floating ball valve 3

[engahmedbahgat]

good afternoon, I have a question about floating ball valve, when this valve is closed, the pipeline upstream pressure pushes the ball against downstream seat ring to attain tight seal, at this case I imagine that the ball as pushed toward downstream seat, it pushes away from upstream seat, so the valve cavity will be connected to pipe upstream pressure and if I trying to open body bleed to depressurize the cavity, it won't be depressurized, it that true or not? and what will be the case in open positions? thank you in advance

 

[zdas04]

Only one thing wrong--floating ball valves do not have body bleeds. They would be worthless because the upstream side of the ball is not even touching the seat.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[engahmedbahgat]

thank you "zdas04" for attention, but I have in my site a floating ball valves with body bleeds, how can I explain that?
also I want to ask about open position in floating ball valve, is the upstream seat will be in contact with the ball in case of open positions? is that true, we can explain the existence of body bleed by saying, it works while valve in open position

 

[zdas04]

No, you don't have floating ball valves with body bleeds. My guess is that what you are seeing as "body bleeds" are actually grease ports to inject seal fluid (they have internal ball check valves to prevent them from becoming body bleeds). If you actually do have body bleeds then the valves are trunion, not floating.

When a floating ball valve is open, the ball floats between the two seats, but the "force" of friction tends to push the ball against the upstream seat. The downstream side of the ball is off the seat so the body cavity is always pressurized.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[engahmedbahgat]

thank you very much "zdas04", I will check again according to your clarifications,
I want to ask you about other points please
- how can I differ between floating and trunion, in other word, the trunion place should be appear below the valve, or it can be inside the body and I cant see it when looking under the valve, generally how can I differ between two types?

- is there any limitations about floating and trunion mounted sizes?

- the valves which I talking about are old valves, installed from about 20 to 30 years, is our discussion about body bleeds can be applied on them, in other word, if these old valves have body bleeds, then they are trunion?

thank you again for honest help

 

[zdas04]

Trunion ball valves have trunions and trunion bearings. You can often identify the trunion bearing on the bottom of the valve, but sometimes they are pretty hard to see. I generally look for a body bleed to tell for certain.

There doesn't seem to be an upper limit in size for trunion ball valves, the smallest I've ever seen is 2-inch (DN 50). I've seen floating ball vavles from 1/4 inch (DN 6 I think). I won't buy a floating ball valve much bigger than 4-inch, but I've seen them in 30-inch. I don't know if larger sizes are available or not.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[engahmedbahgat]

thank you very much "zdas04" for attention and valuable information,

 

[Kreot]

It depends on the seat configuration. If you have floating seats, the pipeline pressure will push the upstream seat towards the ball and you will have a double isolation. Take a look at the valve drawing, or you can verify the tightness of the upstream seat through the cavityvalve. Both floating and trunnion ball valves can have cavity drainvalves.
I to agree with zdas04 with regards to the sizelimits. I would never use floating ball valves larger than 6"

 

[LittleInch]

Err, yes the upstream seat will seal, but the downstream seal for single piston effect seals will only withstand the pressure required to overcome the seal spring force, generally quite a low pressure so I would never describe that as "double isolation" As zdas04 has very well stated, floating balls operate in a different manner and hence the cavity drain, if indeed there is one, is only there to drain the valve for removal, not to prove the upstream seal because it doesn't have one, only a d/s seal.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

LittleInch,
What brand of floating ball valve has a cavity drain? I thought I was familiar with all the major suppliers and none of the brochures that I have show a cavity drain on a floating ball valve. Sounds like I'm missing a set of brochures.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[LittleInch]

I did say "if indeed there is one" as other posters seem to believe they exist. I've never seen one either....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Kreot]

Do have a few floating ball valves (with single piston seats) in our plant, with cavity drain. We use some as double isolationvalve, but to do so you need a cavity drain regulate the pressure in the cavity. It might not be a standard from any supplier, but they do exist. As long as the upstream pressure is sufficient to push the ball to the d/s seat and the u/s to the ball i do not see any reason for not using this as a double isolation (even though the main seal is d/s)

 

[zdas04]

I do have a real problem with floating ball valves in positive energy isolation. Let's say we are doing double block and bleed between a source that will remain pressurized and a sink that is open for hot work. I start by shutting the two valves and opening a vent (creating a "vent chamber"). The upstream valve sees a significant dP and the ball is pushed hard enough into the downstream seat to have an excellent chance of a seal (but leakage is of course possible). With the work area pressurized and the downstream valve shut, the side of the downstream valve (actually the upstream side relative to the work) is pushed hard on the chamber-side seat. Then the work space is blown down. The downstream valve has the vent chamber at atmospheric pressure and the downstream piping also blown down--dP is zero, there is no energy source to cause the ball to be in any position. When the dP is at zero, the ball will move to a rest position, off of both seats. If the upstream valve leaks, some of the gas will blow through the downstream block because there is no energized seat. Most will likely go up the chamber-vent, but some will enter the work space. This is rarely dangerous, but it occurs often and the intermittent puffs of flammable gas is pretty annoying (and is more dangerous by contributing to an oxygen-deficient environment than a major fire/explosion hazard).

