‘O’ MY GOODNESS
Why “O-rings,” seals, mastics and enclosures
let water in
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image
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.
|
Neoprene
|
A general purpose elastomer
that stands up well to sunlight and atmospheric ageing.
|
Nitrile
|
Widely used with mineral
oils water and some solvents, some grades are suitable for food
applications.
|
| Polyurethane |
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.
|
|
Silicone |
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
ENDS
Please send any sales enquiries to Christopher Roberts, Versaperm Limited ,
10 Rawcliffe House, Howarth Road, Maidenhead, Berkshire, SL6 1AP, UK, Tel: +44 (0) 1628 777668
e.mail info@versaperm.co.uk Web http://www.versaperm.co.uk
For further Press Information please contact Gerry Palmer @ the Palmer & Rose Partnership. Tel +44 (0) 1494 637499, fax
0871 9003898,
e.mail gerry@palmer-rose.co.uk |
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