Figure 1. A double eccentric Butterfly Valve π www. valve-world. net Valve World December 2025
In this article, we discuss the required torque to open and close a double eccentric butterfly valve( Figure 1) and the importance of slipstick effects. The area of focus in a double eccentric butterfly valve is on the shaft seal / bearing and the working seal on the obturator( disc seal), as these have the most influence on the valve’ s operating torque and lifetime. Commercial considerations are also important as the required torque ultimately determines the size of operating components such as gearboxes and actuators. The challenge is to increase the lifetime of the valve seal( reducing running costs) and decrease torque, which is ultimately due to friction within the valve itself. In this article, we focus on the obturator( valve disc) sealing.
SEALING
It’ s all about torque – New double eccentric butterfly valve gasket
A new gasket design( patent pending) greatly reduces adhesion resulting from the‘ slip-stick’ effect that occurs when valves are not operated for a significant period.
By Guenter Oexler and Veli Yiğit
Better sealing, less friction
Existing gasket designs for double-eccentric butterfly valves aim to prevent fluid leakage by maintaining tight contact between the valve disc and the gasket. However, when complete sealing is achieved, the width of the contact surface between the gasket and the disc, along with the high frictional force, significantly increases the torque required during opening and closing operations. This forces the use of larger, more powerful actuators and gearboxes to operate the valves, which in turn increases equipment costs and makes assembly, operation, and maintenance more expensive and complex. When thinking about better sealing with less friction, we need to keep in mind the different butterfly valve designs, such as the stainless-steel seat ring used in epoxy-coated valves and the seat-ringless design of enamel-coated butterfly valves( Figure 2). Additionally, because double eccentric butterfly valves flow in both directions- in seat and off seat- the valve must tightly seal in both directions. We have mentioned the commonly used gasket together with a stainless-steel seat ring. It is self-evident that this sealing composition requires very high torque to achieve a tight seal, especially at higher media pressure, due to the large contact area( Figure 3). Additionally, we must consider that these valves typically undergo few ON-OFF-ON cycles over their lifetimes. Here, we encounter the so-called slip-stick effect, which occurs when butterfly valves remain in the closed position for extended periods, leading to adhesion between the sealing gasket and the gasket seating surface. This adhesion effect can become severe, significantly increasing the torque required during opening and closing operations, particularly if valves are not operated for long periods. This makes it
About the authors Guenter Oxler is a Process Engineer with decades of experience. He has been a process industry consultant for more than twenty years.
Veli Yiğit is the Head of Engineering at SAMSUN Makina Sanayi in Ankara, Türkiye.
Figure 1. A double eccentric Butterfly Valve π www. valve-world. net Valve World December 2025
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