Functional Tightness Of A Safety Valve; Medium - Leser 411 Instructions De Service

35% of the set pressure by using stainless steel
bellows specially designed for this, which
compensates the force acting on the rear side
of the disc. Function and set pressure remain
constant. If it is not clear whether the bellows
compensate for pressure, LESER should be
contacted. The application limits of the bellows
for pressure and temperature must not be
exceeded (refer to section 10).
If discharge lines are fitted with equipment,
which prevents the ingress of rainwater or
foreign bodies, such equipment must not
obstruct or restrict the outlets of the safety
valve.
The blow-off pipe should be dimensioned using
the maximum back
appropritate temperature. It should be installed
in a pipe run, which is free from restrictions and
turbulences and should not be opposite other
branches, to ensure that it does not impair the
functioning of the valve or damage it. The
capacity and functioning of safety valves must
also be ensured in applications, where blow-off
systems fulfill several functions.
During blowing-off, reaction forces act on the
safety valve itself, the pipes connected to it and
the fixed mounts. The size of the reaction force
is particularly important for the dimensioning of
the fixed mounts.
The following points have to be taken into
consideration:
•
Static, dynamic or thermal loads exerted by
the pipe leading to or from the safety valve
must not act on the valve.
•
Safety valves must be fixed as specified in
the drawing. Omitting or removing mounts
can result in damage because this results in
excessively large forces or tensions.
•
Also refer to section 12.3.
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Functional tightness of a safety valve

One has to expect a slight leakiness with all
safety valves fitted with metal seals. People,
environment and installations must not be
endangered by the escaping medium.
Safety valves with soft seals seal are much
more reliable than those with metal soft seals.
LESER offers a range of elastomer materials
for different applications. The elastomers must
match the medium and its pressure and
temperature.
All LESER products are inspected for damage
and leaks. In order to prevent damage during
transport all products have their flange faces,
pressure and the
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sealing lips and pipe threads protected before
being packed for shipment. This protection
should be removed before assembly (refer to
section 12.12).
Before installing the valve in the plant or
pipeline system it should be inspected for
damage. Once installed, the valve should be
checked for leakage while the plant or pipeline
system is operating.
Sealing surfaces are machined with great
precision. A tight seal is achieved, for instance,
by hardening, tempering, precision-grinding and
lapping. This makes safety valves vulnerable to
impact damage; they may, for example,
develop leaks as a result of vibrations.
The following notes are to be observed:
•
During transport, installation and operation
safety valves must be protected from
vibrations.
•
Safety valves must be transported with
care, e.g., the lever must never be used as
a carrying handle and the safety valve must
not be dropped.
The force between the seat and the disc falls as
a function of rising
Therefore the probability of leaks also rises if
the operating pressure is close to the set
pressure (refer to section 4). Damaged or
contaminated sealing surfaces in particular tend
to develop leaks.

Medium

Any moving parts have to be protected from
abrasive/corrosive media to avoid the risk of
jamming, seizing or sticking. This can be done
by servicing the valve each time it has opened
or by using stainless steel/elastomer bellows.
The limits of application for the bellows have to
be observed.
The possibility of leaking sealing surfaces
caused by abrasive media must be considered.
Dangerous media must not be allowed to enter
the environment. In case of doubt the safety
valve should be replaced after opening.
Soft sealing discs can compensate for minor
damage to the seat. In every case the limits of
application and medium consistency for the
elastomer material have to be observed.
The strength of components (e.g. body, spindle,
spring) may be reduced by abrasion. This may
lead to leaking or to the bursting of pressure
equipment. If abrasive
maintenance intervals should be shortened.
operating pressure.
media are used,
21
E