I use trunion ball valves for DBB in any jurisdiction/company that allows them. Having two energized seats makes a lot more sense to me than 2 floaters (which is legal everywhere and every company even if it isn't actually safe).

Everything I know and can find (see thread408-205580 for example, the links don't work, but the last description is good) says that in a floating ball valve the seats are fixed (no "piston effect" in a floater). If you have single-piston ball valves with "cavity drains", then you also have trunion bearings.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[LittleInch]

Stiaf,

You must have some weird valves - I took the text below form a valve vendors web site and certainly clues in with my understanding of floating versus trunnion mounted valves... If you actually have floating seats then the d/s seat must be being squashed hard against it's seat slot due to the high force. Can you let us know which make and model this is.

The key difference between a floating ball valve and a trunnion mounted ball valve is how each achieves a line seal. Trunion mounted ball valves are uses a spring mechanism and/or line pressure assistance to drive the upstream seat against the stationary ball. The surface area exposed to the pressure through the relatively small passageway is actually just the back of the seat.

The floating ball valve utilize natural line pressure to press and seal the ball against the downstream seat. The line pressure is exposed to a greater surface area - the entire upstream face of the ball, which is an area equal to the actual pipe size.

A floating ball valve is a valve with its ball floating (not fixed by a trunnion) inside the valve body, it drifts toward to the downstream side and tightly pushes against the seat under the medium pressure to ensure sealing reliability. The floating ball valve has simple structure, good sealing performance but the seat material is required to withstand the workload since the sealing pressure is bared by the seat ring. Due to unavailability of high performance seat material, floating ball valve is mainly used in middle or low pressure application.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Kreot]

Hi,
I am not to say if the valves are weird or not. I do agree with you that high pressure larger floaters are not suitable as a double sealing, not only will the force of the ball damage the seat, but it will also affect the integrity of the stem.
This is a 4" low pressure valve with a pipe OP of approx 25barg. I see that 2 of the valves are from italy (PV) and one from Oliver. the latter one not funtioning- If they have been customized i do not know...even though we seldom do maintenence downstream this valves we use a pressure indicator on the cavitydrain, and a pressure indicator downstream the valve to check the integrity of the seats. We do need to have surveillance of the cavity pressure to make sure that the sealing is ok...we also need to test both barriers before starting maintenence. Most of our double isolation valves are gatevalves, but we do also have som SR/DP trunnion.

In our company(Oil&Gas company) we can use floaters with springloaded seats as double isolation as long as we do have a cavityvalve for pressure surveillanc, and of course all other precatuions is taken.

From my experience as an operator i do have many pros and cons for both trunnion and floaters (as i guess you will find/or see if you start a discussion regarding the topic), but valves is always nice to discuss, even though i see many different opinions.

 

[zdas04]

Spring loaded seats require a rigid ball. They just don't work on a floating ball (they don't have enough travel). If you have spring loaded seats, you have a trunion. Every time.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[trvalve]

Hello,
Previously worked for valvemanufacturer in Asia ,now in Europe. This is a very interesting discussions, and in my opinion you all have good points. Both the companies i worked for have designed floating ball valves with floating seats, tested to give double isolation (or DBB as many say). They were specified by customer , so the seat was design for this and tested. They also had bodydrain valves..so yes, they do exist. They fullfilled the purpose as far as i know, even though maybe it is not the best choice. Think they were sold to australia and europe british sector.

 

[Roberto1956]

As trvalve said and I believe that it is not difficult long time ago a valve to be made without any standard. Nowadays company does what client ask to keep their profit and they deliver warning that it is not according to standard.
I believe that everybody here would like a picture of this valve showing its bottom line, the sides and the bleed for sure.

 

[mbelly84]

yes, me also i'm very interested to see these floaters with cavity drain capability.
i wonder what is the point of a cavity drain, if you have no cavity?

 

[SkyeTan]

Came across this post while researching for something else.

Does the following count as a floating ball valve with body bleed to depressurize the cavity?

Source:

http://www.chromaticindustries.com/hcv-valve/double-block-and-bleed/

At this point of time, this post is just for self-satisfactory purposes to see if what I comprehended is likely the thing posters have in mind.

Cheers,
Tan