How Does a Double Block and Bleed Valve Work  

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Double block and bleed valves are essential components in many industrial applications because they are specialized valves designed to shut off the flow of fluids at two points while still allowing personnel to access the system and make adjustments. They offer greater control over regulating media flow and provide a reliable way to ensure that piping systems remain safe and secure when they can’t be actively monitored.

Dombors double block and bleed ball valve
Source: Dombor

Understanding how these valves work and their features are key to getting the most out of them. In this article, consumers will take a closer look at the process behind the double block and bleed valves so consumers can better understand their importance as part of their operations.

What is Double Block and Bleed Valve?

A double block and bleed valve or DBB ball valve is a type of separation valve used to perform two functions at once. It blocks the flow of fluid through it, meaning that no material can get further downstream, and forces any pressure already in the system out through a bleed mechanism connected to the valve – hence its name.

Most of the industrial valve supplier typically consists of two shutoff valves (either ball or gate), a needle valve, and an access connection to relieve the pressure in between both shutoffs. 

It is designed to ensure there is no medium trapped between the two so that when one valve is open, the other remains closed, thus preventing cross-contamination or unintended emission.

This type of valve is often used in systems with hazardous materials and/or high-pressure applications.

How Does the Double Block and Bleed Ball Valve Works?

The basic design of a double block and bleed ball valve consists of two tightly sealed blocking systems that are separated by a third “bleed” port. The first two ports are referred to as block valves, which halt the flow of liquid or gas through the valve.

The bleed port is then used to release any remaining pressure or air from the system before its final closure. The primary benefit of this setup is the ability to hold back pressure while still allowing for partial or complete shut-off of the system.

In operation, a DBB works by turning the handle on top of the valve to its open position. This opens both block valves, allowing fluid or gas to pass through the valve. When it’s time to shut off the flow, you turn the handle again to close both block valves and open the bleed port. This releases any leftover pressure inside the valve, enabling it to completely shut off the flow of fluids or gasses.

The valve also has a vent or bleed port located between the two seals. When the valve is turned on the closed position and there is fluid or gas trapped between the seals, the vent port can be opened to release the pressure and allow the trapped fluid or gas to escape.

How is the Double Block and Bleed Valve Constructed?

To construct a double block and bleed (DBB) valve, an industrial valve company should choose first a suitable piping system using high-density polyethylene (HDPE) pipe. Two block valves should then be installed at both terminal ends of the HDPE pipe for isolating both ends of the pipe from each other. An isolation valve should also be placed between these two block valves to allow for safe pressure regulation.

Dombors Double block and Bleed valve
Source: Dombor

A bleed valve should further be inserted between the two block valves and this will enable the release or evacuation of air or other gasses before the pressure test of the HDPE piping system. In addition, a pressure regulator should be installed between the two block valves in order to achieve an appropriate amount of pressure.

Lastly, it is crucial to ensure that the valves used in the HDPE pipe system are of high quality and sourced from a reputable valve manufacturer. Valves play a critical role in controlling the flow of fluids, and any failure in their performance can lead to significant safety and environmental risks.

Proper selection and installation of valves can prevent potential hazards and ensure the optimal performance of the HDPE pipe system. It is recommended to consult with the valve manufacturer or a qualified engineer to determine the appropriate type and size of valves needed for the specific application and to ensure that they are installed and tested according to industry standards.

Contact Double Block and Bleed Valve Manufacturer – Dombor

Dombor is a leading valve manufacturer of double block and bleed valves. Located in China, Dombor has been manufacturing high-quality valves for different industries since 2001. They specialize in providing reliable double block and bleed valves that are suitable for extreme pressure applications. All their products are designed to meet stringent international standards such as API 6A, BS 5158, and ISO 9001:2015.

As an industrial valve supplier, they offer an array of ball valves in various sizes and pressures. Their double block & bleed valve offers superior reliability with ultra-tight shut-off performance. It is designed with an innovative combined modular construction which reduces the weight of the valve while maintaining high-pressure containment capability.

Dombors showroom with the different types of valves the offer
Source: Dombor

It also features an integrated seat design which prevents cross-contamination, making it ideal for dealing with hazardous fluids. With its superior resistance to corrosion and wear, it can be used safely and reliably in extreme temperatures and critical processes.

To ensure the highest quality of their products, they have developed advanced testing facilities to test every component and material used in the manufacturing process. The rigorous testing ensures that no component causes any harm to the environment or affects its efficiency or performance.


Double block and bleed valves are highly reliable isolation valves used in many applications to shut off the flow of fluids at two points while still allowing access to the system for maintenance. When selecting the right one for your system, it is crucial to understand how they work and the features they offer.

By doing this, consumers will be able to make an informed decision that best fits the purpose of their operation. Dombor is an industrial ball valve manufacturer that specializes in providing reliable double block and bleed valves designed. With their exceptional quality control and rigorous testing procedures, customers can rest assured that their valves are always up-to-standard.