Temperatures Of The Medium And Ambient Temperatures; Choice Of Spring - Leser 411 Instructions De Service

Sealing surfaces must not stick together.
This can be prevented by:
•
Regular lifting operation (refer to section
12.2)
•
Heating or cooling to prevent the seat from
sticking
•
Other measures which prevent sticking.
E
Corrosion damage to body parts and inner parts
cannot always be spotted easily. Therefore the
user must make sure that the medium does not
attack or corrode the materials the safety valve
is made from. If this possibility cannot be
excluded, monitoring and servicing have to be
adapted to this situation accordingly. Special
materials can be selected on request.
Lubricants based on mineral oils are used as an
aid during
contaminate
precautions are taken.
The following points have to be observed:
•
Lubricants/auxiliary fluids can reach the
medium and contaminate it or cause a
chemical reaction.
•
Lubricants can be washed out and make
the dismantling of the safety valve more
difficult.
•
Safety valves can be designed as oil and
grease-free types. For these types of valves
all residues containing mineral oil are
removed from the valve sufaces and
special lubricants are used.
•
Bellows prevent contact between medium
and lubricant.
8 Temperatures
ambient temperatures
Minimum and maximum temperatures are given
for LESER safety valves. They always refer to
the temperature of the medium, which may
simultaneously be the ambient temperature.
Therefore, the ambient temperature has to be
taken into consideration under extreme climatic
conditions such as are found in Scandinavia.
It is necessary to observe the effect of
temperatures of the medium on the maximum
permitted pressure. If expansion limits drop at
higher temperatures or if the medium tends to
be brittle at low temperatures, the maximum
permitted temperatures must be lowered.
Please observe the specifications/regulations in
the appropriate
manufacturer's specifications.
If the safety valve is supposed to be thermally
insulated, the bonnet and the cooling zones (if
there are any) must not be covered to protect
the springs from becoming overheated.
22
installation. These fluids
the medium unless
of the medium
sets of rules and
To set a safety valve for a particular pressure at
a higher ambient temperature, a correction
factor should be used to allow for the increased
temperature. This eliminates the necessity of
adjusting the setting while the medium is at the
higher temperature (procedure: Cold differential
test pressure according to LESER work
standard LWN 001.78).
During the operation of safety valves, medium
can freeze, which prevents opening and
closing. This can happen if the temperature falls
below the freezing point of the medium. In case
of media, which congeal at low temperatures,
the viscosity may drop significantly. If the
medium contains freezing vapours, the risk of
icing-up is increased by the expansion of gases
as this causes the temperature to fall further. If
there is danger of icing, measures must be
can
taken to ensure that the safety valve works
special
correctly.
Contact with hot or dangerously cold safety
valve surfaces
appropriate protective measures.
9

Choice of spring

The springs used by LESER are designed for
defined pressure ranges. The test pressure is
always the basis for selecting the spring (refer
to section 4). The functioning of the springs is
ensured if the spring is designed and used in
conformity with the sets of rules.
When dismantling the valves, the springs must
not be mixed up as the functioning will be
and
impaired, if the wrong spring is installed. In
extreme
compressed (the coils touch each other) and
the safety valve does not work.
When changing the test pressure the user must
check whether the spring/springs can be used
at the new pressure. This can be done by using
current LESER spring tables (LWN 060.xx).
If they are not available please contact LESER.
If the spring is not suitable for the new test
pressure it must be replaced by a suitable
spring. If the test pressure of a safety valve is
altered, the whole safety valve and its
dimensioning must be checked for suitability.
LESER springs bear clear identification marks.
Springs which can no longer be identified or
the
damaged springs must not be used.
Springs must not be reused if it cannot be
estimated how many load changes they have
been subjected to. This applies in particular to
the springs of safety valves which have been
exposed to vibrations, as in this case the actual
must be prevented
cases the spring will
by
be fully
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