FreightViking is reader-supported. We may earn commissions if you buy through our links. Also, as an Amazon Associate we earn from qualifying purchases.

What Is A Dump Valve On A Semi Truck? (Explained & Solved!)

Have you ever heard people talking about dump valves?

If you’ve been trying to understand what a dump valve is and why they are essential, you’re in the right place.

We are specifically going to be talking about dump valves found on semi trucks.

Read on to find out more…

Here is a short summary to What is a Dump Valve on a Semi Truck:

Semi trucks have dump valves that allow them to lower and raise the suspension by cutting off the air supply and releasing the air in ‘air bags’ that are found on top of the axles. This can be helpful in several scenarios such as tight corners and loading or unloading cargo.

What are Air Dump Valves on a Semi Truck?

Air dump valves are an essential part of the suspension on a semi truck. Dump valves allow the air to be released from the suspension’s air bags.

They are often controlled by the driver in several different scenarios. They have an important purpose and need to be used properly.

In some cases, the air will be released from the air suspension to allow the semi truck to make tighter turns. Releasing the air will making tighter turns less stressful on the axles of the semi truck.

If the semi truck takes tight turns without releasing the dump valves there is a risk of flat spotting the tires and causing excessive wear. In addition, it also puts strain on the suspension.

Semi trucks will also dump air from the suspension to make the process of loading and unloading cargo easier. Dumping air from the suspension will lower the semi truck, making it easier to load cargo.

Do Semi Trucks and Semi Trailers Have Air Dump Valves?

Both semi truck and trailers have dump valves. This is especially necessary when the trailers are extremely long and would struggle with tight turns.

Some trailers that are more flexible than others also run the risk of flipping over if the dump valves aren’t used.

During a tight turn, a trailer can become bound up and twist, similar to a metal ruler if you were to push one side while holding the other side. At some point, the trailer will unload and roll over.

Just like with the semi truck tractors, if the dump valves are not used on the trailer it can send a lot of stress through the suspension and the tires.

How do Dump Valves in a Semi Truck Work?

Most semi trucks and semi truck trailers work on air suspension. This helps the semi truck in several ways, such as ride height and smoothness over rough roads.

Each axle has ‘air bags’ that are used to power the springs in the suspension, giving the semi truck its height and smooth ride.

Air dump valves will exhaust the air in these airbags. When a driver flips the dump valve switch, a piston pushes the air out of these air bags.

This lowers the ride height significantly and will weaken the tension on the springs in the suspension.

When should you Use Your Dump Valves in your Semi Truck?

There are several different scenarios for when drivers need to use the dump valves on their semi trucks.

The main one is to load and unload cargo from the semi truck. Releasing the air from the suspension will lower the semi truck and the trailer, making it much easier to access it.

The dump valves are also exhausted to help semi trucks to back up into a trailer to get it hooked on or off. Lowering the semi truck allows it to move into position much easier.

When making tight turns and maneuvers, semi trucks also need to release their dump valves to allow the truck to turn tighter.

If a semi truck makes a tight turn without releasing the dump valves, it can also cause excessive damage to some tires, such as flat spots and irregular wear patterns.

How Many Dump Valves do Semi Trucks Have?

In most cases, it entirely depends on the semi truck. Most modern semi trucks will be equipped with air dump valves for the tractor and for the trailer.

However, some semi trucks do not have dump valves at all. They can be installed afterward, though, if you believe that you need them.

Some semi trucks will have dump valves just for the tractor, and others will have dump valves for the semi truck tractor and the trailer.

Where are Dump Valves Located in a Semi Truck?

Semi truck dump valves are found on the rear suspension of the truck. There are lines that connect the dump valves to the air bags on the suspension.

All of this is also connected to the cabin, where the driver can operate the dump valves by using a switch on the dashboard of the semi truck.

How do You Switch Open an Air Dump Valve in a Semi Truck?

The dump valves on a semi truck are operated by a switch in the cabin. The switch can often be found on the dashboard of the semi truck.

When you switch the dump valve controls, the dump valve shuts off the air supply line and lets the air bag line vent to the outside.

Are Dump Valves Good for a Semi Truck?

Dump valves are essential for semi trucks. In most cases, they can help the semi truck to coordinate tight corners easier.

It will help to take the stress off the axles, tires, and suspension. It also makes it much easier t load and unloads the trailer by lowering the height of the suspension.

If the dump valves are not used while making tight maneuvers, you can destroy the tires or put a lot of strain on the suspension, which could eventually break.

Can you Drive at High Speeds with Dump Valves Open?

You should never drive at highway speeds when the dump valves are open. In fact, it is best to keep the speed under 15 miles per hour when the dump valves are open.

When the dump valves are open, it means that the weight shifts onto another axle. For example, if the rear axle’s dump valves are open, all the weight will be on the front axle.

This can be an extreme amount of stress on one axle, which can be aggravated when going over bumps at high speed.

When the dump valves are open, it means that the suspension will not be cushioned in that area, which means it will be more vulnerable.

Do Air Dump Valves Affect your Axle and Tires?

Air dump valves are beneficial to your axles and tires. This is especially important when the semi truck is making tighter turns.

If the dump valves are not opened when turning, the tires can scrub on the road’s surface, which will cause flat spots and extreme wear patterns.

This will cause the tires to become damaged, which will shorten their lifespan. Over the long term, it will end up costing you more money.

In the same scenario, stress can also be put on the axles and the suspension. Over time the suspension could degrade and fail entirely.

The dump valves will also help with flexible trailers that can become bound up and flip over when the stress unloads.

Do All Semi Trucks have Dump Valves?

Not all semi trucks have dump valves installed. The majority of modern semi trucks do have dump valves, though.

Some semi trucks only have dump valves for the tractor. However, others have dump valve switches for the tractor and the trailers.

Dump valves can easily be installed in a semi truck if they are not equipped with dump valves.

It is recommended to use a mechanic to assist with the job because it requires some mechanical knowledge.

How to know if your Semi Truck has a Bad Dump Valve?

You can generally tell if the dump valve on your semi truck is bad if it is either stuck open or stuck closed. In other words, when you flip the dump valve switch, nothing happens.

A dump valve can also be bad if you notice the suspension movement becoming slower than usual when you switch the dump valves. This could be a sign of a leaky suspension.

If the semi trucks ride is suddenly hard and uncomfortable, it can also indicate a lousy dump valve or a bad suspension.

In some cases, you might even see the semi truck lean toward one side or another. This can indicate that the dump valve on a specific side might be faulty.

How to Maintain a Dump Valve on a Semi Truck?

In most cases, it is best to take the semi truck to a professional to have the dump valves maintained. It can be an intricate process.

To properly maintain or repair a dump valve, it needs to be removed from the suspension and inspected for dirt and damage.

It may need to be taken apart, cleaned, and have some parts replaced. The airlines might also need to be cleared or repaired in some cases.