When the pressure in the supply line reaches 45 psi, the service line port of the tractor protection valve opens. This allows application air pressure to travel down the service line to the trailer when a brake application is made.
What happens when the tractor protection valve closes?
When the tractor protection valve closes, it stops any air from going out of the tractor. It also lets the air out of the trailer emergency line. This causes the trailer emergency brakes to come on, with possible loss of control. (Emergency brakes are covered later.)
At what PSI will the tractor protection valve control knob pop out when performing the air pump down test?
The tractor protection valve and parking brake valve should close (pop out) on a tractor-trailer combination vehicle and the parking brake valve should close (pop out) on other combination and single vehicle types when the air pressure falls to the manufacturer’s specification (20 – 40 psi).
What is another name for the tractor protection valve?
Any truck designed to pull a trailer with air brakes is going to be equipped with tractor protection system, which consists of the tractor protection valve–just to confuse you [CHCUCKLING] the system and the valve are called the same thing – the tractor protection valve and the red, eight-sided trailer air supply …
Which shutoff valves should be open and closed?
All shut-off valves should be open. … When starting a trip, be sure that all shut-off valves are in the open position, except for the last valves on the rear trailer. It is important that air reaches the brakes on all trailers and that the air is not able to escape from the back of the vehicle.
How is the tractor protection valve operation?
A tractor protection valve (Fig. 38) is usually mounted on the cab or chassis of the tractor. When the trailer-supply valve is open, air passes through the bottom of the tractor protection valve and charges the trailer through the supply line (also called the emergency line).
Where are the shut-off valves located on a tractor trailer?
These valves permit closing the air lines off when another trailer is not being towed. You must check that all shut-off valves are in the open position except the ones at the back of the last trailer, which must be closed.
Which vehicle off track the most?
Off-tracking is defined as the different paths taken by the front and rear wheels in a turn. The longer the vehicle, the greater the difference will be. Thus, the wheels on the front trailer will offtrack more than the tractor’s rear wheels, and the wheels on the rearmost trailer will offtrack most of all.
At what PSI do air brakes lock up?
If the pressure in the air system pulls below 60 psi, the parking brake knob will pop out and set the parking brakes. This is a safety feature so the truck will stop, because if the pressure falls too low, the service brakes will not work. The other system component stops the vehicle when you push on the brake pedal.
When spring brakes are on you should never?
Never apply the brake pedal if your spring breaks are activated. Brakes can be damaged if they are subject to both springs and air pressure.
How should you check that your service brakes are working properly?
How should you check that your service brakes are working properly? Wait for normal air pressure, release the parking brake, move the truck forward slowly, and apply the brake pedal firmly. You just studied 70 terms!