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