Versaperm Vapour Permeability measurement


Why “O-rings,” seals, mastics and enclosures let water in

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Almost all O rings, seals, mastics and enclosures let water in. Most of them are excellent at keeping liquid water out – but are very poor at sealing against water as a vapour as it can pass straight through the material of many seals. But how can you tell which is right for your purpose? Versaperm Limited, a world leader in water vapour permeability measurement, has introduced a quick and simple way to test this and overcome the difficulty.

Water vapour problems cost the UK over £100M damage every year.

The new Versaperm’s MKVI WVTR (Water Vapour Transmission) meter has been purpose designed for this task. It can cope with several samples, seals or enclosures at a time, often give a reading in as little as 30 minutes – whereas conventional gravimetric measurements take several days and are significantly less accurate.

Seals, mastics, adhesives, gaskets, O-rings and enclosures can be highly sensitive to changes in pressure, temperature and other conditions. Testing is the only way to ensure that a seal is fit-for-purpose and that Quality Control is being maintained.

The WVTR meter is easy to use and gives a series of digital readouts that can be saved or simply read off the screen. It needs no re-calibration and requires, at most, minimal training to give results that can be as accurate to the PPM (parts per million) or PPB (parts per billion) range depending on the gas used. The instrument can be configured to measure not just water vapour but most gaseous, including Hydrogen, Helium, Hydrocarbons, Oxygen, Nitrogen and Carbon.

As well as manufacturing the instruments, Versaperm offers a water vapour (and other gases) permeability laboratory service for companies that need to test samples on an irregular basis.

Common O Ring materials

Aflas FEPM

Resists oils, lubricants and some fuels, it is suitable for use with H2S, amines or high temperature water/steam.

Butyl IIR

Offers low gas permeability and is can be used for vacuum and high pressure applications. It should not be used with mineral oils

Epichlorohydrin ECO

Provides good resistance to mineral oils, fuels and ozone. Has poor compression set resistance.

Ethylene-propylene, EPM/EPDM

Offers excellent resistance to weathering, ozone, water and steam.

Fluoroelastomers. Dyneon, Viton, Tecnoflon

Works well in severe chemical conditions and high temperatures.

Fluorosilicone FVMQ

Is extensively used for static seals in aerospace as it is highly resistant to many hydrocarbon types.

Hypalon (and other chlorosulphonated polyethylenes)

Offers excellent resistance to weathering and works well with many media for static sealing duties.

Hydrogenated nitrile, Elast-O-Lion

Offers good mechanical and chemical resistance properties.

Kalrez FFKM

These erfluoroelastomer compounds have excellent chemical and temperature resistance (grade dependant).

Natural rubber

Strong with good abrasion resistance, it is suitable for use with ammonia, ethylene glycol, dilute acids and alkalis, though please note that synthetic rubbers provide greater resistance to heat, weathering and oils.


A general purpose elastomer that stands up well to sunlight and atmospheric ageing.


Widely used with mineral oils water and some solvents, some grades are suitable for food applications.


Offers good mechanical properties as well as resistance to weathering. hydrocarbon fuels and mineral oils. Stress relaxation may occur above +50°C.

PTFE, Fluolion

Offers excellent resistance to most media and can also be used for 'O' ring back-up rings, though flow characteristics limit its use.


Offers good heat and weathering resistance as well as having excellent electrical properties. Sealing ability is limited due to high gas permeability, low tensile strength and poor resistance to tear and abrasion.

Copyright Versaperm 2007: This table can be freely published as long as it is properly credited to Versaperm Limited


Please send any sales enquiries to Christopher Roberts, Versaperm Limited ,
10 Rawcliffe House, Howarth Road, Maidenhead, Berkshire, SL6 1AP, UK, Tel: +44 1628 777668
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For further Press Information please contact Gerry Palmer @ the Palmer & Rose Partnership. Tel 01494 637499, fax 0871 9003898,