Whiffletree System for Sealing Flanged Connections

Technology Summary

The sealing of flanges is usually accomplished with a clamping force provided by multiple individual fasteners. In order to get a good seal, the individual fasteners must be tightened uniformly. This can be a sensitive and time-consuming process requiring high levels of workmanship, particularly for Ultra-High-Vacuum (UHV) and large flanges. When multiple fasteners are used in close proximity, tightening of one fastener can reduce the preload on adjacent fasteners, compromising the ability to know the preload at the joint. So in certain niche applications where load, uniformity, or time-in-work constraints are of great importance, traditional flanged connections can present some disadvantages. 

The Invention

Fermilab has developed a way to seal flanges by applying the clamping force through a “Whiffletree” structure that ensures load uniformity around the sealing surface. The system can be sealed by tightening a single fastener, which reduces the time required to make the connection and improves the ability to know the preload in the fastener and the sealing load. Uniformity of sealing force is determined by the designed configuration of the whiffletree rather than by workmanship.   


The benefits offered by a whiffletree flange sealing structure are:

  • Improved uniformity of sealing load around a sealing surface
  • Ability to tailor sealing load to unique geometry (e.g. to provide higher forces at the corners of rectangular flanges)
  • Improved ability to determine actual joint preload
  • Reduced personnel time to make up a connection
  • Improved reliability and reduced rework

Applications and Industries

Applications for this technology include

  • Uniformity-critical seals (e.g. indium or brittle substrates, UHV seals)
  • Load-critical seals
  • Time-critical seals (e.g. high-radiation environments with limited personnel access)
  • Tailored sealing force profiles for non-circular geometries
  • Low-particulate applications (e.g. superconducting systems)


Category: Engineering Technologies, Environmental & Safety

Tags and Keywords: Whiffletree, Flange, Vacuum


Whiffletree prototype

Invention Details

Patent Status: Patent Pending

Aaron G Sauers, CLP
Fermilab, MS 312 – PO Box 500
Batavia, IL 60510