Can a Floating Ball Valve be installed in any direction 3

[VVman1]

Can a Floating Ball Valve be installed in any direction, is there a perfered direction for flow? I am under the impression that a Floating Ball Valve is Bi-Directional. I was told that I must use a Trunnion Ball Valve for Bi-Directional service. There are no indicators on the valve body as to the direction of the flow. I have looked at many manufactures and NONE of them have a perfered direction. My valve is a 4" 150#, C/S, R/F F/P to the design standards of API-608. I am of the understanding that a Trunnion valve per API-6D is designed for Double Block & Bleed and it too can be installed in any direction. HELP me please with this question.

 

[zdas04]

Floating ball valves are bidirectional. The right-hand seat is identical to the left-hand seat so going to the left is just the same as going to the right. In very low dP applications I prefer vertical down to vertical up, but I have installed hundreds of small floating ball valves in vertical-up vent service with less than 3 psid that have worked very well with leaks being rare so this is probably more "fear and superstition" than a real data point.

In my interpretation of the OSHA definition of double-block-and-bleed, a trunnion ball valve satisfies the requirements. I do work for several companies that adamantly disagree with my interpretation. At the end of the day, company policy determines whether a trunnion ball valve satisfies their risk tolerance for DBB.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"Life is nature's way of preserving meat" The Master on Dr. Who

 

[gerhardl]

My interpretation:

Question 1. Yes, for any good construction. Weak constructions may always be weak in one way or another.

Question 2. No.

A double block and bleed is in my opinion constructed to block any amount of fluid ,including gas increasing pressure by higher temperature, caught in the room between the seals on both sides and the ball, from escaping to the pipeline both (and either) upstream or downstream.

Bleed construction only if equipped with bore (bore may be plugged by threaded plug or equipped with drainage valve or contraption) to bleed off extra fluid and/or pressure in room above.

Trunnion mounted in itself is no guarantee for either. On the other hand it has to be a trunnion mounted construction to fulfill the requirements.

The description of block and bleed should always be followed by detailed description (not only a norm) of how the end user require this to work (fluid, pressure, lifetime, operation mode, other details and norm etc. etc).

 

[zdas04]

Gerhardl,
Your reply was amazingly cryptic.

If the first question is his post was "Can a Floating Ball Valve be installed in any direction, is there a preferred direction for flow?" then are you saying "Yes it can be installed in any direction" or "Yes there is a preferred direction for flow"? And what the heck does "Weak constructions may always be weak in one way or another." mean? I can't find anything in the original post that that answers.

There is only one question mark in his post so I'm having trouble finding Question 2.

The comment

Trunnion mounted in itself is no guarantee for either. On the other hand it has to be a trunnion mounted construction to fulfill the requirements.

doesn't make sense to me. Nothing in any DBB regulations that I've ever seen requires a pair of trunnion valves with a vent. They all talk about a pair of seating surfaces separated by a vent adequate to handle possible leakage. The body bleed and spring loaded seats in a trunnion ball valve satisfies all of these requirements in my opinion.

David

 

[gerhardl]

I apologize, please let me try to be a bit more exact:

Answer to o your question mark:
Yes, a floating ball valve can be mounted in any direction. No, there is no preferred direction of flow, either way and not depending on how the valve is mounted.

The answer is based on the presumption that you have a valve with good and precise construction and quality, not from some backyard producer without proper quality control and testing.

In my opinion it is not necessary with a trunnion mounted ball for this application, (but a trunnion mounted might have a longer overall lifetime.)

The rest (comment on how to understand a double block and bleed compared to a trunnion mounted construction only) is only meant as a coment to Zdas04.

OK?

 

[zdas04]

Thank you.

David

 

[JimCasey]

There ARE floating ball valves that are unidirectional.
One example: the severe service types such as Mogas or VTI. Upstream is basically an energizer and the ball floats into a lapped seat for shutoff.

Other unidirectional ball valves are chlorine or cryo valves that have a relief hole to vent liquid gas upstream from the cavity if it warms to above its saturation pressure and vaporizes. It is inadvisable to vent downstream because when the ball floats against the downstream seat with shutoff differential, it can unload the upstream seat. If the upstream seat leaks, then the relief hole completes the leak path if pointed downstream.

The vast majority of floating ball valves have identical construction upstream and downstream and are fully omnidirectional.

 

[zdas04]

JimCasey,
You're right. I've even seen them in upstream Oil & Gas (we use drilled balls for tank load-line valves to prevent the trapped water from freezing). My experience has been that unidirectional valves have a somewhat different name (e.g., V-Ball, Anti-Freeze Ball Valve, etc.) so you have to be pretty specific on your order to get a unidirectional ball valve.

