Table of Contents
The trailer hand valve (also referred to as the trolley valve or Johnson bar) is a mechanism that works the trailer brakes. It should only be used to test the brakes. Using it while the vehicle is being driven could cause a skid.
When should a trolley valve be used?
The trolley valve, or trailer hand valve or Johnson bar, operates the trailer brakes on a combination vehicle. The trolley valve should only be used when testing the tailor brakes, and should never be used while driving. If you use the trailer hand brake while driving, you can cause the tailor to skid.
What is the purpose of the trailer supply valve?
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. The tractor protection valve prevents air loss from the towing vehicle.
What is a emergency relay valve?
The relay emergency valve controls the air brake system of a trailer and provides the “emergency brake function”. Versions with a predominance device can adapt the braking effect between towing and towed vehicle.
Why you should not use the trailer hand valve?
Trailer Hand Valve Do not use it in driving because of the danger of making the trailer skid. The foot brake sends air to all the brakes on the vehicle (including the trailer(s). There is much less danger of causing a skid or jackknife when using just the foot brake.
What should you hook up before backing under the trailer?
After connecting the air lines but before backing under the trailer you should: A Supply air to the trailer system, then pull out the air supply knob.
At what pressure will the protection valve for your trailer pop out?
You push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes. The valve will pop out (thus closing the tractor protection valve) when the air pressure drops into the range of 20 to 45 psi.
What color is trailer valve?
The trailer supply valve (usually a red octagonal button) is mounted in the cab of the vehicle, easily accessible to the driver. You open the valve by pushing or pulling the button, depending on the type used. Note: The trailer-supply valve has also been referred to as the emergency valve.
What does the blue glad hand do?
A gladhand connector or gladhand coupler is an interlocking hose coupling fitted to hoses supplying pressurized air from a tractor unit to air brakes on a semi-trailer, or from a locomotive to railway air brakes on railroad cars.
What is the name of the valve that supplies trailer with air?
6.2. Shut-off valves (also called cut-out cocks) are used in the service and supply air lines at the back of trailers used to tow other trailers. These valves permit closing the air lines off when another trailer is not being towed.
Where is relay valve located?
To correct this condition on a long-wheel-base vehicle, a relay valve is installed near the rear service brake chambers.
What is quick release valve?
The function of a quick-release valve (Fig. 23) is to rapidly exhaust air from the controlled device. It is normally located adjacent to the controlled device, rather than requiring exhaust air to return and exhaust through the control valve.
What is the purpose of the relay emergency valve and where is it fitted?
The relay emergency valve (fig. 7-53) acts as a relay station to speed up the application and release of trailer brakes. It automatically applies the trailer brakes when the emergency line of the trailer is broken, disconnected, or otherwise vented to the atmosphere if the trailer air brake system is charged.
What trailer off tracks the most?
Longer vehicles will offtrack more. The rear wheels of the powered unit (truck or tractor) will offtrack some, and the rear wheels of the trailer will offtrack even more. Steer the front end wide enough around a corner so the rear end does not run over the curb, pedestrians, other vehicles, etc.
What might happen if the trailer is too high?
What might happen if the trailer is too high when you try to couple? It may not couple correctly. After coupling, how much space should be between the upper and the lower fifth wheel? You should look into the back of the fifth wheel to see if it is locked onto the kingpin.
Why would you never use the trailer handbrake to straighten out a jackknifing trailer?
Why should you not use the trailer hand brake to straighten out a jackknifing trailer? Because the brake handle is too hard to reach. Because the brakes on the trailer wheels cause the skid in the first place. Because the brakes on the trailer wheels will not respond to the hand brake.
What will happen if the airlines are crossed when you hook up an old trailer?
A If the trailer has no spring brakes, you could drive away but you would not have trailer brakes. “If you crossed the air lines, you could drive away but you wouldn’t have trailer brakes.
Why should you lock glad hands together?
This will prevent water and dirt from getting into the coupler and the air lines. Use the dummy couplers when the air lines are not connected to a trailer. If there are no dummy couplers, the glad hands can sometimes be locked together (depending on the couplings). It is very important to keep the air supply clean.
What will happen if the air lines are crossed when you hook up to an older trailer before 1975 ):?
The driver crosses the air lines when hooking up to an old trailer. A If the trailer has no spring brakes, you can drive away, but you will not have trailer brakes. B The brake pedal will work the trailer spring brakes instead of the air brakes.
Why do many trailers built before 1975 have no parking brakes?
You could drive away, but have no trailer brakes. Why do many trailers built before 1975 have no parking brakes? They don’t have spring brakes. If the service air line comes apart while driving but the emergency line is okay, what happens immediately?.
Why must the fifth wheel plate have enough grease?
Grease can build up on the fifth wheel and attract dirt and debris, so degreasing it prior to inspecting it allows you to see any potential damage more easily. It is also very important to make sure all the grease buildup is removed in and around the lock jaw, throat and pivot points.
