Concentric Vs. Eccentric Reducer

Pipe reducers are a vital type of fitting used to regulate flow in piping systems. There are two primary types: concentric reducers and eccentric reducers. This discussion will cover both types, their functions, and scenarios for their use. While reducing or expanding pipe sizes is typically straightforward, certain exceptions must be considered to maintain the system's integrity.  

What is a Pipe Reducer?  

In simple terms, a pipe reducer is a fitting that transitions a larger pipe to a smaller one, thereby reducing the pipe size within the system. Pipe reducers are often used to connect pipes of varying sizes, accommodating diverse flow requirements. Depending on the application, the materials flowing through the pipes, and system specifications, different types of reducers may be needed.  

Selecting the right pipe reducer can be complex, as the fit and material compatibility are critical factors. However, once the appropriate reducer is identified, the installation process is typically quick and straightforward.

When to Use a Pipe Reducer  

Pipe reducers are commonly used to adapt pipes of different sizes, but their applications can extend to more complex scenarios. For instance, they may be required when the flow in a piping system needs to be restricted or expanded, particularly if dictated by the hydraulic requirements of the system. However, using a pipe reducer impacts the entire system, as it alters both flow and pressure, making careful consideration essential.  

Once the need for a pipe reducer is established, the choice between a concentric and an eccentric reducer must be made. While concentric reducers are the more commonly used option, there are specific situations where an eccentric reducer may be the better choice.

Concentric vs Eccentric Reducer: What's the Difference?

While this may seem complicated, it's actually quite simple. Concentric reducers reduce the pipe in the center. So, if you’re looking at the reducer head-on, you can see the smaller section is formed in the direct center of the larger side. Eccentric reducers reduce the pipe to the side. When viewed head-on, an eccentric reducer shows the smaller section offset to one side of the larger section. While this may seem like a minor difference, it has significant implications for flow.  

A cone-shaped concentric reducer aligns the centerlines of the pipes, while an eccentric reducer misaligns them. This distinction affects fluid dynamics. Most reducers are concentric, but eccentric reducers are necessary when pipes must maintain the same top or bottom level. They are often used to prevent air entrapment, making them suitable for systems where air and liquids flow together.  

In general, concentric reducers are more commonly required, as most applications do not demand a flat side on the reducer. However, eccentric reducers can be effective when properly installed, ensuring the flat side aligns as needed. Improper alignment can lead to liquid or gas accumulation. Notably, when reducers are used vertically, there is little difference between concentric and eccentric designs.

Concentric and Eccentric Expanders  

Reducers also function as expanders when used in reverse. Both concentric and eccentric designs serve this dual purpose, and their effects on flow dynamics remain the same regardless of the direction of use. Whether reducing or expanding, their role is to transition between pipes of different sizes.  

Installing Reducers  

The installation method depends on the materials of the reducer and the pipes. Metal reducers are typically butt-welded, while PVC reducers are often glued or fitted. Some reducers offer push-to-fit or crimp installation options, depending on their design and application.  

To install a reducer, it is fitted to both pipes and secured according to the material and connection type. For eccentric reducers, alignment is critical:  

- In horizontal liquid piping, the flat side must face up to prevent gas collection.  

- In horizontal vapor piping, the flat side should face down to avoid liquid accumulation.  

The extent of the size reduction affects flow. A slight reduction generally causes minimal impact, whereas a significant reduction requires careful consideration to maintain system performance.

Finding the Right Pipe Reducer  

Knowing whether you need a concentric or eccentric pipe reducer is just the starting point. You must also consider the material of the pipes being connected—options include metal, PVC, PEX, and more—each requiring a specific connection method. For metal pipes, a welded reducer might be suitable, while PVC pipes may need reducers that can be glued or fitted.  

Exact sizing is crucial. Pipe fittings are sized based on the outside diameter for male pipes and the inside diameter for female pipes. This means you need to identify your pipe type, exact size, and material. The simplest way to ensure a proper fit is to bring the pipes with you to compare them directly to the available fittings.