floating ball valve
floating ball valve
(OP)
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





RE: floating ball valve
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: floating ball valve
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
RE: floating ball valve
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
RE: floating ball valve
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
RE: floating ball valve
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
RE: floating ball valve
RE: floating ball valve
I to agree with zdas04 with regards to the sizelimits. I would never use floating ball valves larger than 6"
RE: floating ball valve
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: floating ball valve
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
RE: floating ball valve
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: floating ball valve
RE: floating ball valve
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: Double Piston Effect and Single Piston Effect 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
RE: floating ball valve
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
RE: floating ball valve
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.
:)
RE: floating ball valve
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: floating ball valve
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.
RE: floating ball valve
I believe that everybody here would like a picture of this valve showing its bottom line, the sides and the bleed for sure.
RE: floating ball valve
i wonder what is the point of a cavity drain, if you have no cavity? :D
RE: floating ball valve
Does the following count as a floating ball valve with body bleed to depressurize the cavity?
Source: http://www.chromaticindustries.com/hcv-valve/doubl...
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
RE: floating ball valve
Source: https://www.youtube.com/watch?v=hSIqpzr6nu0
RE: floating ball valve
No it doesn't count. If you look carefully at the first diagram, you can see at the bottom of the ball a little pin. This is the trunnion which olds the ball in place while the seats move to adjust it. The video makes it look like the ball is not perfectly round and that the seats move as it is opened and closed. this might be artistic licence (I like the way the valve contents just drain onto the ground.....?), but does indicate that it is the seats which move, not the ball.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: floating ball valve
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: floating ball valve
Oh I see. The field I'm in (HVAC) did not classify ball valves so strictly so the exposure to different types of almost similar looking ball valve is quite minimal to me. I should also explain that I am just a fresh grad in the business for almost half a year.
Thanks for the info.
RE: floating ball valve