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Determining the Residual Seal Force (RSF) on Medical Vials

Indirect residual seal force on medical vials

Residual seal force (RSF) is the force with which the rubber stopper between the flanged cap and the neck of the vial is braced. This force measurement provides an indirect indication of the current integrity of the vial closure. However, these measurements must be correlated with established leakage tests.

There are two diverse tests for determining the integrity of primary packaging (container-closure integrity tests) (from PDA technical report number 27, pharmaceutical package integrity (2)):

  • Microbial immersion test
  • Microbial aerosol challenge
  • Bubble test
  • Liquid tracer test
  • Dye leak test
  • Helium leak detection
  • High voltage leak detection
  • Corona discharge test
  • Pressure/vacuum decay
  • Vacuum retention
  • Headspace gas analysis

The following methods should be prioritized

The following methods should be prioritized over the highly popular dye test:

  • Vacuum decay
  • High voltage leak detection
  • Laser-based headspace detection

a) The safety cap must be removed from the closure before testing
b) The flanged cap holds the stopper under pre-load
c) When a suitable compression load is applied to the rim of the flanged cap, it lifts from the neck of the via. This is displayed as the reduction in force in the force travel diagram. The inflection point indicates the RSF value.


  • USP <1207> This chapter contains guidance for integrity assurance of non-porous packaging intended for sterile pharmaceutical products.

ZwickRoell test fixture for determining the residual seal force

For testing the residual seal force of flanged caps, ZwickRoell recommends a device with inserts and compression dies of various sizes. The preload force of the rubber stopper on an aluminum flanged cap indicates the seal integrity of the vial closure.

  • The test kit consists of a lower mounting platform for supporting the vial. An integrated prism centering aid with scale is used to read the vial diameter (6 mm to 70 mm) and
  • The fixture is available with inserts and compression dies of various diameters (8.0 mm, 13.8 mm, 20.7 mm, 28.5 mm, 32.94 mm). For the respective test, the die diameter should correspond with the protective cap diameter.
  • A modular design allows the various inserts to be changed quickly and easily.
  • an upper compression test kit with locking nut for pre-positioning the die holds the compression die.
  • Load is applied via a ball joint to compensate for deviations from parallel up to approximately 1°. All of the components are made of rust-free high-grade steel.
  • It can only be used in conjunction with a safety device.

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