TPi May 2017

50 / 64

48 TUBE PRODUCTS INTERNATIONAL May 2017
Fi t t ings , valves , f langes & connectors
No fear of excess pressure
Safety relief valves offer protection and aid process operability
Safety relief valves protect from
excess pressure by targeted release
of vapours and gases. David Breil,
product specialist at the German
manufacturer Witt, talks about these
passive protective devices.
Who benefits mostly from safety relief
valves?
Anyone who operates pressurised
systems, components or plants. These
valves are typically fitted onto pressurised
gas tanks or loop line systems which,
for instance, work with an operating
pressure of 16 or 25 bar. Safety relief
valves prevent serious accidents by
relieving pressure before excess pressure
can build up and become dangerous to
systems and people.
What are the dangers?
Process safety issues can exist, through
design or operation. Excess pressure
can build up rapidly and exceed the
material’s burst limit. Safety relief valves
are a last line of defence to prevent
damage.
Does this mean that safety relief valves
are only required for high pressures?
No, not at all. Excess pressure can also
have undesired consequences when
working with low pressures, for instance
below 500 mbar. In these cases, it is
less about life and limb but rather about
its effects on the quality of the products
or the devices used. I am referring to
applications such as transport receivers
for highly sensitive high-tech products,
isolator and glovebox systems or
industrial furnaces under a protective
atmosphere. Even minor pressure
fluctuations can put the process at
risk. This area in particular is where the
sensitive Witt valves of the AV series with
opening pressures of 5 mbar can prove
their strengths.
How do these safety relief valves work?
Our high quality valves are spring-
loaded and are direct acting. This
means that as soon as the opening
pressure is reached, a spring-loaded
component gives in, opens the valve
and releases the excess pressure.
It then closes automatically after
equalising the pressure. A renewed
increase in pressure will open it again.
For which pressure range can these
valves be used?
Witt safety relief valves can cover an
extremely wide operating range. The
opening pressure can be set from 5 mbar
to 45 bar, depending on the model. Thus,
evenminimal increases in pressure can be
detected. As previously mentioned, this
is important when it comes to protecting
highly sensitive systems or housings. At
the same time, they have a high venting
output of up to 970m³/h at temperatures
ranging from -60 to +270°C. Because
they are small, they can be installed just
about anywhere, and in any orientation.
However, the orientation needs to be
known in advance for safety valves in
millibar range, so that Witt can set the
opening pressure to suit the system’s
operating pressure.
You also offer special TÜV approved
valves – why is this?
Witt always checks the entire production
line before delivery, piece by piece. Each
device’s set pressure testing is witnessed
and signed off by a TÜV inspector.
Consistent with our certification to
the Pressure Equipment Directive, this
individual approval is prescribed for the
higher pressure models. However, we
also offer this service for all models in
the lower pressure range. In this way, our
customers receive an external certificate
that guarantees extra peace of mind with
regard to safety.
What other selection criteria are there
for safety relief valves?
The type of gas plays an important role.
We use brass as a standard housing
material for technical gases. In most
cases, aggressive or corrosive media
require stainless steel equipment, which
is used for securing biogas plants,
for instance. Aluminium is another
possibility. Besides the housing, even
the seals must be adapted. We have
different materials available depending
on the type of gas.
Witt-Gasetechnik GmbH & Co KG –
Germany
David Breil, specialist for safety relief
valves at Witt-Gasetechnik
Witt safety relief valves