Flanged double offset butterfly valve

Flanged double offset butterfly valve has a two-offset disk which can be used up to 1,480 psi [10 MPa]. Compared to the single-eccentric design, the double offset butterfly valve uses a stem which is present behind the disk. In the high-performance butterfly valve, the second offset stem is pushed back to one side from the middle of the disk. This offset geometry allows the disk to be rubbed over the seat with just 1° to 3° of 90° rotation.

The action of the flanged double offset butterfly valve refers to the cone profile while sealing the valve. The configuration of the disk and shaft offsets produces the cam action of the disk in the seat, minimizing the torque required to operate the valve.

Double offset butterfly valve classification

Based on the connection there are four main types of high performance or double offset butterfly valve.
Wafer Type: The wafer type of the double offset butterfly valve is constructed to provide a strong sealing, safeguard against bi-directional pressure differentials, and to prevent any backflow in devices that were built for unidirectional flow. This is done by the use of a tightly fitted seal material, such as an O-ring, gasket, precisely machined, along with a smooth valve face on the downstream and upstream parts of the valve.

Lug Type: In the lug body type of the double offset butterfly valve configuration one end of the pipeline can be removed without impacting the other side of the valve. This can be achieved with threaded inserts, flanges, and two sets of lugs (bolts) that do not use nuts so each flange has its bolts. In a Lug type connection, you do not have to shut down the whole device to inspect, clean, repair, or replace the lug butterfly valve.

Flanged End Type: The flanged end type double offset butterfly valve uses a flange at both ends of the valve to be attached with pipe flanges. This type of end connection is used for the very large size of the butterfly valve.

Welded End Type: The welded end type double offset butterfly valve is used where the system is under very high pressure. These types are generally used for small size butterfly valves.