What Is a Double Block and Bleed Valve?
A double block and bleed ball valve consists of two isolation ball valves and one bleed valve in a single valve assembly. It is efficient in weight and space. Because of this, it promotes less work during installation and maintenance. This allows the operator to find and control all three valves in a single location.
Its main function is to simultaneously isolate upstream and downstream lines while bleeding the body to maintain stable isolation. Because of its verified zero leakage, it is suitable for crucial services, such as toxic fluid operations and high-pressure systems.
Different Types of Block and Bleed Valves
A block and bleed system is made up of one or more block or isolation valves to prevent fluid flow. The valve types used in this manifold are the following:
Single Block and Bleed Valve
Also known as an isolation valve, a block & bleed valve is composed of a single block valve and bleed valve. The valve’s traditional layout promotes accurate flow regulation in a low-flow and non-hazardous environment. It is useful in applications where there are aggressive liquid and gaseous media that are not highly viscous.
Cartridge-type Standard Length Double Block and Bleed
This valve type consists of two block valves and one bleed valve in a single cartridge unit. This valve has the same configuration as a single-block ball valve. This will make it easier to connect into an existing pipeline without any pipeline reworking. The easy installation of these valves makes it suitable for applications that perform instrument draining and gauge isolation.
Three-piece Non-standard Length DBB
A three-piece non-standard length block & bleed valve is made of hub connections, flanges, and welded ends to fit the pipeline system. It has similar features with the single-unit DBB plus the benefit of bespoke face-to-face dimensions if necessary. This valve is designed for dangerous applications such as chemical seal isolation and chemical injection to prevent hazardous leaks.
Monoflange Double Block and Bleed Valve
A block and bleed monoflange is a combination of one or more isolation valves and one or more bleed valves. It provides isolation, venting, and instrument mounting in one unit. Monoflange valves are specially designed to provide compact installation for other valves and instruments. Their reduced weight and small leak paths help in the integrity of the system. They are ideal for petrochemicals, power stations, mining, and construction of general plants.
Custom Options & Design Features
Full and Reduced Bore
A full bore valve has a similar bore diameter, which is the hole in the ball, as the internal diameter of the pipe. It is used in media that contain mixed solids and liquids where flow restrictions could lead to separation of the substances. This could further lead to buildups that will reduce the desired flow in the pipes.
A reduced bore valve has a smaller bore diameter than the pipe it is on. It is lighter compared to a full bore valve and is ideal where weight and cost are important factors. A reduced bore is also suitable in services where the pressure drop through the ball valves does not have a significant effect during operations.
An anti-blow out stem contributes to the stability and service life of the valve. It means the stem is isolated from the valve body to prevent the risks of a blowout. The stem is held by the stem housing, which is secured by the body. When there is high pressure on the valve, the stem will be kept in place by the stem housing preventing it from flying off.
The anti-static on ball valves is an added fireproof safety to the double block and bleed ball valves. When the valve operates, the friction between the metal ball and soft seat will cause friction and static charge inside the body. This increases the risk of spark and ignition of flammable liquid. The anti-static device produces a ground path and maintains electrical continuity between the valve body, stem, and ball.
A. Internal Leak Prevention
SIO is equipped with a fire-safe design that will help minimize internal leaks in case of accidental fire. When sealing materials are damaged during a fire, the metal seat retainers will connect with the ball to stop fluid flow to control internal leakage, so as to prevent fire. The secondary graphite seal will further help prevent leaks during and after the fire.
B. External Leak Prevention
SIO’s double sealing feature will prevent external leaks from the valve stem area. The O-rings and graphite seal will act as protection against leakage throughout the valve body. Even after an accidental fire has burned down, the o-rings and graphite seal will stay intact to prevent external leakage.
Spring-loaded seats will increase the stability and efficiency of the valve. Fluids with high velocity and pressure coming from the upstream direction could damage unsupported seats. With spring-loaded seats, there is continued tightness during quick temperature changes. They also permit the valve to seal in two directions, which makes valve installation possible in any flow direction.
Emergency Sealant Injection System
An emergency sealant is an essential feature that prevents leakage from progressing. Paired with a check valve, the emergency sealant will provide backup sealing in case of accidental fire. When the sealing materials are damaged and there is leakage, the emergency sealant will be inserted into the injection fittings. SIO’s emergency sealant injection system will provide a reliable and temporary seal even when there is severe leaking in the valve.
Double Block and Bleed Valves VS. Double Isolation and Bleed (DIB) Valves
Double block and bleed valves(also known as DBB) and double isolation and bleed valves (also known as DIB) have quite similar functions and are used in similar applications. Both can create isolation in upstream and downstream lines. Both of them are ideal for high-temperature and high-pressure applications, here are the 2 main differences:
Difference by Blocking Pressure
The main difference between the two is that a DBB valve can block pressure both from upstream and downstream lines. When there is leakage on the first seal, the second will not seal in the same direction.
Meanwhile, a double isolation and bleed valve has two separate seals to block pressure from one side only. Using a DIB valve will mean double security. It is better for applications that require an additional barrier for safety purposes.
Difference by Relieving Pressure
Another significant difference between the two is their capacity to relieve pressure. A DBB valve usually has two unidirectional self-relieving seats that don’t depend on an outside system for pressure relief.
A DIB valve uses one to two bidirectional seats so it can provide double isolation against pressure at the valve’s both sides. The downside to this is that the valve is not self-relieving and can only relieve pressure within the seats.
How Does a Double Block and Bleed Ball Valve Work?
A double block and bleed valve has three valves in one – two isolation valves, usually ball valves, and one drain valve, usually a ball or needle valve. The valves are installed as a manifold or unit to provide positive isolation.
The double block bleed valve is used to prevent fluid flow from getting into an area where there is continued work. This is to keep the fluid or steam in the upstream line from reaching the components in the downstream line of the system. Both of the isolation valves will close completely to secure the bleed flange or cavity. The drain valve will then open to drain the fluid or steam. This will ensure safe working on the depressurized area of the system.
For example, an integral double block and bleed valve is used to stop the fluid flow from passing through certain equipment. The fluid from the equipment’s side of the DBB manifold is drained through the vent or drain valve. This will make the service, such as replacement, repair, or maintenance, safe for the equipment.
The block & bleed valve is ideal for critical process services, including high-pressure and high-temperature systems and steam pipelines. Due to its reliable tight sealing, the double block and bleed system ensures proper isolation before equipment maintenance, replacement, or repair.
Applications for Double Block and Bleed Ball Valves
Oil and Gas Industry
The process and transmission of oil and gas require absolutely no leakage during the entire operation as this could be hazardous. Double block and bleed ball valves are known to be consistent in preventing any leak. That’s why they are widely used in the oil and gas industry.
A DBB valve is helpful in petrochemical applications to control hazardous chemicals and toxic waste. Chemical stamping and injection require a guarantee that there will be no potential leaks. The valve’s interlocking feature will prevent any leakage or mixing of liquid with critical elements.
Water services near municipalities and waterways require crucial isolation to prevent leaks. The functions of SIO’s double block and bleed ball valve will provide a tight seal to both upstream and downstream lines without being affected by pressure and vibrations. Once leaks are identified, the block valves will close to isolate the spill and prevent further damage. This is best for providing protection against natural disasters and third-party damages.