Double offset butterfly valves are commonly regarded as high-performance butterfly valves. They are among the most popular eccentric butterfly valves in the market, apart from triple-offset valves. Additionally, they have often considered the finest type of butterfly valves.
DOUBLE OFFSET BUTTERFLY VALVE
Industrial valves require a broader pressure and temperature range than traditional butterfly valves could achieve. This has led to the development of a high-performance butterfly valve. Double eccentric butterfly valves provide a simple, lightweight, compact and cost-effective structure with a low operating torque benefit.
What is Double Offset Butterfly valve?
High-Performance Butterfly Valves uses a disk offset from the centre of its seat, due to which it is named as Double Offset butterfly valve. In this setting, the disk is eccentric or offset from the seat of the valve. When the disk begins to rotate, it shifts away from the seat instead of around it. In fact, this design utilizes line pressure to help give it a proper sealing. This functionality allows the usage of double offset butterfly valves in high-pressure systems such as ethanol or HVAC. PTFE or plastic are used commonly as a seat material in double offset valves, but metal seats are also provided to meet fire-testing requirements such as API 607.
Classification By Connection Type
Based on the connection there are four main types of high performance or double offset butterfly valves.
- Wafer type ends.
- Lug type ends.
- Both flanged ends.
- Butt-welded types end.
Wafer Type: The wafer type of the double offset butterfly valves 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 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 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 butterfly valve is used where the system is under very high pressure. These types are generally used for small size butterfly valves.
How does Double Offset Butterfly Valve Work?
Double-offset butterfly valves have a two-offset disk which can be used up to 1,480 psi [10 MPa]. Compared to the single-offset 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 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.
When to use Double offset butterfly valve?
The double-offset butterfly valve is designed to be used in applications requiring greater resistance to the pressure. The disk is placed in the center of the pipe bore and designed to improve the sealing capability and minimize valve wear.
High-performance butterfly valves are suitable for application in water, wastewater, oil, steam and gasses in a cost-effective, compact build. Their corrosion-resistant, single-element thrust bearing and disk spacer eliminates body wear and helps maintain a positive centering of the disk in the valve bore.
Double-offset butterfly valves can be operated manually using a handle, or with gears or actuators. These devices rotate the valve disk to the ideal location for effective sealing or complete opening of the valve. High-performance butterfly valves are used mostly in the water, chemical and petrochemical industries and can also be used in fuel handling & control and many other applications.
Difference Between Double and Triple offset butterfly Valve
- The double offset butterfly valve has two offsets at the center that produce cam action at the time of the application process.
Triple offset butterfly valves (TOV) have three different offset valves. Two offsets are located at the centre whereas the third is on the seat surface which creates the shape of the disk and seat form of the cone.
- The double offset Butterfly valve can be used for an application of up to 325°C and can be used in pressure as high as 50 bars. While a Triple Offset Butterfly valves can be used for a demanding & long-term application of up to 932°F (500°C) and the valve is designed to withstand a high pressure of up to 725 psi (50 bar).
- Double offset butterfly valve seat is made up of soft material while in triple offset butterfly valve seat is made of hard metal.
- One of the key distinctions between the two butterfly valves is their appearance. In the double offset butterfly valve, the two offsets of this type of valve allow easy opening and retain their strong sealing strength.
NTGD Valve is a experienced double offset butterfly valve manufacturer, please feel free to send us mail if you have any inquiry.