Advantages of 3 piece design over 1 and 2 piece design 1

[tsenthil]

Can any one explain advantages or disadvantages between 1 piece, 2 piece & 3 piece body design in ball valves.

Normally Socket welded/screwed end ball valves are 3 piece in design with most of manufacturer. is it have any specific advantage?

advance thanks for replys.

 

[PeterIgg]

1 piece - few potential leak paths - end connections & stem only. Lighter in weight. Downside is that they can be difficult to repair, especially if they have been installed for a while.

2 piece - only 1 body joint to worry about. Easier to repair than 1 piece valves. Tend to have to remove the whole valve from line (i.e. the end connections have to be unmade). Bulkier and heavier than 1 piece valves.

3 piece - the central body section may be removable without disturbing the end connections. Easy to repair. Central section of valves of the same family from the same manufacturer is often common to various different end connections. Downside is that there are 2 body joints. Low cost, small bore valves tend to use trough bolting rather than studs and nuts. Many small bore (2" and below) low cost 3 piece units do not comply with standards such as ASME B16.34 / BS 5351.

 

[tsenthil]

Thanks for your reply. Please clarify me Is API Specifications talk about Body design?. We are traditionally using single piece valves for LPG Service. My question is

1. Can we use three piece or two piece designs manufactured as per API 607 can be used in LPG service.

 

[Scipio]

Provided there's no local codes prohibiting their use there's no reason you can't use two or three piece designs in that service - make sure you specify they have been fire-tested to 607, however. We use ball valves almost exclusively in gas & oil service, and pretty much every one of them bigger than 2 inches are two-piece designs. As for advantages/disadvantages, PeterIgg's covered everything I can think of.

That said, API 607 doesn't govern ball valve design or fabrication, 607 covers fire testing for quarter-turn valves (which includes butterfly valves).

ASME B16.34 covers general valve design, API 608 covers a limited range of ball valve design (up to 12", flanged 150 & 300# designs, socket weld & NPT up to 600#).

 

[Lucycn]

Dose 1 piece and 2 pieces are easier leakage than 3 pieces?

 

[GGOSCO]

Lucyn,

A 1-piece valve tends to be reduced port product, since the trim needs to be installed through the end connection. Generally they are flange valves and a sleeve is threaded into the port to contain the seats/ball and presses up against an internal seal (some very cheap NPT valves are also 1-piece). These valves tend to be lower end valves, and their level of performance is reflected in the lower cost.

A 2-piece valve is typically used for flanged applications and will be availagle in both full and reduced port. For maintenance the entire valve is removed from the pipeline. The 2-piece design is generally preferred when looking for a flanged valve, as it does have one less leak path when compared to a 3-piece deign. Many chemical producers and refineries have standardized on 2-piece designs for all flanged valves.

A 3-piece valve excels in applications where the end caps are welded or threaded in to the pipeline. The centre section of the valve can be removed from the pipeline very easily and repaired as needed. As well, one of the other advantages is the ability to have different end cap configurations. For example, a 4" reduced port 300# flange could be used upstream and a 3" full port NPT end cap on the downstream. Thus eliminating the need for a pipe reducer and allowing for greater flexibility.

A well designed 3-piece valve can be just as effective as a 2-piece or 1-piece. Generally, the body leakage rate will be irrelevant when compared to the stem leakage rate. Focus on the application and end cap configuration. If it is a flanged valve, look for 2-piece valves, If it is threaded or welded ends, look for a 3-piece valve.

There is no general rule that says all 2-piece are better than 3-piece. It very much dependednt upon process needs and more importantly, the design of the valve. A well designed valve will not leak, a poorly designed product will leak regardless of the configuration.

As for API 607 certification. You will find that all three configurations can be found with a fire-safe rating, however it is much easier to find 2 and 3-piece products.

http://www.ggosco.com