What are the Differences between Zero Offset, Double Offset and Triple Offset Butterfly Valves?
Choosing the wrong type of valve may adversely affect your operation. There are several different types of butterfly valves on the market, including zero offset, double offset and triple offset. Valve engineers from ZECO Valve Group Co., Ltd. help you distinguish and understand them.
Also known as concentric design, this is common in general service "elastic seat" or "rubber seat" butterfly valves. The stem and disc are located in the center of the seat, and all seats are located in the body of the valve. The disc keeps constant contact with the seat. One advantage of this valve is that it does not touch the valve body through the medium of the valve, because the seat is constructed as a body or spool inside the valve body. Zero eccentric butterfly valves are suitable for basic and special liquid and gas applications up to 200 PSI and up to 400 degrees Fahrenheit. Zero eccentricity butterfly valves can handle chemical, paint, food, some solid and abrasive applications. Zero eccentric butterfly valves are made of epoxy coated cast iron and stainless steel. There are many seat materials, such as butadiene rubber, ethylene propylene Diene rubber, Vitron, Teflon, natural rubber, etc.
Double eccentric butterfly valve
This popular valve is also known as a high performance butterfly valve. The valve has two off-center stem. This creates a cam operation during the application process.
1ST offset: The axis of the shaft is behind the central line of the sealing point of the disc seat.
2ST offset: The axis of the shaft is eccentric to the center of the valve/pipeline.
Double offset butterfly valves are usually used for:
Power generation, pulp and paper making, HVAC, chemistry, oil and gas, water and wastewater treatment, shipbuilding
The pressure of double offset butterfly valve is higher than that of zero offset butterfly valve. Dual bias in carbon steel, stainless steel, Hastelloy and other body materials to achieve ANSI Class 600, with Teflon seat changes and metal support seat fire safety design.
Triple offset butterfly valves have three offsets. Two are placed in a position similar to the double offset butterfly valve, while the third offset is the geometric shape of the seat surface, forming the conical shape of the disk and seat. The taper angle and the offset of two eccentric axes allow the disc to seal the seat without friction.
This seating design also allows for uniform sealing to achieve tight closure of metal seating design. Compared with other types of metal seat valves, this design is a lower cost, lower torque option (easier to automate). Triple offsets are commonly used in gate-like applications where metal seats are required, and close closures and/or quarter-turn actuation are required. High pressure steam (over 150 PSI), superheated steam, high temperature gas and oil, high temperature applications, etc. are beneficial for this type of valve because metal seats are required on soft seats. Triple offset butterfly valves are used in similar industries such as double-offset butterfly valves, but the requirements are higher.
If you have any other questions, please feel free to contact ZECO Valve Group Co., Ltd. The Valve Team of ZECO Valve Group Co., Ltd. has many years of experience and is willing to help you!