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What is the trailer hand valve?
The trailer hand valve is used to apply the trailer service brakes independent of the towing vehicle’s brakes. The trailer supply valve is usually a push/pull type valve near the driver that supplies air to the trailer’s brake system through the supply line.
What is another name for the trailer hand valve?
The trailer hand valve (also called the “trolley valve” or “Johnson bar”) works the trailer brakes. The trailer hand valve should be used only to test the trailer brakes.
Where is the hand valve on a towing vehicle?
Often, a hand valve is also fitted on the steering column or the instrument panel of the towing vehicle so the driver can apply the trailer service brakes independent of the towing vehicle’s brakes. When the hand valve and brake pedal are used at the same time, the trailer will receive the higher pressure.
What is the hand control valve on a trailer?
Trailer hand-control valve. The hand valve, or “spike” (Fig. 39) is added so that you can apply the trailer’s brakes independent of the tractor. The hand valve is typically supplied from primary and secondary circuits and plumbed to a double-check valve (which is also fed from the foot valve).
Where is the air supply valve on a trailer?
The trailer supply valve is usually a push/pull type valve near the driver that supplies air to the trailer’s brake system through the supply line (See Diagram 5-3). This valve normally has a red, eight-sided knob that the driver pushes in to open and supply air to the trailer and pulls out to close or when no trailer is attached.
What can a hand control valve do for a tractor?
Trailer hand-control valve Independent operation of the trailer brakes has two common uses: To couple or uncouple the trailer. In the event that the tractor goes into a skid, gentle brake applications using the hand valve may be of some use in trying to straighten out the unit (never apply the hand valve if the trailer goes into a skid).