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What is a Double Eccentric Butterfly Valve?

If you’re in the water industry, you may not have heard about double eccentric butterfly valves, or a double offset, they are the same thing. So what exactly are they, and how do they work?

In this blog, we’ll delve into the ins and outs of double eccentric butterfly valves and explore the vast advantages that they offer.

Av-Tek Valves use only the highest quality materials. We are committed to providing our clients with the best products and services to create quality solutions for projects and people. To learn more, you may call us at (385) 325-2504 or (801) 637-8541 or leave us a message here.

Double Eccentric Butterfly Valve: Basic Overview

A double offset butterfly valve, we call it our DEX valve, is a high-performance butterfly valve designed to resolve many of the common complaints about standard/concentric butterfly valves.

It’s called “double eccentric” because the valve body seat is offset to the front side of the body, and the disc is offset to the front side of the shaft.

Most Common Complaints

Here are some of the most common complaints about AWWA standard C504 butterfly valves:

1. They leak

Many butterfly valves leak because when they are in the open position, the disc pinches the rubber seat causing a seatset or leak path. This creates a visible divot in the rubber seat, which allows water to leak by when they are closed.

2. They seize or won’t close

The inside of the body shaft area of most butterfly valves are not coated. They are raw iron in this area. If they were coated, the coating would wear as the valve is opened and closed causing the disc to flutter, and destroying the valve.

Many butterfly valve manufacturers use plastic sleeves or packing glands to wrap the shafts, which allow water into the uncoated area of the shaft body.

3. Raw iron + Water = Corrosion

To resolve this problem, many manufacturers require an exercise program to break up the rust caused by a faulty design.

Benefits of Using DEX Valves

Double eccentric butterfly valves offer several benefits, including:

1. Leak-free Design

Because the double eccentric butterfly valve features a double offset design, the disc and seat do not touch when the valve is in the open position. This eliminates the risk of creating a seatset, or leak path, which is the number one complaint with butterfly valves.

2. Exercise Program NOT Required

Properly designed and manufactured double eccentric butterfly valves, utilize bronze bushings and O-ring seals to prevent water from entering the valve shaft area. This design eliminates the corrosion caused by plastic sleeves and packing glands. Since there is no need to break up corrosion and rust caused by a poor design, you can leave the valves in the open position until you need to close them.

3. Versatility

Double eccentric butterfly valves are known for their versatility. They are an excellent choice when critical service valves are needed. In other words, if you need a valve that will isolate the media and not leak these are the valves for the application. They can be used for pump control, air valve isolation, reservoir intake isolation, transmission lines, PRV isolation, and general isolation around the plant or in the distribution system. They are designed for use in clean water, industrial, and gas applications.

4. Low maintenance

Double eccentric butterfly valves are known for their low maintenance requirements. These valves are designed to last and are easy to repair if needed, reducing the overall cost of ownership.

Av-Tek’s DEX Double Eccentric Butterfly Valves

It’s important to choose a valve capable of handling tricky applications and meets all the requirements for your project. If you’re looking for a reliable and effective valve, consider the DEX Double Eccentric Butterfly Valves.

The following are its top four features:

1. Leak-Free Guarantee

DEX Double Eccentric Butterfly Valves are designed to be leak-free. They even come with a unique warranty that offers a leak-free guarantee for a minimum of three years. *Guarantees up to ten years are available depending on the application and requirements of the project.

2. Corrosion-resistant

Unlike standard butterfly valves that use plastic sleeves or packing glands creating a wetted shaft in an uncoated area, the DEX Double Eccentric Butterfly Valves have a dry shaft with eight

O-ring seals. This prevents corrosion and ensures that the valve does not need to be exercised regularly, as is required for standard butterfly valves.

3. Easy to Maintain

At Av-Tek, our DEX Double Eccentric Butterfly Valves are easy to maintain in all sizes from 6” to 120”. The first scheduled maintenance is at 20-25 years, and repair kits are reasonably priced and simple to install.

4. Availability

Av-Tek strives to always have industry leading lead times. We know the demands of the industry and do our best to help you avoid downtime. The smaller sizes, from 6” to 42”, are almost always In-Stock and ready to ship. Larger sizes, and large projects, are available quickly to help keep even the most complex projects moving forward without delays.


When choosing a valve for your system, it’s essential to consider your system’s specific needs. Selecting the right valve can help reduce disruptions and maintain smooth operations for your system.

Moreover, you can count on DEX Double Eccentric Butterfly Valves as a reliable choice for your various applications. They help to maintain optimal operations while maximizing long-term cost savings.

Reach out to us for all your questions regarding DEX Double Eccentric Butterfly Valves. You may call us at (385) 325-2504 or (801) 637-8541 or leave us a message here to learn more.

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