How Does a Vacuum Breaker Work? (Walkthrough & Benefits)

Like most homeowners, you probably don’t know how a vacuum breaker works. Here’s a quick breakdown of what it does and how it does it.

The Vacuum Breaker works like a normal check valve. Through the air inlet, air from the outside can get into the system. But the vacuum breaker shuts down tightly when water or steam tries to get out.

I’ll go into more detail below.

How Do You Use a Vacuum Breaker?

The right way to use a vacuum breaker in a steam system and why you need one are shown in the following example.

vacuum breaker in steam piping system

Think about how this is piped:

We have steam from the boiler at 10 psi or a little more. Then there is a control valve, which goes through a pipe to the top of a heat exchanger.

We have a line for condensation that leads to a steam trap. The water goes through a check valve into our atmospheric condensate return system.

So, if the control valve is fully open, there is a slight difference in pressure between the valve and the heat exchanger. But we’ll see that there’s still enough differential pressure down here to push the condensate through the primary trap, and everything works fine.

As the product inside the heat exchange starts to warm up, our control valve will modulate down, so you can see that the pressure starts to drop.

Also, there will be less pressure at the condensate line. If the condensate pressure needs to be higher to force the condensate through the steam trap, or if there is more modulation in the control valve, which can cause backflow to the heat exchanger or, even worse, create vacuum pressure, there will be problems.

This can cause problems with temperature control down the line, water hammer, the chance of freezing, or corrosion of our system over time, so the issue needs to be fixed with a vacuum breaker.

Suppose we put a vacuum breaker before the heat exchanger and open this valve. In that case, you’ll hear air from the outside coming into the vacuum breaker, and you can watch the gauge go from vacuum pressure to zero, meaning that there is no pressure in the system.

We can always stay below zero, even if we have positive pressure, or go down to zero. Now, if we put our trap 14 to 18 inches below our heat exchanger, we can always ensure that we have positive pressure. If a vacuum breaker is put in the right way, we will have good drainage.

What Does a Vacuum Breaker Do?

So, to sum up, the pros, here are the top 4 reasons why your system should have a vacuum breaker:

  1. It helps ensure that all the condensate drains out in both on/off and modulating applications.
  2. It keeps you safe from a water hammer.
  3. It makes the temperature more stable and less likely to change.
  4. It helps keep products from going to waste.

How Does Vacuum Breaker Work?

Usually, a vacuum breaker has a plastic disc that is pushed forward by the pressure of the water supply and covers small vent holes. If the supply pressure drops, the disc springs back, opening the holes that let air in and stopping water from flowing backward.

pressure vacuum breaker illustration

The vented chamber opens when the air pressure exceeds the water pressure. This breaks the suction caused by the low pressure and stops water from flowing backward. Before the water gets to the sprinkler valves, a pressure vacuum breaker is put close to the water source.

You have to put it above the highest point in the system, usually, the sprinkler head that is the highest or the highest slope in the yard.

Why Do You Need a Vacuum Breaker?

Contamination of the water supply can have many different effects, so preventing it is essential. Most local building codes say that all water systems need a device to stop water from flowing backward.

Since most homes only have one water system for drinking water and all other uses, including irrigation, there is always a chance of contamination through cross-connections.

Backflow can happen if the water pressure in the home’s main water supply suddenly drops. For example, if the city water supply is cut off for any reason, this could cause the home’s main supply to have low pressure.

When there is negative pressure, water can flow backward through the pipes. This is called siphoning. Even though this doesn’t happen very often, it could cause water to be sucked out of sprinkler lines and into the main water supply. From there, it could get into your home’s plumbing.

What are The Types of Vacuum Breakers and Their Work?

There are many different kinds of vacuum breakers. The atmospheric and pressure vacuum breakers are the most common.

Atmospheric Vacuum Breakers

An Atmospheric Vacuum Breaker (AVB) is a backflow prevention device that uses a vent and a check valve to keep non-potable liquids from being sucked back into the potable water supply. This is called back-siphonage, caused by negative pressure in the supply pipes.

Pressure Vacuum Breakers

A pressure vacuum breaker (PVB) is an essential part of irrigation systems. It keeps water from flowing backward from your irrigation system into your home’s freshwater supply, which is your drinking water.

A pressure vacuum breaker comprises a check device or check valve and an air inlet that lets air out into the atmosphere (open-air). Usually, the check valve is made to let water through but keep the air inlet closed.


Why is a Vacuum Breaker Important?

A vacuum breaker is important because it keeps water from going backward. Backflow can make your irrigation and plumbing system less effective by letting water and waste flow back instead of forwards. This can cause harmful bacteria to get into your pipes and fixtures. So, a vacuum breaker is an important part of making sure that contamination doesn’t happen.

How Does a Vacuum Breaker Prevent Backflow?

A vacuum breaker stops backflow by forcing air into the system, which makes a pressure difference. Most likely, the water will move toward the air being pushed in. If the water flowed the other way, there would be no difference in pressure, so the air being pushed into the pipes would push its way past the water molecules.

What’s a Code Requirement for Vacuum Breakers?

A vacuum breaker is needed at any place where water is used for something other than drinking. State and federal laws say that vacuum breakers must be put in outside faucets, commercial dishwashing machines, mop sink faucets, and dish sink sprayer hose faucets.

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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