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What is an Eccentric Reducer?

M. McGee
M. McGee

An eccentric reducer is a part of a pump system that is placed directly in front of the impeller. The purpose of the eccentric reducer is to properly mix substances that have different densities to reduce variations in the pump system. If the pump didn’t contain one of these parts, high-density material would sit at the bottom of the intake and low-density would sit at the top. The substances would move into the system as separate materials, causing vibrations and potentially damaging the pump system.

In a majority of cases, the eccentric reducer handles air-water mixture or an oil-water mixture. In both cases, the substances don’t like to mix and will separate in the pipe if given time to do so. If they hit the pipe as two separate substances, the impeller would move easily through the low-density zone and hit the high-density with too much force. This could seriously damage the motor running the pump.


Most of these parts operate on a purely mechanical level; they don’t have any moving parts. An eccentric reducer looks like a tube with two differently-sized openings. Generally, one side of the tube is directly perpendicular to the openings, and the other side is angled. These devices are usually installed so that the fluid moves horizontally through the two holes, from the large hole to the small hole.

The part operates by increasing the pressure inside the pipe. When a liquid flows through a pipe, it tries to maintain speed and pressure. Should the pipe widen, the flow slows down as a result of the drop in overall pressure; if the pipe narrows, it will speed up from the pressure increase. An eccentric reducer narrows the flow, which results in increased pressure and speed.

Depending on the material being pumped, the eccentric reducer is placed with the angled side going up to the pump or down to the pump. If the secondary material in the flow is less dense than the main material, the angle side goes down into the pump. When the secondary material is more dense, it angles up. In either case, the angle forces the two materials to remix before entering the pump.

When the material hits the sloped eccentric reducer, it tries to continue to flow. If the reducer angles down into the pipe, the low-density material will be forced down into the main flow; if the reducer angles up, the material is forced up into the main flow. The increased speed of the main flow will pull the different-density material along with it quickly enough that it won’t have time to separate until after it is past the pump.

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