What is the difference between a one piece and two piece ball valve?

You need a cost-effective ball valve, but the choices are confusing. Selecting the wrong type means you could be stuck with a permanent, unfixable leak when it eventually fails.

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The main difference is construction: a one-piece valve has a solid, seamless body, while a two-piece valve has a body made from two parts screwed together. Both are considered non-repairable, throwaway valves meant for simple applications.

This might seem like a small technical detail, but it has big implications for a valve’s strength, flow rate, and potential points of failure. It’s a fundamental concept I always review with my partners, like Budi, a purchasing manager in Indonesia. He needs to provide the right valve for the right job, whether it’s for a simple home project or a demanding industrial system. Understanding how these valves are built will help you decide which one fits your needs, and when you should step up to a more professional solution.

How does the construction of a 1-piece vs. 2-piece valve affect performance?

You see the seam on a two-piece valve and worry it’s a weak point. But then you wonder if the seamless one-piece design has its own hidden disadvantages.

A one-piece valve’s solid body has no seams, making it very robust. However, it usually has a reduced port. A two-piece valve can offer a full port but introduces a threaded body seam, creating a potential leak path.

The performance trade-off comes directly from how they are made. A one-piece valve is simple and strong, but the ball must be inserted through one of the ends, which means the ball’s opening (the port) must be smaller than the pipe connection. This restricts flow. A two-piece valve is built around the ball, so the port can be the full diameter of the pipe. This is its main advantage. However, that body seam, held together by threads, is a critical point of potential failure. Under stress from pressure spikes or water hammer, this seam can leak. For a buyer like Budi, the choice depends on the client’s priority: the absolute structural integrity of a one-piece for a low-flow application, or the superior flow rate of a two-piece, with its associated leak risk.

Performance at a Glance

Feature One-Piece Ball Valve Two-Piece Ball Valve Body Integrity Excellent (No Seams) Fair (Has a threaded seam) Flow Rate Restricted (Reduced Port) Excellent (Often Full Port) Repairability None (Throwaway) None (Throwaway) Common Use Low-cost, low-flow drains Low-cost, high-flow needs

What is the difference between a one piece and three-piece ball valve?

Your project demands long-term reliability. The cheap one-piece valve is tempting, but you know the downtime from cutting it out to replace it will be a disaster.

A one-piece valve is a sealed, disposable unit that is permanently installed. A three-piece true union valve is a professional-grade solution that can be fully removed from the pipeline for easy repair or replacement without cutting pipe.

This is the most critical comparison for any professional application. The entire philosophy is different. A one-piece valve is designed to be installed once and thrown away when it fails. A three-piece valve is designed to be a permanent part of the system that can be maintained forever. I always share this with Budi for his clients in aquaculture and industrial processing. A leak in their systems can be catastrophic. With a one-piece valve, they face a prolonged shutdown for a messy replacement. With a three-piece Pntek true union valve, they can unscrew the two union nuts, lift the valve’s body out, pop in a replacement body or a simple seal kit, and be running again in five minutes. The slightly higher initial cost is paid back hundreds of times over by avoiding a single hour of downtime. It is an investment in operational efficiency.

What exactly is a one-piece ball valve?

You need the absolute lowest-cost valve for a simple job. The one-piece design looks like the answer, but you need to know its exact limitations before you commit.

A one-piece ball valve is made from a single, solid piece of molded plastic. The ball and seats are inserted through the end, and the stem and handle are fitted, creating a sealed, non-repairable unit with no body seams.

This construction method gives the one-piece valve its defining characteristics. Its greatest strength is having no body seams, which means one less place to leak. It’s also the simplest and therefore cheapest to manufacture. This makes it a great choice for non-critical, low-pressure applications where it won’t be operated often, such as a basic drain line. However, its major weakness is the “reduced port” design. Because the internal components have to fit through the pipe connection hole, the opening in the ball is smaller than the pipe’s internal diameter. This creates friction and reduces the overall flow rate of the system. I explain to my partners that these are perfect for their retail customers doing simple DIY projects, but they are not the right choice for any system where maximum flow and serviceability are important.

