What is the P&ID symbol of a double block and bleed valve (DBB) (Not two independent valves and a bleed valve) ?

[wbic1]

Is there a P&ID symbol for a double block and bleed (DBB) valve being used on a P&ID? I am not asking for symbols which show two seperate valves and a bleed valve. The symbol I am looking for is one symbol which represents a DBB valve.

 

[pierreick]

| What is Piping

Double Block and Bleed Valve is a single assembly of two inline block valves and one bleed valve.

whatispiping.com

another symbol in the link underneath:

Piping and Instrumentation Diagrams - P&ID Symbols

P&ID Symbols for Valves, Equipment, Instrumentation. Piping and Instrumentation Diagram Valve Symbols for Standard and Smart Systems

lasersurveying.com

Whatever symbol chosen you will need to notify the reader .

Pierre

 

[LittleInch]

First you need to define what you mean.

The terms used are often quite interchangeable unfortunately.

Officially a double block (DB) valve is one which can seal from both directions. This comes from I think API 6D

Double block and bleed valves as single units do exist, but are really DIB valves. Achieving this with a ball valve requires double piston effect seals (DPE) and many people think the sealing in reverse is very marginal. Only expanding gate or plug valves can do this to high level of reliability.

So on a P&ID I would normally expect this to be the valve symbol and letters under it saying DBV or DIB. Then you can add a special detail if needed to show where the drain/vent or pressure relief goes to.

Those smaller units made from one casting I would show as three valves and the add a dashed box around the three of them and another or state DBB under the box.

As said DBB has an unfortunate tendency to be splashed around without people necessarily understanding what they mean when they say it.