Leser 411 Instructions De Service page 22

Lubricants based on mineral oils are used as an
aid during installation. These fluids can
contaminate the medium unless special
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
E
residues containing mineral oil are removed
from the valve sufaces and special lubricants
are used.
• Bellows prevent contact between medium and
lubricant.
8 Temperatures of the medium and 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 sets of
rules and the 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.
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 taken to
ensure that the safety valve works correctly.
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Contact with hot or dangerously cold safety valve
surfaces must be prevented by 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
impaired, if the wrong spring is installed. In
extreme cases the spring will be fully
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. 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
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
number of load changes is practically impossible
to estimate.
The springs used in LESER safety valves have
been matched to the materials used in these
valves. In unfavourable cases, there may be
factors leading to increased temperature or
corrosion that make the following actions
necessary:
Temperature effects:
As spring temperatures depend on many external
conditions, no general temperature of the medium
can be specified as the limit of application. It has
to be evaluated in every single case, which of the
following measures need to be taken:
• Using spring materials that are heat resistant or
tough at subzero temperatures
• Providing the test pressure with a correction
factor to compensate for a drop of set pressure
at higher temperatures (refer to section 8 for
cold adjustment)
• By using highly heat-resistant materials in
conjunction with cooling zones, open bonnets