David

 

[MortenA]

Re DBB and trunnion mounted valves:

A trunnion mounted valve can be fitted with a cavity bleed valve that enables that the seat tightness can be tested. Some valve vendors will efer to this as DBB (using only one valve). It is however NOT true DB since the valve seats on is tight if there is high pressure on both sides of the vave. So if you have a significant pressure difference upstream/downstream and you close the bleed and the HP side fails - the it will push the LP seat open. If the reason for requing DBB is that you have opened the line then downstream pressure will be atmosperic and then you wont have DBB at all - open or closed bleed.

Best regards

Morten

 

[MortenA]

I can see that my oppinion had already been posted. Sorry about that.

Best regards

Morten

 

[zdas04]

MortenA,
It really is an interpretation issue. I've never seen a Trunnion Ball Valve that did not have a body bleed. Not once. When I write procedures for isolation for hot work I specify that the valve is to be shut, the body cavity blown down and then the bleed assembly is to be removed, placed in a bag and locked to the valve. I've used this procedure for upwards of 100 projects that required hot work and have never had an issue.

The term "True Double Block and Bleed" is a marketing ploy by the guys that make the dual plug valve monstrosity that is (in my opinion) less secure than a trunnion ball valve because it doesn't take much trash to keep a plug valve from sealing since the plugs and seats are non-resilient.

As I said above, satisfying a regulatory requirement for positive isolation becomes the responsibility of the company and their tolerance for risk. The company that I used to work for didn't have a policy when I was there so I was free to perform my own risk assessment. they have a policy now and as I understand it a Trunnion Ball Valve is no longer considered adequate DBB at that company. A bunch of us Cowboys spent a lot of money on Trunnion valves and then retired and our replacements either don't understand or don't accept our rationale.

David

 

[moltenmetal]

I always thought that part of DBB isolation philosophy was to ensure that a singe dumb operator action (i.e. operating a single valve handle)was insufficient to lead to a catastrophe, and obviously a single trunnion wouldn't do the job. I've seen situations where all you wanted was positive isolation against trace through leakage, and the trunnion with cavity vent is a good idea for that.

 

[zdas04]

I always thought that the "Lock Out" part of "Lock Out/Tag Out" was there to prevent a dumb operator action. If I lock a valve shut and keep the key safe from dumb, then it takes a really strong dumb-operator to override it.

David

 

[MortenA]

zdas04

But then its a question of wether you NEED DBB or not. In my oppinion you dont get double block from a signle trunnion mounted valve (and i dont sell valves) - and would not recommend plug valves especially. You need the positive dP for the seal and you wont have that on the downstream seat.

The usual DBB would be two block valves with a seperate bleed valve in-between. The only advatage with plug valves in relation to DBB will be that some manufactore provide a DBB that will fit into a standard API valve dimension. But i think i mentioned this before. That is only relevant for retrofit.

But then again im not a big fan of DBB. Usually its recommended for parallel operating trains with 900# rating and above. But that differs slightly. In my oppinion DBB wont help agains operator faults. If he opens one valve - then he will continue to open the second one also i think.

Best regards

Morten

 

[zdas04]

Morton,
The only time I know of that you are required by law to have "positive energy isolation" under OSHA in the US is for hot work downstream of a flammable fluid. The techniques that satisfy this condition are blind flanges, insert blinds, disconnecting and misaligning pipe, and double block and bleed. OSHA goes on to say that DBB is not suitable for hot work in a confined space. I think that a Trunnion Ball Valve satisfies this particular requirement in the regulation.

There are also process reasons for DBB. One that I've often used is when people insist on a meter station bypass. When it is my gas being sold I only accept a meter station bypass if they have DBB with the valve(s) locked (or sealed) shut and the bleed open and verifiable. Trunnion valves work better for this than two ball valves and a 2-inch vent because you can see smaller quantities leaking through the bleed port.

I know that inside plants there are other reasons for DBB and maybe they have specific process requirements that make the Trunnion Ball Valve inappropriate, but I don't work in plants and don't know much about them.

David

 

[MortenA]

I never work in the US - and mainly in plants. There are no legal requirements as far as i know e.g. offshore in the north sea - but i know a lot of operators seems to fancy them.

I have often heard the "safety from false opening" argument. But my feeling is that if an operator think its OK to open one valve to get gas7Liquid flowing he will also open the next valve. But for maintenance on parallel trains (HP e.g. #900) then it may be justified i guess.

Btw i dont think the trunnion mounted ball valve is inappropriate just that it wont provide true DBB - at least by some operators view (but you already agreed to that last point - altough not to the point of view )

Best regards

Morten

 

[zdas04]

HSE in the UK has all the same "keep 'em safe in spite of themselves" attitude as OSHA. I'd be amazed if there isn't a regulation in the UK about "positive energy isolation" for hot work.

What satisfies DBB is absolutely up to each operator's risk tolerance.

David