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josej
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Gate Valve

09/17/2013 12:03 AM

Dear All,

We have an existing tank farm installation.Due to government regulations and safety norms we are supposed to put Double Isolation and bleed valve at Inlet/Outlet and recircualtion lines.(6/8/8" Lines) for POL products

Do two gate valve connected in series ,qualify for Double Isolation and Bleed Design

Or

Single plug valve is sufficient

Regards

Jose
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Tornado
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#1

Re: Gate Valve.

09/17/2013 1:06 AM

A single plug valve is not sufficient.

Between the two gate (or other type) valves, there should be a small branch through a bleed valve.

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PWSlack
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#2

Re: Gate Valve.

09/17/2013 3:19 AM

....otherwise it wouldn't be <...Double Isolation and bleed...>, would it?

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IdeaSmith
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#3

Re: Gate Valve

09/17/2013 10:50 AM

What the regulation says!

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bigg
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#4

Re: Gate Valve

09/17/2013 6:40 PM

In any case, there must be a bleed port (routed to an acceptable location) between the two seals. I have seen installations where a single gate valve with a valve body bleed was used (24 - 36" low pressure), but you need to make sure whatever you propose is acceptable to client/government.
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old salt
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#5

Re: Gate Valve

09/17/2013 10:56 PM

josej

A double isolation and bleed valve (Double Block and Bleed Valve) is functionally two valves in series with a small valve tee'd between them. Two valves in series do not meet the qualifications since they do not have the bleed valve between them.

Double block and bleed valve systems are most often used to prevent cross-product contamination or to facilitate maintenance of the valves and other equipment. They are also used to facilitate relief of high pressures. The type of valve be it a gate, disk, ball, etc does not matter. The function- double block and bleed is what determines the name of this system.

A single plug valve does not function as a double block and bleed system since it is only one valve, not the three in a double block and bleed configuration.

Good Luck, Old Salt

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josej
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#6
In reply to #5

Re: Gate Valve

09/18/2013 12:23 AM

Dear All ,

Thanks for the replies.

The proposed plug valve has two sealing arrangement,with bleed in body if one fails second sealing protects ,so two isolation

is this arrangement Double Isolation bleed

Regards

Jose
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Hilton
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#7
In reply to #6

Re: Gate Valve

09/18/2013 2:56 AM

josej,

Your description implies one plug seals twice...I don't think so.

Refer to Tornado and Old Salt...they are correct.

The assembly consist of two independent isolating valves, with a bleed facility (to de-pressurise) between them.

In smaller bore installations (eg instrumentation), the 3-valve assembly is available within a single-cast body. If this is what you meant to describe, and the bleed is between the two plugs it may be acceptable. However, thisw is not generally what is known as double block and bleed.
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Henk klep
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#9
In reply to #7

Re: Gate Valve

09/18/2013 6:54 AM

Guys check the website from control seal.

there are singel valves with a double block and a bleed function (DBBV)

although expensive, but they exsist.

kind regards

Henk klep

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Tornado
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#11
In reply to #6

Re: Gate Valve

09/18/2013 10:00 AM

Why didn't you say that in the first place?

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catman58
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#8

Re: Gate Valve

09/18/2013 6:51 AM

http://www.wermac.org/valves/valves_dbb.html

Hopefully this answers your question. Regards!
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vargaalex
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#10

Re: Gate Valve

09/18/2013 9:06 AM

To do double block and bleed you need two valves in series which will perform the double block and a 90 degree perpendicular valve between the series ones for the bleed part.

The two valves in series must be line sized, gate, block or plug type and the bleed can be up to 25% of the line size since it will bleed only the space between the two valves.

One important thing is to make sure you have the proper rating on the valves.
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11 comments

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Users who posted comments:

bigg (1); catman58 (1); Henk klep (1); Hilton (1); IdeaSmith (1); josej (1); old salt (1); PWSlack (1); Tornado (2); vargaalex (1)

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