A Bad Air Brake Relay ValveBad Tractor Protection ValveBad Spring Brake ValveWrongly Matched Trailer LinesDamaged Metal Trailer Couplers

A trailer emergency supply line carries air to fill the trailer’s tanks. These lines deliver the air pressure used to operate trailer brakes.

You are watching: Why is air backfeeding from my trailer emergency supply line?

Also described as supply or emergency lines, these lines must be defended in order to work-related successfully. If not, they might compromise your trailer as soon as it involves braking.


So, if you alert that air is back-feeding from your trailer emergency supply lines, you need to detect the issue and diagnose it as shortly as feasible. In this article, we’re going to pinpoint why air is back-feeding from your trailer emergency line and what to do around it.

A Bad Air Brake Relay Valve

The job-related of the air brake relay valve is to remotely regulate the brakes at the rear of a semi-trailer in a tractor-trailer combination or a heavy truck. The friction used by this valve slows and also stops the brake drum’s turning, which inevitably stops the wheel.

However before, if the air brake relay valve is poor, it can cause many type of difficulties to the braking system. And among those troubles is leaking. First of all, a faulty air brake relay valve deserve to reason air to back-feed in the supply line, which causes air to leak.

How To Fix It

You will certainly need to detect which valve is back-feeding air. Afterward, you deserve to also deal with the leaking valves. But if the air brake relay valve is bad, you may have to replace it via a new one.

This deserve to be pretty difficult to find, and also that’s why you may need the services of a experienced mechanic to handle the problem amicably. But if you speak the leakage and air back-feeding, you have the right to still usage the valve.

Bad Tractor Protection Valve

A tractor protection valve is intended to protect the tractor air brake system if tright here is a trailer breakaway or a significant leak. Their major job-related is to prevent air loss from the towing auto.

Therefore, it shuts off air to the trailer prior to disconnecting the lines in an emergency. So, when the trailer supply line closes, the tractor defense valve on the towing truck additionally closes. On optimal of that, it prevents air loss out of the towing truck if tbelow is no trailer associated.

But choose all valves connected to the brake mechanism, the tractor defense valve can also cause problems if it’s faulty. It deserve to make air leak or back-feed. If you have such an concern, visit a mechanic to examine your ar.

Keep in mind that the tractor defense valve is regulated by the trailer air supply regulate valve. It permits you to either open or cshed the tractor security valve. Because of this, as soon as the trailer supply valve is opened up to permit air to the trailer, air push is additionally channeresulted in open the tractor protection valve and also permit air to the trailer company line.

On the contrary, if the valve closes, it ceases any air from getting out and enables air out of the trailer supply line that makes the trailer emergency brakes interact. Air deserve to additionally back-feed once the valve closes.

How To Fix It

If you don’t desire to have actually problems while applying emergency brakes, make certain you rearea a poor tractor defense valve. If air back-feeds or leaks from the emergency line, the breaks won’t engage as required.

Visit a skilled mechanic to deal with this difficulty as the tractor security valve have the right to be rather difficult to resolve. Also, you must check the supply manage valve and also encertain it’s additionally functioning fine.

Bad Spring Brake Valve

The spring brake valves were developed to perdevelop 3 main functions: to release the spring brake side of the brake chamber, fill the reservoirs, and interact the spring brakes for parking and also during emergency situations like a breakameans.

The spring brake operates in a basic means. The supply port on the valve is linked to an air line by a red coupler. So, when air is presented, it starts to fill the spring brake chambers using the shipment ports (emergency line and organization line).

Finally, the pressure creates till it cage the spring; hence, permitting the trailer to move. The reservoirs are likewise filled at the exact same minute.

When the press is dispatched, the valve dispatches the air from the spring side of the chambers. Hence, this locks the brakes. On the contrary, the air in the reservoir is trapped by a examine valve.


If this valve is poor, it will certainly cause the air to back-feed with the red port, which is the emergency supply line. Also, the spring brakes won’t work efficiently as soon as it concerns parking or throughout a breakaway.

How To Fix It

Start by inspecting the spring brake valve. If it’s not in great condition, gain a skilled mechanic to relocation it. A poor spring brake valve can cause a leak or air to back-feed depending upon where the damages occurred.

Wrongly Matched Trailer Lines

When connecting a trailer and tractor that’s towing it, you must make two vital connections for the brake device to function properly. The first link transports air to the trailer’s tank and also is described as an emergency or supply line. The various other link transports press for the company brakes and also is described as the organization line.

The emergency line have the right to easily be identified from the organization line with its colors. The emergency line is stood for by red lines and red couplers, while the service line is stood for by blue lines and also couplers.

Also, they differ in dimension, making wrong relations to be rare, also though some manufacturers offer the very same sizes.

Nonethemuch less, some world might still confusage these two lines and also plug them in the wrong places. If this happens, then the trailer brakes will certainly not occupational as necessary. Besides, it’s hazardous to drive a trailer with cross-connected trailer lines. Apart from that, wrong relationships will make air back-feed and leak.

How To Fix It

Unfavor other problems that we’ve highlighted above that require the attention of a expert mechanic, you don’t need one in this situation.

Sindicate change the trailer line to its port and also the business line also. Almethods be careful once connecting the trailer lines. What’s even more, the couplers have to additionally complement with the service lines.

Damaged Metal Trailer Couplers

Metal trailer couplers or gland also hands are important in the trailer braking system as they help affix the emergency and also business lines from the tractor or truck to the trailer.

The couplers are typically fitted through a rubber seal that avoids air from escaping. Furthermore, you must couple the best glad hand together to stop leading to problems.

Most steel trailer couplers are colored to avoid using the wrong coupler to connect the towing trailer and truck. Red is typically for the emergency line, while blue is for the business line. In some instances, tags are attached to the lines to determine the organization and emergency lines.

If you mix the metal trailer couplers, air will certainly be sent to the service line rather of filling the trailer tank. On the other hand, the press will certainly be sent to the trailer tank instead of the company brakes. This is extremely dangerous as there will be no air to release the trailer spring brakes.

But if the steel trailer couplers are damaged or dirty, they might proccasion the smooth circulation of air from the tractor to the trailer tank. As a result, this may make air back-feed also.

How To Fix It

Ensure to appropriately connect the metal trailer couplers and also lines. If the couplers are damaged and also leading to air to back-feed or leak it, relocation them.


All-in-all, air back-feeding in the trailer emergency supply lines is greatly bereason of bad valves. These valves generally attach the trailer’s brake system to the tractor’s brake mechanism.

Check and encertain that you’ve connected the emergency supply line and also organization line correctly.

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Even though many of these concerns deserve to be taken on by a DIY enthusiast, many trailer air brake device concerns must be tackled by a experienced mechanic.