What Does A Vacuum Brake Booster Check Valve Do?

What does a vacuum brake booster check valve do? A vacuum brake booster helps to increase pressure in your car’s braking system. But why would you need that, and how does it work? Let’s find out in the article below.

The braking system is essential for your car. So, you need to make sure that it is always functioning well.But have you ever wondered how your 4000-pound vehicle stops so quickly just by applying force on your brake pedal? 

Thankfully, most cars today are equipped with brake boosters that provide extra power to your car’s braking system.

The brake booster is a device that increases the force applied on your brake pedal to the master cylinder and thus helps stop the vehicle more quickly and comfortably. The check valve is one of the vital components of the braking system of your car.


What Does A Vacuum Brake Booster Check Valve Do


So what does a vacuum brake booster check valve do? The check valve sucks all the air of the brake booster and does not allow entering the master cylinder and brake lines. Remember, the air inside the brake lines can adversely impact your braking system. It can make the pedal spongy. As a result, you will find it difficult to stop your vehicle, which is dangerous while driving on the road.

The check valve is usually neglected by most car divers. But it can get wear and tear with time, or sometimes it can fail permanently. So I will advise you to check or clean the check valve of the brake booster from time to time.

The article discusses check valves in the brake booster in detail. So, you can keep on reading the article for more information.


You might also like to read: What Does A Brake Vacuum Pump Do?


What Does Vacuum Brake Booster Do?

The brake booster of your car is usually located on the firewall inside the engine compartment. The booster has a simple construction.I am listing some of the main components of the brake booster

#1. Shaft

You will find two types of the shaft in the brake booster, i.e., primary and secondary shaft. The primary shaft links the brake pedal and diaphragm. The main purpose of this shaft is to open and close the valve for the entry and exit of atmospheric air. 

The output shaft links the diaphragm and master cylinder. The primary purpose of this shaft is to transmit the force from the diaphragm to the master cylinder.


What Does A Vacuum Brake Booster Check Valve Do

#2. Diaphragm

A diaphragm divides the brake booster into two halves, i.e., the front chamber and the rear chamber. You will find a thick hose that connects the front chamber of the brake booster to the intake manifold as a vacuum source.

#3. Valves

You will find two valves in the brake booster: a vacuum valve and an atmospheric valve. 

The vacuum valve is a one-way valve and maintains the vacuum inside the brake booster. It allows the air to exit but doesn’t let any air to enter inside the brake booster. 

The atmospheric valve allows the air to enter and leave the brake booster.


You might also like to read: My Car Dies When Brakes Are Applied, What Should I Do?


How Does a Vacuum Brake Booster Work?

Whenever you don’t push the brake pedal, both the front and rear sides of the chamber are supplied with a vacuum. But when you press the brake pedal, the shaft will move forward and open the valve at the rear chamber. 

It allows the atmospheric air to enter the chamber, but the other half of the chamber is still under vacuum. The pressure difference created between the chambers helps push the shaft forward and pushes the push rod of the master cylinder.

When you leave the pedal, the spring makes the shaft return to its original position, and the vacuum is equalized on both diaphragm chambers.

Where Does The Brake Booster Vacuum Line Go?

To find the brake vacuum booster you need to look at the firewall on the side where the driver sits. Your master cylinder will be in line with it.


What Does A Vacuum Brake Booster Check Valve Do

What Are The Functions Of Check Valve?

The check valve has mainly three functions which I am listing below.

#1. Helps In Maintaining Vacuum Inside The Booster

The check valve helps in maintaining the vacuum inside the brake booster. It does not allow the external air to enter the vacuum booster when the engine is not in working condition.

#2. It Helps In Releasing Build Up Pressure

Pressure builds up inside the vacuum brake booster when you depress your brake pedal. But after you release the pedal, the pressure needs to be released. Thanks to the check valve. It helps remove all the air out of the vacuum brake booster through the hose.

#3. Prevents Air To Enter Braking System Of Your Vehicle

The function of the check valve is to restrict the air to enter the master cylinder and brake lines. If the air bubble is present in brake lines, then it adversely affects your car’s braking system.


You might also like to read: 6 Reasons Your Car’s RPM Goes Up When Pressing Brake


What Are The Signs Of A Damaged Check Valve?

#1. Your  Brake Pedal Become Hard

If the valve is worn out, the vacuum is reduced in the power brake unit. Consequently, you require to depress your brake pedal quite hard to engage.


Changes in the brake pedal are dangerous. Take your car to the nearest automobile repair shop. He will inspect the vehicle and replace the check valve with a new one.


What Does A Vacuum Brake Booster Check Valve Do

#2. Spongy Brake Pedal

Sometimes the check valve hets blocked because of dust or debris and hence unable to carry out its function. The brake booster will have air molecules that cannot be removed by the check valve. 

Consequently, the air enters the brake lines and master cylinder and decreases the pressure of the hydraulic fluid. So, your brake pedal goes down to the floor while driving, which is dangerous.


Take your vehicle to the nearest mechanic. He will not only install a new check valve but also bleed your fluid for removing all the trapped air molecules.

#3.Your Brake Will Stop Working

When the check valve of the vacuum brake booster is damaged or broken, then there is a possibility that your brake will stop working.


Stop your car in a safe place and tow your car to the nearest mechanic. He will inspect your vehicle and may install a new check valve.


You might also like to read: 7 Reasons Why The Brake Pedal Goes To Floor When Engine Starts


How Will I Know The Check Valve Of My Brake Booster Has Gone Bad?

  • Park your car
  • Open the hood and locate the vacuum booster
  • Remove vacuum pipe and check valve
  • Start blowing air inside the pipe by an aspiration bulb.
  • If the air comes into the vacuum pipe, it will confirm that the air is leaking from the check valve.


What Does A Vacuum Brake Booster Check Valve Do

Frequently Asked Questions

#1. How can I find out that the check valve is faulty?

  • You will find difficulty in pressing the brake pedal
  • The brake pedal gets spongy and touches the floor while driving
  • Your brakes may fail completely.

#2. What is the purpose of a check valve in a vacuum booster?

The purpose of the check valve is to expel all the air molecules that are trapped inside the vacuum booster. Moreover, it helps maintain a vacuum inside the brake booster and prevents air molecules from entering the brake lines and master cylinder.

#3. What are the consequences if a power brake booster has a vacuum leak?

When a power brake booster has a vacuum leak, there will be unregular airflow in the induction system of your vehicle. Again there will be a sudden drop in the engine’s rpm, and possibly the engine may cease to work.

#4. Do all brake boosters have a check valve?

Yes, all brake boosters have a check valve. The primary function of the check valve is to maintain a vacuum inside the brake booster even if the engine s turned off.


You might also like to read: Spongy Brake Pedal When Engine Running – What to Do?


A Few Final Words

A vacuum brake booster increases the efficiency of the braking system. The check valve is an essential component of the brake booster. 

A faulty check valve will cause problems at the time of applying brakes. It may make the brake pedals hard and increase your car’s stopping distance, which is quite dangerous.

So, if you find your check valve faulty, then better replace it with a new check valve as soon as possible. 

Thank you for reading the article, we hope that we were able to answer all your queries. If not, please write to us in the comment below and we will help you as soon as we can.

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Sean Mendez

Hi, I am Sean, a self-confessed petrolhead. I live in Boise, Idaho with a busy family of four and our energetic Labrador retriever. Thank you for visiting my website. You can find my email on the contact page.

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