Safety Valves With Bellows; Safety Valves With Blow-Down Ring; Safety Valves Built Into Installations; Open Bonnet - Leser 411 Instructions De Service

number of load
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
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
bonnets and bellows, the effect of the
temperature on the spring is reduced.
Corrosion effects:
•
Medium may enter into the spring chamber
if safety valves do not have bellows.
Corrosive/abrasive
fatigue strength. This should be taken into
consideration when selecting, sizing and
servicing safety valves.
•
Spring materials with increased corrosion
resistance may be used (e.g., stainless
steel, Hastelloy, ...)

10 Safety valves with bellows

The pressure and temperature application limits
of bellows must be complied with.
Defective bellows are recognisable by the
medium leaking out of the open bonnet or the
vent hole. Hazards from leaking medium must
be prevented.
Measures against leaking medium:
•
Equipping the valve with an inspection
manometer and a drip container.
•
In the case of open bonnets, the leaking of
the medium cannot be prevented if the
bellows are defective. Hazards have to be
prevented, (e.g., by a sufficient safety
distance, protection equipment or by using
only non-hazardous media).
Defective bellows
immediately in order to ensure the correct
function of the safety valve.
changes is practically
test pressure with a
cooling zones, open
media reduce the
must be replaced
Stainless steel bellows for which the number of
permitted load changes has been exceeded, or
is unknown, must be replaced. As a rule
bellows should be replaced whenever the valve
is dismantled.
Moisture or dirt must not be allowed to enter the
bonnet via the vent hole. Appropriate protective
measures (e.g., connections, pipes,...) must be
taken.

11 Safety valves with blow-down ring

Safety valves with blow-down ring, like type
526, are always delivered with the blow-down
ring in the lowest position. That is, that the
blow-down ring is screwed into the nozzle, until
the lower stop is reached. The blow-down ring
is arrested with a lock screw, which is sealed.
The position of the blow-down ring must not be
changed.

12 Safety valves built into installations

12.1 Open bonnet

For open bonnets or lever valves, appropriate
measures must be taken to avoid contact with
movable parts (e.g., the spring) as otherwise
there is a danger of jamming. Medium can
leak out of the open bonnets or open spindle
guides of lever safety valves. The user must
ensure that leaking medium cannot cause
hazards. A sufficient safety distance has to be
observed.

12.2 Regular lifting operation

Safety valves must be vented regularly in
order to check their function and to remove
residues. They can be opened if at least an
operating pressure of
pressure is reached. Exceptions can only be
allowed if the functioning is checked regularly
in a different way, e.g., by appropriate short
maintenance intervals. The valid regulations
for the application of safety valves have to be
adhered to.
After lifting, the lever must move freely, i.e.
the lifting fork in the lifting device must not
acting on the spindle cap.

12.3 Forces acting on the safety valve

Safety valves must not be subjected to
excessive static, dynamic or thermal stresses.
These can be caused by:
•
Installation under tension (static)
•
Reaction forces when blowing off (static)
•
Vibrations (dynamic)
•
Temperature expansion (thermal)
75% of the set
23
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