By regulation, aircraft fuel systems must be designed with a way to manually stop the flow of fuel to the engine. In some aircraft, this is accomplished by simply installing an on-off valve in line with the engine fuel supply. On others, manual control is provided in conjunction with a selector that allows fuel to be taken from one or both tanks independently (with a few exceptions). In most of the Piper Cherokee series, this function is accomplished by using a brass body that accepts a fuel-supply line from each tank and a brass inner cone drilled to route fuel in the proper direction. It's a simple device with a limited function and maintenance is seldom required. There is, however, one important thing to remember about the Piper fuel valve: Both the inner cone valve and the selector body are made of the same brass material and the sealing between the cone and body is accomplished simply by a precise fit.
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