LET'S TALK ABOUT EXACTLY WHAT IS A DOUBLE BLOCK AND BLEED VALVE?
In my experience, double block and bleed always seemed like a leave the Cobra Kai karate dojo. Obviously, a dual block and bleed valve are not related to karate, it's more details on controlling process flow to match maintenance, sampling, and flow diversion. This publication describes the features of a dual block and bleeds valve, its function, and application.
Exactly what is a double block and bleed valve?
A dual block and bleed valve (DBB) are much like getting three valves in a single.
API 6D defines a dual block and bleed valve like a "single valve with two seating surfaces that, within the closed position, supplies a seal against pressure from both sides from the valve having a way of vending/bleeding the cavity between your seating surfaces."
There's a couple variation of double block and bleed valves. One style, such as this one from J-Flow Controls, has two individually seating valves inside, having a bleed or drain valve. This configuration is called a dual isolation and bleed (DIB). The DIB valve can isolate each side from the valve (bi-directionally) to vent or bleed the cavity and isolate piping.
J-Flow Double Block and Bleed Valve
This trunnion style ball valve from Val-Matic provides double block and bleed in one valve. This style can isolate piping on sides from the valve (uni-directionally) to vent/bleed the valve cavity between your seats.
Val-Matic Double Block and Bleed Valve Quadrosphere
Utilizing a single double block and bleed valve system versus 3 separate valves saves installation time, weight around the piping system, and space. Additionally, it cuts lower the number of leak pathways towards the atmosphere, reducing the chance of hazards when transferring fluids harmful to humans or even the atmosphere.
Which applications need a double block and bleed valve?
Double block and bleed valves are most generally utilized in the gas and oil industry, but may also be useful in lots of other industries.
It's typically used where bleeding the valve cavity is needed, where piping needs isolation for maintenance or these other scenarios:
Prevent product contamination
Remove equipment from service to clean or repair
Meter calibration
Liquid service near waterways or municipalities
Transmission and storage
Chemical injection and sampling
Isolate instrumentation for example pressure indicators and level gauges
Primary process steam
Things to look for when choosing a dual block and bleed valve?
Just like any valve, during selection, you ought to think about the fluid qualities, pressure, temperature. Possibly most significantly, however, is when the valve is going to be used. With numerous configurations offered, consider which of those will match your process and requires best.
If you are unsure which double block and bleed valve fits your needs process, speak with an engineer. They are able to help pick which you will achieve your objectives best.