Which is Better: One-Piece, Two-Piece, or Three-Piece Ball Valve?

Ball valves are widely used to control the flow of liquids and gases due to their quick on/off operation, tight sealing, and durability, making them an ideal choice for many applications. Based on the number of separate valve body components, ball valves can be classified into one-piece, two-piece, and three-piece designs. This classification is determined by the design and assembly of the valve body parts, which affects factors such as ease of maintenance, cost, and performance.

1. One-Piece Ball Valve:Structure and Characteristics

The one-piece ball valve is named for its integrated valve body structure. It has a compact design and is lightweight.

The ball, valve seat, and stem are inserted from one side of the valve body. Due to the limited size of the valve body passage, a full bore ball cannot be installed, so the ball passage in a one-piece ball valve is reduced. This limits its flow capacity to some extent. However, it has a cost advantage and is mainly used in low-pressure pipelines.

The one-piece ball valve comes with threaded, flanged, and wafer connections.Threaded connections typically use 55° taper pipe threads, which provide better sealing performance.Flanged connections are easier to install.Wafer connections have a shorter structural length, making them suitable for installation in compact piping spaces.

Common valve materials include WCB cast steel, stainless steel CF8, and CF8M.

One-piece threaded ball valves are mainly used in low-pressure pipelines because the valve stem packing chamber is relatively shallow, allowing for less sealing packing.

One-piece flanged ball valves can be designed as high-temperature drain valves, effectively preventing media leakage from the valve body and avoiding the risk of leakage between the body sections found in two-piece and three-piece ball valves.

These valves can be used for steam and heat transfer oil applications. They can also be made into insulated ball valves, which are suitable for transporting crystallizing or solidifying media. The insulation jacket allows for hot water, steam, or other heat media to flow through to keep the ball valve warm.

2.  Two-Piece Ball Valve:Structure and Characteristics 

The two-piece ball valve consists of a main body and a secondary body, which is why it is called a two-piece ball valve.

This is one of the most commonly used types of ball valves. After the ball, valve seat, and stem are installed in the main body, the secondary body is connected to the main body via threads or bolts. The ball passage is full bore, resulting in low flow resistance and high flow capacity.

Two-piece ball valves are available with internal thread connections, external thread connections, or a combination of both.

The threads typically use 55° taper pipe threads for good sealing. Two-piece flanged ball valves are widely used in various applications.

3.  Three-Piece Ball Valve:Structure and Characteristics 

The three-piece ball valve consists of one main body and two secondary bodies, hence the name.

After the ball and stem are installed into the main body, the secondary bodies are fitted with the valve seats and connected to the main body via bolts, forming a single unit. The ball passage is full bore, providing low flow resistance.

Three-piece ball valves are also available with internal and external thread connections, with internal threads typically using 55° taper pipe threads for excellent sealing. External threads with welded joints allow for direct welding to pipelines. This makes maintenance easier, avoiding the need for separate unions required in internal thread connections.

Butt-weld and socket-weld connections can also use extended pipe fittings to avoid damaging the valve seat seals and stem packing with high temperatures during welding, reducing installation difficulty.

The main feature of the three-piece ball valve is the ability to perform in-line maintenance. By loosening the bolts on the valve body and removing one bolt passing through the main body, the main body can be rotated to replace the valve seat seals. Alternatively, the main body can be fully removed for repairs, while the secondary bodies remain attached to the pipeline, greatly reducing maintenance efforts.

4.Differences Between One-Piece, Two-Piece, and Three-Piece Ball Valves

Body Structure: The one-piece ball valve has a solid body, while the two-piece ball valve consists of two main parts: a body and a cap. The three-piece ball valve is made up of a main body and two end caps, totaling three parts.

Ball Flow Path Size: One-piece ball valves use a reduced diameter flow path, which can affect their flow capacity. In contrast, both two-piece and three-piece ball valves feature full-bore flow paths, offering lower resistance and greater flow capacity. For applications with specific flow requirements, two-piece and three-piece ball valves are preferable.

Installation and Maintenance: Three-piece ball valves are easier to install and maintain compared to one-piece and two-piece designs, requiring less effort. They facilitate the replacement of components such as seat seals and packing.

Procurement Costs: Among the same specifications, three-piece ball valves have the highest cost, followed by two-piece ball valves, while one-piece ball valves are the most economical.

For more information, please contact TFW VALVE, your professional valve manufacturer.