How Does a Double Block and Bleed Ball Valve Work? - SIO

How Does a Double Block and Bleed Ball Valve Work?

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Double block and bleed valves are used for isolation in critical applications. They also prevent product contamination and maintain system integrity. DBB valves make it easy to remove machinery for cleaning, repair, and maintenance. 

Before DBB valves were used, isolating pipelines and machinery was a difficult process. You had to install two individual isolation valves, a spool piece, and a bleed valve to maintain system integrity. The machines were expensive and heavy. There was an increased risk of emission since multiple machines had to be installed. It was also difficult to operate the system since the technician had to check three valves at the same time.

valves and appliances for gas pumping station

DBB valves solved all these problems. They are a single valve unit so they have a smaller installation footprint. They save on extra piping requirements and reduce weight in critical areas. They are easy to operate since the technician only needs to check a single unit. DBB valves are now used in critical applications across different industries. 

How is a Double Block and Bleed Valve Constructed?

A double block and bleed valve features two block valves and a bleed valve. The block valves isolate the upstream while the bleed valve drains excess medium. DBB valves are very flexible when it comes to design. They can be custom engineered to adjust various lengths, heights, and connection sizes. You can also add certain features. For example, a sealant injection can fortify the valve’s tight-sealing abilities.  

DBB valves are available in modular, monoflange, and root configurations. Below is an image of a modular double block and bleed valve. It features two block valves installed side by side with a bleed valve installed in the middle. Modular DBB valves are commonly used for toxic fluid operations in high-pressure systems. 

Plane figure of double bleed valve block special valve

Source: http://www.piping-engineering.coml

Monoflange valves usually feature one block valve and one bleed valve. But they can house more than one of either as well. If you look at the diagram below, you can see that the monoflange valve is compact in size. Monoflange valves are used in petrochemical factories, power stations, and mining and construction.  

Plane figure of monoflange bleed valve


DBB valves are also available in a variety of conventional configurations. You can see the details of some of these models in the diagram below. The configuration you choose will depend on your application, media, and environmental factors. 

Plane figure of conventional double bleed valve


Difference Between DBB and DIB Valves

Double block and bleed valve (DBB) and double isolation and bleed valve (DIB) perform similar functions. Both valves provide simultaneous upstream and downstream isolation in high-pressure, high-temperature situations. But these valves are not the same.

DBB and DIB valves may look the same from the outside, but their construction is different. DBB valves are designed to provide a seal against pressure from both sides of the valve. DIB valves go one step ahead and provide an additional seal against pressure from only one side. DIB valves are used in operations where there is low tolerance for leakage. They are also used to maintain the cleanliness of the medium. 

Another difference between DIB and DBB valves is the way they release pressure. DBB valves feature two unidirectional seats that relieve pressure on their own. DIB valves have two bi-directional seats that cannot relieve pressure on their own. You have to install a separate pressure-relief mechanism when using DIB valves. 

How Do Double Block and Bleed Ball Valves Work?

Double block and bleed ball valves feature three ball valves. The valves are attached as either a unit or a manifold inside one compact body. The two-block valves are installed on either end of the DBB valve while the bleed valve is in the middle. The DBB valve functions by isolating the onstream flow of fluid or gas from either end of a pipeline. It then uses the bleed valve to drain the excess medium.

simple plane figure of double block and bleed ball valve

For example, if you want to repair machinery that is part of a critical process unit, you have to isolate it from the rest of the system. To do this, you have to install a DBB ball valve between the pipeline and the machinery. This DBB ball valve will feature two ball block valves and one ball bleed valve. One block valve will isolate the upstream of the medium while the other will shut-off the downstream. When both block valves are tightly sealed the flow of medium to and from the machinery will stop. You can then open the side of the DBB valve that is connected to the machinery to drain any residual medium. Once it is drained, you can seal the bleed valve shut. 

You can then repair, replace, or maintain the machinery without disturbing the unit. In high-pressure, high-temperature applications, DBB ball valves can be used to cordon off the area that needs repairs. This is done by depressurizing the specific area that requires isolation. DBB valves’ reliable tight sealing ensures complete and reliable isolation of critical applications.  

Kinds of Valves Used in Double Block and Bleed Ball Valves

Floating ball valves and trunnion mounted ball valves can be used to construct a double block and bleed ball valve. But generally, trunnion mounted DBB ball valves are preferred. Trunnion mounted ball valves can handle high-pressure operations and provide better bi-directional shut-off. These DBB valves feature two trunnion ball valves as block valves. Another trunnion mounted ball valve or a needle valve can be used as the bleed valve. 

