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Safety equipment
acc. to DIN 4751 part 2
Scope:
Sealed, thermostatically
protected heat generator systems
with flow temperatures up to 120 °C.
Safety valve
Diaphragm
Blow-off output in kW
safety valve
Size, internal diameter, DN
Fitting thread for supply line
Fitting thread for blow-off line
Expansion vessels
Low water indicator
Safety equipment
Thermometer
Heat. circ. pump
Safety valve
Open flash trap
Low water indicator
Maximum pressure
limiter
Pressure
gauge
Every boiler must be protected against exceeding the permissible operating pressure
by a diaphragm safety valve or other spring-biased safety valves. Safety valves must
comply with TRD 721. A maximum of three safety valves may be applied to each heat
generator. A flash trap must be installed immediately next to each safety valve for
boilers with a rated output in excess of 350 kW. The installation of flash traps is not
required for hot water heating systems, if each heat generator is equipped with one
or an additional STB and one or an additional pressure switch.
Sizes and internal diameters of diaphragm safety valves, dimensions of supply lines
and blow-off lines.
The water and gas chamber of pressure expansion valves must be calculated in
accordance with DIN 4807 part 2.
If the permissible operating pressure is lower than the highest working pressure of
the pressure dwell valve, protect the expansion vessel by suitable type-tested safety
valves against excessive pressures. Size open expansion vessels for a minimum
pressure of 2 bar.
Arrange all expansion vessels with shut-off facilities towards the heating system.
Ensure that the shut-off equipment is sufficiently protected against unintentional
closure (e.g. cap valve protected with a wire and seal).
Equip each boiler with a type-tested low-water indicator. A low-water indicator is not
required for boilers up to 350 kW, since excessive heating at low water conditions is
prevented. This was verified as part of the type testing of the STB installed in the control
unit.
50
100
200
15
20
25
G ½"
G ¾"
G 1"
G ¾"
G 1"
G 1¼"
Heat consumer
External pressure
monitoring
Fresh air
ventilation/
exhaustion
Cap valve
Expansion vessel
Drain valve
Minimum pressure
switch
Boiler fill and drain valve
350
600
32
40
G 1¼"
G 1½"
G 1½"
G 2"
13
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