API 6D defines a double block and bleed valve as a "single valve with two seating surfaces that, in the closed position, provides a seal against pressure from both ends of the valve with a means of vending/bleeding the cavity between the seating surfaces."

There are a couple different styles of double block and bleed valve. One style has two independently seating valves inside, with a bleed or drain valve. This configuration is referred to as a double isolation and bleed (DIB). The DIB valve can isolate either side of the valve (bi-directionally) to vent or bleed the cavity and isolate piping.

This trunnion ball valve provides double block and bleed in a single valve. This style can isolate piping on both sides of the valve (uni-directionally) to vent/bleed the valve cavity between the seats.

Using a single double block and bleed valve system versus 3 separate valves saves installation time, weight on the piping system, and space. It also cuts down the number of leak paths to the atmosphere, reducing the risk of hazards when transferring liquids dangerous to humans or the environment.
 

Double bock and bleed valve specification

Body material: Carbon Steel, Stainless Steel, Alloy Steel.
Normal diameter: 1/2 - 24 Inch (DN15 - DN600).
End connection: Flanged X Flanged,Flanged X Threaded
Pressure range: 150 - 3000 LB/ 15000 PSI.
Working temperature: -46℃ - +350℃.
Structure: (ball/needle/ball), Reduce Bore, One Piece Body.
Design: EEMUA 182, ASME B16.34.
Body Pattern: Three Piece.
Face to face: as per manufacturer's standard.
Test and inspection: EEMUA 182, API 598.
Operation: lever.
 

Double bock and bleed valve application

Double block and bleed valve is most commonly used in the oil and gas industry, but can also be helpful in many other industries.

It's typically used where bleeding the valve cavity is required, where piping needs isolation for maintenance, or for any of these other scenarios:

• Prevent product contamination
• Remove equipment from service for cleaning or repair
• Meter calibration
• Liquid service near waterways or municipalities
• Transmission and storage
• Chemical injection and sampling
• Isolate instrumentation such as pressure indicators and lever gauges
• Primary process steam

How to choose double block and bleed valve?

As with any valve, during selection, one should consider the fluid properties, pressure, temperature. Perhaps most importantly, however, is how the valve will be used. With a number of configurations offered, consider which of these will fit your process and needs best.