So, what defines a two-piece valve?

This valve seems stuck in the middle. It’s not the cheapest, nor is it the most serviceable. You’re left wondering why it exists and what its specific purpose is.

A two-piece valve is defined by its body, which is made from two sections that screw together. This design enables it to have a full-sized port at a lower cost, but it creates a permanent, non-serviceable body seam.

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The two-piece valve was created to solve one problem: the restricted flow of a one-piece valve. By making the body in two halves, manufacturers could assemble the valve around a larger ball with a full-sized port, matching the pipe’s internal diameter. This provides excellent flow characteristics at a price point below a three-piece valve. This is its only real advantage. However, that advantage comes at a cost. The threaded seam that holds the two halves together is a potential weak point. It’s not designed to be taken apart for service, so it is still a “throwaway” valve. For my partners, I frame it as a niche product. If their customer absolutely needs full flow but cannot afford a three-piece valve, the two-piece is an option, but they must accept the increased risk of a leak at the body seam over time.

Conclusion

One-piece and two-piece valves are both non-serviceable designs. The best choice depends on balancing flow rate (two-piece) against body integrity (one-piece), and both are inferior to a three-piece valve.

Post time: Aug-06-

What Is a Ball Valve?

A ball valve is a quarter turn shut-off valve that controls the flow of fluids by a rotary ball. The spherical rotary ball consists of a straight bore through it. The pipe is in the open position when the bore is aligned in the same direction as the flow, allowing the fluid to pass through it. When the bore is rotated 90 degree from the flow path, the valve is closed, and the flow is blocked. Ball valves are used in residential and commercial application for its reliable sealing properties and long service life. The image below is an example of a sectional view of a ball valve.

Components Of a Ball Valve

A ball valve is comprised of the following main components:

1. Valve stem: The valve stem is a rotary shaft connecting the internal ball to the outside lever which when turned rotates the ball.
2. O-ring: The o-ring is used to create a seal between the stem and housing of the valve. NBR (Nitrile rubber) is the most commonly used material for the O-ring.
3. Valve housing: The valve housing protects the internal components and has connection points on the inlet/outlets. Brass, stainless steel and PVC are the most commonly used housing materials. The valve housing may be assembled in one-piece, two-piece or three-piece designs.
   • One-piece: This is the most inexpensive valve option. In the one-piece design, two parts that enclose the ball are connected by pressing and welding, so they cannot be opened for maintenance. Thus, they are used in less demanding applications.
   • Two-piece: The parts in two-piece valves have threaded connections. Thus, they can be disassembled for maintenance purpose. But the valve needs to be removed completely from the pipe to separate the parts for servicing and maintenance purpose.
   • Three-piece: The parts in a three-piece valve are generally clamped by a bolt connection. The valve is not required to be removed completely from the pipe for maintenance purpose. This is the most expensive valve design option, but offers the best solution for sanitary applications.
4. Rotary ball: The spherical rotary ball with a bore allows or blocks the passing of the media through the pipe. They are usually made of stainless steel, PVC, chrome plated steel or chrome plated brass. The ball design is categorized as floating or trunnion based on their design and support.
   • Ball design & support:
   • Floating ball design: The valve seats provide support to the ball to accommodate for different temperature applications. This is the most commonly used ball design. 
   • Trunnion ball design: The ball is supported on the bottom and top to reduce load on the valve seats. This design is used in high quality valves to provide reliable sealing in both high and low-pressure applications.
   • Bore design:
   • Reduced bore: The bore size of these valves is smaller than the diameter of the inlet/outlet connections. Thus, there is a friction loss in the system. However, the losses are still small in comparison to other valves. Most ball valves use a reduced bore design.
   • Full bore: The bore size of these valves is the same size as the diameter of the pipe. Thus, there is no extra friction loss and they are also easy to clean. However, due to its larger diameter, the cost is slightly higher and not required for most application, for which standard reduced bore is sufficient.
   • V-shaped bore: The bore in these valves have a V-shaped profile. Thus, a precise flow rate can be achieved by rotating the ball. A linear flow can be achieved by optimizing the profile of the V-shaped bore.
5. Valve seats: They act as the seal between the ball and the housing of the valve. The most commonly used material for seats is Teflon, but other synthetic materials or metals can also be used.

