SPOOL 2381892 - Caterpillar

Illustration 1 g00520949
Typical Fuel Ratio Control (FRC) (A) Inlet air chamber (B) Oil chamber (1) Bolt (2) Diaphragm (3) Spring (4) Piston (5) Valve (6) Valve body (7) Pin (8) Oil passage (9) Spring (10) Governor linkageThe hydrapneumatic FRC is used on turbocharged engines to control smoke during acceleration at low boost.The hydrapneumatic FRC operates on boost pressure from the inlet manifold and oil pressure from the engine. Valve body (6) will not move until inlet manifold pressure increases enough to move valve (5). When the governor control is moved to increase fuel to the engine, valve body (6) limits the movement of internal governor linkage (10) in the fuel on direction. The oil pressure in the oil chamber resists movement of valve body (6) until air pressure increases.As the air pressure increases in inlet air chamber (A), diaphragm (2) and valve (5) move to the right. The valve opens oil passage (8) and the oil in the oil chamber flows to a drain passage. This reduces the oil pressure behind piston (4). Then, spring (3) moves the piston and valve body (6) to the right until oil passage (8) is restricted by valve (5). This permits governor linkage (10) to move further in the fuel on direction.As the air pressure decreases in inlet air chamber (A), diaphragm (2) and valve (5) move to the left. The valve closes oil passage (8) and oil pressure in the oil chamber increases. When the oil pressure increases behind piston (4), spring (3) is compressed and valve body (6) moves to the left. Governor linkage (10) is then limited to a position of less fuel on.During engine start-up, before oil pressure is present in the oil chamber, spring (9) is used to ensure that piston (4) remains against valve body (6). After engine start-up, oil pressure keeps piston (4) against valve body (6). Pin (7) is used to limit the travel of valve body (6) due to the spring force of spring (3) .In order to deliver more fuel to the engine during start-up, some governors that use the hydrapneumatic FRC do not contain pin (7). This allows the rack to advance beyond the FRC limit before the engine is started. The FRC that contains pin (7) and the FRC that does not contain pin (7) operates identically after the engine is running and the oil pressure increases. This feature is known as the pinless FRC and it provides overfueling for easier starting.