then flows by the butterfly valve for emission control (13) into the center of the carburetor and into fuel outlet port (9). Fuel valve (4) is fastened to diaphragm (1). When the diaphragm is moved away from ring (7), the fuel flows through fuel valve (4) into inner chamber (10). The fuel is mixed with the fresh air that is entering the inner chamber through the air horn. The air/fuel mixture flows through throttle plate (14) into the inlet manifold.When the engine is stopped, spring (3) holds the diaphragm against ring (7). In this position the fuel valve closed. No air or fuel can enter the inner chamber. When the engine is started, a vacuum in the cylinders is created by the intake strokes of the pistons. A low pressure is created in the inner chamber. This low pressure is felt in chamber (5) behind the diaphragm through holes (2). The pressure in becomes balanced between the two chambers. When the inlet pressure on the diaphragm becomes higher than the spring force, the diaphragm begins to move.As the diaphragm is pushed by inlet pressure, the fuel valve moves. As the fuel valve moves, the fuel outlet port is opened. The air/fuel mixture is allowed to enter the inner chamber. A small volume of air is also measured into the inner chamber. This small volume of air is entered through the opening for idle adjustment (12).When the engine is operating at a constant load and speed, the position of the diaphragm is constant. The diaphragm only moves when the demand for fuel varies.