Single Block and Bleed Ball Valve??

[onrush]

Dear members,

Our client of current project requires single block and bleed ball valve.
I am familiar with double block and bleed ball valve that has two levers and balls with bleed.
But, I am not familiar with single block and bleed ball valve.
Can anyone tell me about single block and bleed ball valve?

Thank you in advance...

 

[minty]

Hi there Onrush,

With regards to single block and bleed valves, you can either install as two separate valves (i.e. a block valve with a bleed drain downstream in the pipework) or you could install an integral single block and bleed unit. I am not hugely familiar with these but a quick search on Google revealed the following link, which should give you a starting point:

http://www.sabre-valves.com/Double_Block_&_Bleed Valves.htm

Scroll to the "BSBBX" model and compare with the double block and bleeds on the page.

Here is the Google search I used:

http://www.google.co.uk/search?hl=en&q=single+block+and+bleed&meta=

Finally, you could always talk with any block valve manufacturers - they should be able to tell you all you need to know.

Hope this helps!
Michelle

 

[pennpiper]

Your Client may be requesting the use of a single Gate valve with a "split" wedge and the tap at the bottom canter of valve body drilled out and fitted with a bleed valve.
This was done on one of my projects long ago. I think it was a Crane valve.

 

[zdas04]

Why are you asking here? All we can do is guess (my guess is that they mean OSHA Double-Block-and-bleed capability all in one valve body, but I'm just guessing too). Call you client and tell them that their terminology is foreign to you and ask if they have a picture, web-site reference, manufacturer, or any other information. If you assume that one of us has guessed right, then you could be in real trouble if you spec something like a split wedge gate valve when they really wanted a trunnion ball valve or a DBB valve with two handles.

David

 

[lizking]

Here's another guess: search for Cooper Cameron Twin Seal valves.

 

[donf]

onrush,

Google "downstream vent valve".

Here's one link:

http://www.swagelok.com/downloads/webcatalogs/EN/MS-02-28.PDF

The downstream vent version is commonly used to vent stored energy in pneumatic systems. When the valve is closed - air to the tool or hose is vented so that it can be disconnected or worked on safely. One application of the upstream vent version is as a steam trap test valve. When valve is closed, upstream steam/condensate is vented and observed.

In the plumbing industry, they're referred to as "Stop and Waste" valves.

I suggest getting a written description of the required valve function from your client.

Hope this helps.

Donf

 

[pasta1993]

I can help you for double block & bleed valve.

 

[MortenA]

More guessing:

Some mistakenly thinks that a trunnion mounted ball valve with a bleed inbetween the seats has a DBB function because you can test the integrety of the seals using the bleed. But both seats are only tight if there is the same pressure upstream and downstream the valve.

Best regards

Morten

 

[Ashereng]

Morten,

I am a bit confused by your statement of "But both seats are only tight if there is the same pressure upstream and downstream the valve." I would have thought that the spings on the seats would provide sufficient seal on lower pressure side of the valve.


"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[MortenA]

Ash

If you dont bleed the cavity (or the upstream seals leaks and the bleed is closed following a "bleed" then theres only the spring on the low pressure side (if theres a high pressure on one side on the valve and atmospheric on the other side - and my source (textbook) says thats not enough to provide a tight seal if the upstream seal leaks.

Maybe its old/too conservative?

Best regards

Morten

 

[Ashereng]

MortenA,

Ahhh, your scenarios is a bit different.

On a "working" valve, the upstream seal usually is aided by line pressure to seal against the ball. If the line pressure is low, then the springs aid to seal against the ball. This is also true of the downstream side.

So, a trunnion ball with spring seals, can hold the upstream line pressure, even with atmospheric downstream line pressure.


Now, "IF" the upstream seals fail, will the downstream seal hold? That is the $64,000 question. And, also why I personally use 2 valves for double block and bleed applications. In this case, as your textbook states, the downstream seal may not be enough to hold the upstream line pressure.

In this case, also, the valve has been damaged - and is not a "designed" or "normal" condition, and hence, not a "fault" or "weakness" of the trunnion with spring seals design.

I hope this clears it up a bit.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?