Double eccentric butterfly valves are generally considered high-performance butterfly valves. Together with triple offset valves, they are one of the most popular eccentric butterfly valves on the market. Additionally, they are often considered the best type of butterfly valve.
DOUBLE OFFSET ISOLATION VALVE
Industrial valves require a wider pressure and temperature range than traditional butterfly valves. This led to the development of a high-performance butterfly valve. Double eccentric butterfly valves offer a simple, light, compact and economical structure with the advantage of low operating torque.
What is a double displacement globe valve?
Heavy-duty butterfly valves use a disc offset from the center of their seat, which is why they are called a double-offset butterfly valve. In this configuration the disc is eccentric or displaced from the valve seat. As the disc begins to rotate, it moves away from the seat rather than around it. In fact, this design utilizes line pressure to ensure a proper seal. This functionality allows the use of double displacement butterfly valves in high pressure systems such as ethanol or HVAC. PTFE or plastic is often used as the seat material in double offset valves, but metal seats are also supplied to meet fire safety requirements such as API 607.
Classification by connection type
Based on the connection, there are four main types of heavy duty or double offset butterfly valves.
- Wafer type ends.
- Ends with eyelets.
- Both end with a flange.
- End of butt welded types.
Type of wafer:
Wafer-type double offset butterfly valves are designed to provide a strong seal, protect against bidirectional pressure differentials, and prevent any backflow in devices built for unidirectional flow. This is achieved by using a tightly fitted sealing material such as: B. an O-ring, a precisely machined seal and a smooth valve surface on the downstream and upstream parts of the valve.
Eyelet Type:
The butterfly valve grommet body configuration allows one end of the tubing to be removed without affecting the other side of the valve. This can be achieved with threaded inserts, flanges and two sets of handles (screws) that do not use nuts, so that each flange has its own screws. With a grommet connection, you do not need to turn off the entire unit to inspect, clean, repair or replace the grommet butterfly valve.
Flange End Type:
The flanged butterfly valve uses a flange at both ends of the valve, which is connected to the pipe flanges. This type of end connection is used for very large butterfly valves.
Welded End Type:
The welded ends shut-off valve is used where the system is under very high pressure. These types are generally used for small size shut-off valves.
How does a dual offset shutoff valve work?
Double offset butterfly valves have a double offset disc that can be used up to 10 MPa (1,480 psi). Compared to the single-offset design, the double-offset butterfly valve utilizes a spindle located behind the disc. In the heavy-duty butterfly valve, the second travel spindle is pushed back from the center of the disc to one side. This offset geometry allows the disc to rub against the seat with just 1° to 3° of 90° rotation.
The effect of the double displacement globe valve refers to the cone profile in the valve seal. The disc and shaft offset configuration creates cam action of the disc on the seat, minimizing the torque required to operate the valve.
When should a double offset shutoff valve be used?
The double displacement globe valve was designed for applications that require greater pressure resistance. The washer is located in the center of the tube bore and is designed to improve sealing ability and minimize valve wear.
High-performance butterfly valves are suitable for use in water, wastewater, oil, steam and gases and are characterized by a compact and economical design. Its corrosion-resistant, one-piece thrust bearing and disc spacer prevent casing wear and ensure secure centering of the disc in the valve bore.
Double offset butterfly valves can be operated manually with a lever or with gears or drives. These devices rotate the valve disc to the ideal position for effective sealing or full opening of the valve. Heavy duty butterfly valves are primarily used in the water, chemical and petrochemical industries and can also be used in fuel handling and control and many other applications.
Difference Between Double and Triple Offset Butterfly Valves
- The dual offset shutoff valve has two offset valves in the middle that create a cam effect during the application process.
Triple offset butterfly valves (TOV) have three different valve displacements. Two offsets are in the center while the third is on the seat surface, which creates the disc shape and the cone seat shape.
- The double displacement shut-off valve can be used for applications up to 325°C and at pressures up to 50 bar. Triple displacement globe valves can be used for demanding, long-term applications up to 932°F (500°C) and the valve is designed to withstand high pressure up to 725 psi (50 bar).
- The double offset butterfly valve seat is made of soft material, while the triple offset butterfly valve seat is made of hard metal.
- One of the main differences between the two butterfly valves is their appearance. For the double offset butterfly valve, the two offsets of this type of valve allow it to open easily and maintain its strong sealing force.
