What is the main purpose of the tractor protection valve?

The purpose of the Tractor Protection valve is to protect the tractor air brake system in the event of a trailer breakaway or severe air leak. They are also used to shut off air to the trailer before disconnecting the lines.

What is the main 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.

When the tractor protection valve is opened it allows air to?

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.

At what pressure must the tractor protection valve operate to pass inspection?

Between approximately 20-40 PSI on a tractor-trailer combination vehicle, the tractor protection valve and parking brake valve should close (pop out). On other combination vehicle types and single vehicle types, the parking brake valve should close (pop out).

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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.

Which shutoff valves should be open and closed?

If you’re only pulling one trailer, the shut off valves should always be closed or else the air will simply escape out the back of the trailer. If you’re pulling more than one trailer, all valves should be open except the very last trailer, which should have all valves in the closed position.

How can a driver control the trailer brakes independently?

How can a driver control the trailer brakes independently? The purpose of the trailer brake hand valve (30) is to allow the driver to control independently the amount of application air pressure to be directed to the trailer brakes.

What is a DD3 safety actuator?

DD3 brake chamber

This type of chamber is called a DD3 Safety Actuator. … Internally, these chambers have a mechanical means of locking a brake in the applied position. A control valve similar to the one used in conventional spring brake systems applies the emergency and parking brakes.

When should the trailer hand valve be used?

The trailer hand valve should be used only to test the trailer brakes. 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.

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How does pressure protection valve work?

This serves to allow a build up of air pressure in the system before it is allowed to become available to an accessory such as an air suspension. … When the pressure on the supply side falls the valve closes to preserve some amount of air pressure on the delivery side of the valve.

What will occur if the supply line ruptures?

Rupture of the service line will result in the escape of air pressure, if the brake application is held long enough to cause enough loss of pressure in the tractor system. This pressure drop causes the tractor protection system to close off, exhausting the supply line to the trailer.

What color is the tractor protection valve?

The TPV is also called a ‘towing vehicle’ protection valve. The TSV has a red colored, eight-sided knob and is controlled by the driver.

What is the blue air brake button for?

The yellow one controls brakes on all axles, the red is only for trailer, and the blue is only for the truck unit.

What is the maximum air loss rate for a tractor and trailer?

Air loss rate should be less than 3 psi in 1 minute for a single vehicle. Air loss rate should be less than 4 psi in 1 minute for combination vehicles (vehicles with a trailer).