Butterfly Valves
Optimising bolt tightening torque for reliable rubber sealing in butterfly valves
Butterfly valves are widely used in water systems and industrial pipelines, where maintaining a tight seal is essential for preventing leaks and ensuring reliable operation.
This technical article investigates how bolt tightening torque affects the sealing performance of rubber seals in butterfly valves.
By Ahmed Obaid, Sierra
Butterfly valves are commonly used in water networks, process plants and industrial systems due to their simple design and efficient flow control. One of the key components in ensuring proper sealing is the rubber seal on the valve disc, which forms a seal by compressing around the valve disc when closed. However, the amount of tightening torque applied to compress the rubber seal plays a critical role in performance. If the torque is too low, the rubber does not compress enough, leading to leakage. If the torque is too high, the rubber gets over-compressed, which causes early deformation, loss of elasticity, higher valve operating torque and reduced lifetime. This article outlines a mathematical approach used to estimate the optimal tightening torque to ensure sealing without compromising the integrity of the rubber seat. A practical test is also discussed to validate the method. The following figures illustrate the effect of bolt tightening torque on the compression of the rubber seal. As shown in Figure 2, excessive or uncontrolled torque can deform the seal due to elevated contact stress. This leads to greater radial expansion of the rubber, which in turn increases the pressure stress caused by contact with the valve seat. Consequently, the friction force acting on the seal during opening and closing is increased, raising the likelihood of accelerated wear.
Minimum required rubber seal diametral expansion
To achieve an effective seal, the rubber seat must expand slightly outward( radially) when compressed by the disc. This expansion generates a contact pressure that pushes against the disc surface, strong enough to resist the internal pressure of the fluid flowing through the pipeline.
The required amount of expansion depends on:
• The amount of tightening torque of retainer bolts which compress the seal rubber
• Number of retainer bolts
• Retainer bolt size
• Contact area between retainer and rubber seal
• The stiffness( hardness) of the rubber material
• Rubber seal thickness This radial expansion must be carefully estimated to provide enough sealing pressure, while also including a safety margin to account for manufacturing tolerances, aging and thermal effects.
Figure 1: Seal shape with calculated bolts tightening torque.
Figure 2: Seal shape with uncalculated bolts tightening torque.
44 Valve World May 2025 www. valve-world. net