High Altitude Compensation System: Operation: Gas

At high altitudes (above 4000 ft.), fuel supply is decreased in the same proportion as the air density. Normally, the control pressure is regulated by a diaphragm and a spring. To achieve altitude compensation, another diaphragm with a spring and a chamber have been added. See Fig 1 .

Fig 1: Control Pressure Regulator with High Altitude Compensation

The chamber maintains a constant low altitude (below 4000 ft.) pressure while the pressure outside it varies according to altitude. The pressure difference causes the diaphragm to exert more or less pressure on the inner spring.

At increasing altitudes, decreasing pressure outside the diaphragm chamber causes the lower diaphragm to rise. The resulting increase of pressure on the upper diaphragm increases control pressure. This provides a correct air/fuel mixture.