Double Block and Bleed Ball Valve

You can use many variations of valves to create a DBB valve that gets the job done. Gate and globe valves can be used as block valves while ball valves are used as bleed valves in different applications. Expanding plug and expanding gate valves can also be used to block the flow while a needle valve bleeds the surplus medium. The type of DBB valve you use depends on the nature of the fluid, its pressure and temperature, and many other factors.

How to Choose the Right Double Block and Bleed Valve?

There are many factors that determine which DBB valve is best for your needs. Let’s take a look at some of these factors and how you can use them to choose the right DBB valve:

Nature of Application 

The nature of your application will define the kind of DBB valve you need. For example, if you need to maintain system integrity while you repair a certain part of the pipeline, you can use a DBB valve to get the job done. Two gate valves can block the onstream. A ball valve can bleed any fluid from the isolated area of the pipeline before it is repaired. 

Type of  Media 

The type of DBB valve you choose depends on the kind of media you are trying to regulate. Viscous liquids and thick gasses will require full bore ball, globe, or gate valves as block valves. While a needle valve can be used as a bleed valve. Corrosive media may require stainless steel DBB valves or carbon steel ball valves that have been fortified to block the media without sustaining any damage. 

Pressure and Temperature 

The pressure and temperature requirements of your operation will determine the kind of DBB valve you need. High-pressure, high-temperature operations will require anti-static ball valves as block valves. These metal seat ball valve are not affected by pressure changes or vibrations so they are safe to use in critical operations. In low-pressure operations, you can use a single DBB gate valve with flexible wedges and a body bleed valve.

When are Double Block and Bleed Ball Valves Used?

DBB ball valves are used for many different applications across different industries. They help check the integrity of seat seals in different valves and machinery. DBB ball valves are used in industries like LNG, petrochemical, chemical, water and gas, and more. They are also used in transmission and storage, refined products transmission lines, natural gas industrial processes, and mainline and manifold valves in liquid pipelines. 

Double Block and Bleed Ball Valve

DBB valves are the key to isolating critical operations where the liquid flowing upstream and downstream must not leak or be mixed with each other. For example, in liquid service near waterways or municipalities, DBB valves like the SIO DBB Ball Valve can provide a tight mechanical seal both upstream and downstream at the same time. The trunnion mounted ball valves inside the DBB valve have anti-blowout stems. They are also anti-static and feature spring-loaded seats. This means they can easily handle the pressure variations and vibrations. 

DBB ball valves are also used in the meter calibration market to ensure correct calibration in every operation. The valves in a meter system must seal tightly. Even a small leak will cause errors in the meter calibration that will persist throughout the operation. This will make the end-users lose a lot of time and money. Choosing the right API-6D DBB ball valve can help get the correct calibration almost every time.

What are the Benefits of Using Double Block and Bleed Valves?

Double block and bleed valves prevent leakages and maintain system integrity. They are used for critical isolation in high-pressure, high-temperature operations.

Here are some other benefits of using DBB valves:

Less System Vibration: DBB valves are anti-static and feature anti-blowout stems making them resistant to system vibrations. They are unaffected by changes in pressure and thus do not cause changes in pressure of liquid or gas flow.

Compact Design: DBB valves have a single body that is compact and light in weight. They are easy to install and prevent leakages as there are less flanged faces. Their compact configuration makes them convenient to operate as well.

No Need For Supporting Brackets: DBB valves are a single unit that can be installed by using bolts. This means you don’t need supporting brackets. Installing DBB ball valves is efficient and simple.

Increased Plant Safety: DBB valves provide a tight drip seal ensuring zero leakages. This improves plant safety in critical applications where leakages can lead to contamination.

Improved System Reliability: DBB valves are great for isolating key areas in any unit. They block valves provide a tight seal while the bleed valve drains any remaining medium. Bleed valves also ensure the block valves are sealed tightly, ensuring system reliability.


Double block and bleed ball valves maintain system integrity by isolating critical areas in the unit. You can then repair, replace, or check these areas without disturbing the system. These valves are used in many industries including oil and gas, water, petrochemical, and more. SIO as one of the best high pressure ball valves manufacturers, valves are available in different configurations and are customizable, like carbon steel ball valve or ball valve flange type. Choosing the right DBB valve depends on how you want to use it and where. If you’re not sure which DBB valve is best for your project, get in touch with us. 

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