Vacuum delay valve

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A vacuum delay valve is a valve with a small orifice, which delays a vacuum signal. These are commonly used in automobiles to alter the behavior of vacuum switches, vacuum motors, and other vacuum devices.

The engine in a common automobile produces almost 20 inches of mercury (68 kPa) of vacuum, and this pressure differential has been utilized for everything from automatic locks and windshield wipers to operating emissions control items.

Engine vacuum is also the best direct source of information on the engine's load.

Most delay valves have a one-way function, where there is either no restriction or no movement in one direction.

Delay valves are usually color-coded to their function.[1]

Color Code Time (seconds) Threshold (+/- seconds) Direction
Orange Black 2 0.5 Forward
Purple Black 4 0.8 Forward
Gray Black 10 2 Forward
Brown Black 20 4 Forward
White Black 63.5 13.5 Forward
Yellow Black 100 20 Forward
Green Black 200 40 Forward
Orange White 2 0.5 Reverse
Purple White 4 0.8 Reverse
Gray White 10 2 Reverse
Gold White 15 3 Reverse
Brown White 20 4 Reverse
Yellow White 100 20 Reverse
Red White 375 75 Reverse


  1. ^ "1988 Jeep Cherokee Technical Service Manual.", "Spark Control System." Chrysler, 1987.