How Does a Ball Valve Work?

As previously mentioned, a ball valve consists of a rotary ball having a bore. The ball is attached with the stem connected to the lever. The valve can be opened and closed by turning the lever in a manually operated valve (it can also be done with an electric or pneumatic actuator). For the flow to pass, the bore should be aligned along the flow of the fluid. To block the flow, the ball can be rotated perpendicular to the flow path.

A ball valve can have 2, 3 or even 4 ports. Most ball valves are 2-way and are manually operated with a lever. In the open position, the lever is in line with the pipe. When in the closed position, the lever is perpendicular to the pipe. There can be a risk of a water hammer in manually operated ball valves due to a fast-flowing media and quickly closing the valve. The 3-way valves have L or T-patterned bore, which can be seen in Figure 3. This pattern helps in achieving different circuit function such as distributing or mixing flows.

A ball valve is very versatile and can be used in a wide range of industrial applications. They can withstand high temperatures and pressures while offering a long service life at a comparatively lower cost than other valves. However, ball valves are not commonly used as control valves due to its less precise flow control. They can be used in applications that do not require precise flow control accuracy.

Actuation Methods

Ball valves can be manually, electrically or pneumatically actuated.  An electric ball valve uses an electric motor, which is used to rotate the ball for opening and closing the valve. Its reducing gear mechanism reduces the opening and closing speed, thus reducing the risk of a water hammer.

A pneumatic ball valve uses a pneumatic actuator, which generates a torque to turn the valve using the pressure of compressed air. Pneumatic actuators are typically used with larger valves for better operation and cost effectiveness. 

Design Considerations

Ball valves are available in a wide variety of design, materials, temperature and pressure requirements. So, careful considerations should be made while selecting a ball valve for your application.

• Port: Determine if the nature of your application requires 2-way or more ports.
• Actuation method: Depending upon the efficiency and remote operation required for the application, a ball valve can be manually, electrically or pneumatically actuated.  
• Bore size: Determine the diameter requirement for your flow. Most common ball valves have a reduced bore design, but a trunnion ball design supports valves with large diameters (>100mm).
• Materials: The material of the valve depends upon the type of media used in the application. Brass can be used with drinking water, gas, oil and air. Stainless steel can be used if the media is of corrosive nature. PVC valve can be used with acids, bases, salts and organic solvents.
• Pressure: Ensure the valve can withstand the maximum pressure required for your application. A high-performance ball valve designed especially for industrial purpose can support the pressure range up to bar.
• Temperature: Ensure that the valve used can withstand the maximum temperature requirement for your application. A specially designed ball valve may support temperature up to 400°C.

Why Use a Ball Valve?

A ball valve is known for its durability, simplicity, and excellent sealing properties. They provide excellent shutoff even after years of service. This makes a ball valve an excellent choice as a shut off valve. They also provide better resistance to contaminated media than other valves. Ball valves are not commonly used as control valves due to its less precise flow control. However, they are cost effective and can be used in applications that do not require precise flow control accuracy.

Applications

Ball valves are commonly used in drinking water and gas applications.

• Water: The ball valves are used in water applications for flow and pressure control. For drinking water application, the valve must be WRAS, KIWA or DVGW approved.

Gas: These ball valves are also used in gaseous application. They are used with natural gases, liquified petroleum gases, manufactured gases and air for industrial and residential purpose.

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