A common question with new users of the belleville washer is “How much torque do I need to apply during installation?” and the definitive answer is…it depends.  Several factors will play a large part in how much torque is required, such as gasket load requirements, bolt condition, coatings or lubrication on the bolt, and user preference.  Ultimately though, the answer comes from the sealing load needed on the gasket, not from the belleville washer.

To better understand this, we need to understand torque and its relationship to a bolted system.  Torque is a rotational force which, when applied to a bolt, is converted to an axial load, stretching the bolt like a spring.  As additional torque is applied to the nut, the bolt continues to stretch.  Meanwhile, this spring-like stretch of the bolt pulls the flanges together and applies a clamping force on the gasket.  It is this clamping force, or “gasket load”, that prevents leaks and emissions at the flanged connection.

So how does a belleville washer affect the above scenario?  As a type of spring, the belleville acts similar to the bolt and stretches while the nut is being torqued.  However, the belleville will not affect the torque required to provide proper clamping load on the gasket.  Instead, the belleville only increases the available stretch in the system, which will require more turns of the torque wrench to reach to correct torque value.

For a thorough analysis of determining bolt torque, we highly recommend an excellent article written by the Fluid Sealing Association for their monthly Sealing Sense column published by Pumps & Systems Magazine, which can be found here:  “How do I determine bolt torque for flanged connections?”

In summary, each gasket and flanged connection has its own unique properties, and therefore it is best to consult with the supplier of the gasket for their recommended torque value.  The belleville washer can then be added seamlessly and no modification to this torque value is needed.

Should you have any additional questions, our engineering team here at Belleville International is available for your convenience and can be reached by calling 877-235-5384.

References:

Fluid Sealing Association (2008, June). How Do I Determine Bolt Torque for Flanged Connections. Pumps & Systems Magazine

          Retrieved from http://www.pumpsandsystems.com/topics/seals/how-do-i-determine-bolt-torque-flanged-connections