Concentric and Eccentric Reducer Fittings

Reducers are among the most widely used fittings in the piping industry, and they work exactly as their name suggests. Available as concentric and eccentric reducer fittings, a reducer reduces the flow of water or fluid. Reducing here does not mean controlling the flow like a valve, which opens or closes

to make the flow smaller or larger; only the pipe size is reduced. A reducer therefore joins a larger diameter to a smaller one, or vice versa.

Basically, reducers come in two styles: the concentric reducer and the eccentric reducer. The eccentric reducer is the one most widely used in the piping industry.

Reducer fittings are divided into two types:

1. Concentric Reducer

A concentric reducer is a type of reducer fitting with a single center point or centerline, which gives it better balance than an eccentric reducer.

Concentric & Eccentric Reducer Fittings

A concentric reducer is also called a welded concentric coupling. It allows a large pipe to be connected to a smaller pipe by welding. A concentric reducer allows a welded joint between pipes that share the same centerline.

Concentric reducers are more commonly used on vertical lines or pipes, especially when the pump is a top-top type (both suction and discharge face upward). This type of pipe joint can also be used for various bore sizes, and once connected there is no chance of air becoming trapped inside.

2. Eccentric Reducer

The eccentric reducer is the type more commonly used, especially on components located close to a pump. This is to avoid the possibility of air becoming trapped inside.

Concentric & Eccentric Reducer Fittings

Eccentric reducers are divided into two types:

a. Bottom Flat Reducer

This reducer has a straight side at the bottom. Bottom flat reducers are commonly found on pipe racks, so that condensate can flow fully to the lowest point below the pipe. As the name suggests, the bottom flat reducer has a straight bottom side, and it is also usually used on pipes that carry steam or gas vapor. This is because pipes carrying gas contain liquid from condensation (condensate). To help the condensate flow downward, a bottom flat reducer is used so that the condensate runs to the lowest part and collects in the steam trap.

b. Top Flat Reducer

This type of reducer is used when the pump suction comes from below, or when the suction comes from a horizontal pipe. If a bottom flat or concentric reducer is forced into this suction configuration, the concern is bubbles, or air trapped along the top side.

Paying attention to trapped air is important because it makes suction ineffective, so space that should be filled with water is filled with air instead.

Concentric & Eccentric Reducer Fittings

Figure 3. Flat on top and flat on bottom

Installing Eccentric and Concentric Reducers

There are various ways to install eccentric and concentric reducers, including:

1. Duct sealant

2. Self-drilling screws

3. Duct tape

4. Hose clamps

5. Welding

6. Threaded connection

When using flexible ducting, the common method for securing the joint is a hose clamp, better known as a Jubilee clip. This accessory gives a strong grip when tightened properly.

If you use welding, however, make sure to clean oil and other contaminants from the surface to get a strong weld. It is best to clean all pollutants and dirt from the reducer and pipe with alcohol.