A Complete Guide to Double Offset Butterfly Valve Installation

Posted by Aira Euro on December 16th, 2022

A double offset butterfly valve is commonly regarded as a high-performance butterfly valve. Apart from triple-offset valves, they are among the most popular eccentric butterfly valves. Furthermore, they have often been considered the finest type of butterfly valves.

The pressure and temperature ranges required by industrial valves are greater than what can be achieved by traditional butterfly valves. The result was the development of a high-performance butterfly valve. Featuring a simple, lightweight, compact, cost-effective structure with low operating torque, double eccentric butterfly valves are simple, lightweight, compact, and cost-effective.

What is a Double Offset Butterfly valve?

A high-performance butterfly valve has a disk offset from the center of its seat, hence the name Double Offset butterfly valve. In this setting, the disk is eccentric or offset from the valve seat. When the disk rotates, it shifts away from the seat instead of around it. This design relies on line pressure to provide proper sealing. Due to this functionality, double offset butterfly valves can be used in high-pressure systems such as ethanol or HVAC. In double offset valves, PTFE or plastic is commonly used as a seat material, but metal seats are also available for fire-testing requirements such as API 607.

Classification By Connection Type

There are four main types of high performance or double offset butterfly valves based on the connection.

• Wafer type ends.

• Lug type ends.

• Both flanged ends.

• Butt-welded types end.

Wafer Type: Designed for unidirectional flow, the wafer type of double offset butterfly valve provides a strong seal, prevents bi-directional pressure differentials, and prevents any backflow. In order to achieve this, a tightly fitted seal material, such as an O-ring, a gasket, and a smooth valve face is used on the downstream and upstream sides of the valve.

Lug Type: The lug body type of the butterfly valve configuration allows one end of the pipeline to be removed without affecting the other side. This can be accomplished by using threaded inserts, flanges, and two sets of lugs (bolts) that do not use nuts, so each flange has its own bolts. If you want to inspect, clean, repair, or replace the lug butterfly valve, you don't have to shut down the whole device.

Flanged End Type: Butterfly valves with flanged ends are attached with pipe flanges at both ends of the valve. For very large butterfly valves, this type of end connection is used.

Welded End Type: The welded end type butterfly valve is used when the system is under very high pressure. In general, these types of butterfly valves are used for smaller sizes.

How does Double Offset Butterfly Valve Work?

A double-offset butterfly valve has a two-offset disk capable of handling 1,480 psi [10 MPa]. Unlike the single-offset design, the double-offset butterfly valve uses a stem behind the disk. The second offset stem is pushed to one side from the middle of the disk in the high-performance butterfly valve. The offset geometry allows the disk to be rubbed over the seat with just 1° to 3° of rotation at 90°.

As the valve seals, the cone profile of the double offset butterfly valve is in action. Due to the disk and shaft offsets, the disk acts like a cam in the seat, minimizing the torque required to operate the valve.

When to use Double offset butterfly valve?

It is designed for applications requiring greater pressure resistance. Disks are placed in the center of pipe bores to improve sealing capabilities and minimize valve wear.

With a compact, cost-effective design, high-performance butterfly valves are suitable for water, wastewater, oil, steam, and gasses. A corrosion-resistant, single-element thrust bearing and disk spacer help maintain a positive centering of the disk in the bore of the valve.

The double-offset butterfly valve can be operated manually or with gears or actuators. Using these devices, the valve disk is rotated to the ideal location for sealing or completely opening the valve. Among the applications of high-performance butterfly valves are water, chemical, and petrochemical industries, as well as fuel handling and control.

Difference Between Double and Triple offset butterfly Valve

• As a result of its offsets at the center, the double offset butterfly valve produces cam action when applied.

• There are three different offset valves on triple offset butterfly valves (TOV). There are two offsets at the center, and one on the seat surface, which determine the shape of the disk and seat of the cone.

• A double offset Butterfly valve can withstand temperatures up to 325°C and pressures up to 50 bars. A Triple Offset Butterfly valve can be used for demanding & long-term applications up to 932°F (500°C) and is designed to withstand pressures of up to 725 psi (50 bar).

• Soft material is used for double offset butterfly valve seats, while hard metal is used for triple offset butterfly valve seats.

• Their appearance is a key difference between the two butterfly valves. Double offset butterfly valves have two offsets that allow for easy opening and maintain strong sealing.