Figure 1: One-piece ball valve
A ball valve is a shut-off valve in piping systems, controlling the flow of liquids or gasses. Understanding the differences between 1, 2, and 3-piece ball valves is essential for selecting the right valve for any application. This article examines the design, performance, and specific applications of these ball valve configurations. This article compares 1, 2, and 3-piece ball valves in detail. Read our ball valve overview article for more details on the design and working of ball valves.
In short, the main difference between 1, 2, and 3-piece ball valves is their body design. A one-piece ball valve has only one body portion. Two-piece ball valves have two body components threaded together or bolted together. Three-piece valves, on the other hand, have three independent components.
Building a single-piece ball valve is simple as there is only one body part. The valve trim is attached to the seals through end connections made of the same material as the body. Also, the valve's port size will not be the same as the line size, resulting in a reduced bore design. There is very little or rather no leakage with this type of construction. A one-piece ball valve is irreparable, and it can only be replaced. Figure 1 shows a one-piece ball valve.
One-piece ball valves do not have uses in high-demand industries since they are difficult to repair or replace. In applications where a reduced flow is not a concern, one-piece valves can be employed. Foodservice machinery, liquid filling equipment, and motor fluid filling equipment use one-piece ball valves.
Two-piece valves have two independent components connecting them, either threaded or a bolt and flange assembly. The pieces have body and end connections. As two separate sections are connected, there is the possibility of leaking. As a result, the two-piece ball valve is unsuitable for high-pressure applications. Because of the connection, the valve can be disassembled for internal component repair.
A two-piece ball valve's structure allows it to be used in various applications. The valve can be used with any media because of the ease of maintenance. Food, manufacturing, and automotive industries are just a few of the industries that use two-piece ball valves.
Figure 2: 2-piece ball valve
A three-piece ball valve has one main valve body and two pipe connectors. The pipe connectors are welded or threaded to the pipes. Because of the three-piece structure, the valve body and trims can be removed without interfering with the pipe connections. After installing a 3-piece ball valve, the worn-out components like the ball, seat, or stem can be replaced independently and quickly. It is also more expensive than a two-piece ball valve due to its intricate structure. But, the valve can remain in service for its intended lifespan with low long-term maintenance cost.
The structure of a three-piece ball valve makes it suitable for high-pressure applications where the components experience a lot of wear and tear. The valve is ideal for high-cycle industries since the parts can be replaced and serviced without replacing the entire valve. Primarily, manufacturing industries mainly rely on three-piece ball valves to control liquid flow.
Figure 3: 3-piece ball valve made of stainless steel
Learn more about selecting the right ball valve for your application in our ball valve selection guide.
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Advantages of 3 piece design over 1 and 2 piece design
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(Mechanical)
(OP)
16 Jul 03 02:21Can 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.
(Petroleum)
16 Jul 03 03:231 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.
(Mechanical)
(OP)
18 Jul 03 02:48Thanks 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.
(Mechanical)
18 Jul 03 10:29Provided 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#).
(Industrial)
22 Jul 03 00:03Dose 1 piece and 2 pieces are easier leakage than 3 pieces?
(Mechanical)
24 Aug 03 16:50Lucyn,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.
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