Types of ball valves 4

[Unotec]

Good day,

What types of ball valves are there?
Every project we do, we leave up to the mechanical contractor to supply the valves. All we tell him is to use ball valves (service is oil, water, emulsions). Unfortunately this has lead to poor quality valves that seize up quite often requiring more maintenance than the operators are typically willing to do.
Any ideas on how to specify the ball valve type to find something middle range (I wouldn't like to spend too much buying the "Cadillac" valves).
Are there different types of ball valves?

 

[JLSeagull]

Many ball valves are selected for specific applications as engineered items.

Start with engineering standards such as API 6D and ASME B16.34 as the minimum criteria. This will eliminate the valves at Home Depot.

There are full port and reduced port. Normally we buy reduced except for low pressure compressor suctions, pigable valves, etc. The ends are flanged or welded. Flanges are a minimum for line-class block valves. Welded are applicable for acid gas such as the high percentage levels of hydrogen sulfide. Most valves that I buy are NACE MR0175 compliant for sour service - even if the gas is not sour.

Most applications require bi-directional bubble-tight shutoff compliant with API STD 598 and fire safe per API STD 607 or SPEC 6FA, 6FB and 6FC.

Ball valves are available as trunion and floating end. Someone else can explain this better than me.

Offshore we like Zylan bolts and special coatings to keep the valve around for a few years before they rust away.

It is good if the valve is maintainable. That may require lubricating connections etc. Some valves have welded bodies that must be removed and sent to the shop instead of serviced in the field. I forgot to mention top entry valves that may permit service with the body in the line.

Elastomers have to be compatible with the fluid. Some absorb CO2 then explosively decompress. Some are eaten by amine, etc.

...

Stay away from those Cadillac valves.

 

[Unotec]

Thank you.
I use full port ASME/ANSI B16.34 valves. To be more specific, I would like to know if, in the design of the valve, there is something I can specify that will keep me away from poor quality valves. Something with the seats, or something
BTW, trunion valves are a little expensive here. I am doing some research on the ones with purge port but they also seem quite costly

 

[Ashereng]

There are good valves and bad valves. There are good cars and bad cars. There are good ... and bad .... The trick is the right valve for the application.

There are two common types of ball valves, floating ball and trunnion. There are others (eg. the Orbit valve) but I will leave that for now.

If quality is the issue, I usually supply a list of acceptable manufacturers to my contractors, say "I will accept ball valves of up to 8" from the following: Grove, Nutron, KF, and no other". By the way, these are just examples - I am not meaning to recommend one manufacturer over any other.

"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?

 

[Unotec]

Thanks, this is what I was thinking of doing.
I could not find a design specification that would differ from a good valve to a bad valve. I am not confortable creating guidelines with brend names, but in the valve market I think is inevitable. And in all fairness, if good manufacturers have developed their products up to those standards it is only fair to recommend them.

 

[Ashereng]

Yup. That's why many people buy "put name brand here".


"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?

 

[zdas04]

There are several threads in this forum on the difference between trunion and floating ball valves, but breifly:

- Floating Ball Valves: The ball floats in the space available for it and differential pressure will push the ball into the downstream seat. This leaves the body cavity pressurized on a shut valve. Floating ball valves work pretty well when there is a definate pressure directionality from one side of a shut valve to the other. If the direction of the dP changes there will be a time when the ball has to float from one seat to the other and can pass considerable fluid during that transition.
- Trunion Ball Valve: Both seats are spring-loaded to push them against the ball which is held in place by a pair of trunion bearings. These valves are good for any dP scenario. When the valve is shut, a body bleed can be opened to evacuate the body cavity. Many companies find this to meet the definition of Double Block and Bleed.

As to manufacturers you want to look to someone who has local sales and support. Where I live, Zy-Tech PBV is well repped, but so is WKM and KF.

David

 

[JimCasey]

Usually floating ball valves are in the lower-pressure classes with resilient seats but with extrusion-resistant polymers the valves are offered up to around 6000 psi. As long as the valve relies on polymeric seats, the temp limit of the valve will be defined by the polymer. Embellishing a bit on what zdas04 stated above: floating ball seats are usually flexible and preloaded (crushed) against the surface of the ball. This way they shut off at low pressure differentials and although the ball is designed to be able to move into the downstream seat, the actual travel is pretty small. Most of the time, both seats seal. This can trap high pressure liquid inside the ball and cavity, and for cryo liquids, Chlorine, etc. it is necessary to drill a hole in the upstream side of the ball to release the pressure generated if the liquids vaporize. A good supplier will have developed mind-boggling arrays of seat technologies for various materials, pressures, temperatures, and other applications criteria.

Valves without elastomers can work at elevated temperatures; Valvtechnologies and Mogas use hard alloy balls and a hardfaced seating surface in the body, and the ball is lapped to the seat. Generally the ball is loaded against the seat by a spring mechanism/belleville washer and these valves are unidirectional, but just the ticket if you want to isolate superheated steam.

A 6" Ball weighs around 200 pounds. That's a lot to support on two polymer seats. Trunnion valves have an advantage for higher pressure valves as well as larger size valves. The seats, as mentioned earlier, are spring loaded against the ball(springs, belleville washers, even o-rings are used) AND the upstream area of the seat is larger than the downstream area of the seat so that increasing process pressure loads the seat against the ball. The loading mechanism pretty much dertermines how much crud the valve can tolerate: O-rings are used for paper stock, but coil springs can be used on clean steam. Trunnion valves can have seats with polymeric inserts, or the seats can be metallic for extended pressure/temp range.


Refer to my granite slab which bears the engraved message: There is a best valve for every application.

 

[StoneCold]

unotec
Something that you might consider is going out and buying multiple valves from multiple venders and see which ones hold up the best. One thing that I have done that has helped my ball valve situation is that instead of specifying virgen teflon seats I now request reinforced teflon seats. I tend to get less seat blowouts now. Maybe this will help you as well.

Regard
StoneCold

 

[NGiLuzzu]

StoneCold,
I agree with the method you propose.

In addition, about the PTFE-realted issues, may be you'll find interesting to take a look at thread408-163021 and thread408-166397 within this Forum...

Best Regards, 'NGL