What is the purpose by putting 2 ball valves together? And there is a

[Ng Soon Hao]

What is the purpose by putting 2 ball valves together? And there is a gate valve for sampling in between these 2 ball valves. any1 please provide me an explanation thxxx

 

[Q_Goest]

What you're describing sounds like a "double block and bleed". Two valves are put in series on a piping run (block valves) with another valve off a T between them that runs to a vent (bleed valve).

One purpose is to isolate hazardous fluids so that maintenance can be performed safely. The procedure would have both block valves closed and the bleed valve open to vent during any maintenance. That way, if the one block valve leaks back toward where maintenance is being performed, it will go out the vent and you have a second block valve protecting you from this leakage.

I've also seen them being installed where the T has something in it such as a pressure gage or transducer that needs periodic calibration. The two block valves are closed to isolate the component and the bleed valve is used to apply pressure for calibrating the instrument.

Those are the two main reasons I've heard of but there could be others.

 

[Ng Soon Hao]

thx for your explanation, it is very helpful ! =)

 

[NUCENG]

What you're describing sounds like a "double block and bleed". Two valves are put in series on a piping run (block valves) with another valve off a T between them that runs to a vent (bleed valve).

One purpose is to isolate hazardous fluids so that maintenance can be performed safely. The procedure would have both block valves closed and the bleed valve open to vent during any maintenance. That way, if the one block valve leaks back toward where maintenance is being performed, it will go out the vent and you have a second block valve protecting you from this leakage.

I've also seen them being installed where the T has something in it such as a pressure gage or transducer that needs periodic calibration. The two block valves are closed to isolate the component and the bleed valve is used to apply pressure for calibrating the instrument.

Those are the two main reasons I've heard of but there could be others.

Couple of additional applications include common drain or vent that allows either or both tanks to be drained/vented. Another is to provide redundant isolation capability and leakage detection.