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