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HYDRAULIC SYSTEM
24
Chapter 6
SAFETY VALVES
The load capacity of the safety valve must allow the discharge of a quantity of vapour, not lower than:
Q / 0,58 [kg/h]
where:
Q is the useful outlet power to the generator water expressed in kilowatt.
The diameter of the minimum net transversal section of the valve inlet must not be lower than 15 mm.
The valve load pressure, equal to the calibration pressure, increased by the overpressure, cannot exceed
the maximum exercise pressure of the heat generator.
The designer must check that the maximum pressure existing in every point of the system, does not exceed
the maximum exercise pressure of its every component.
The safety valve must be connected to the highest part of the heat generator or outlet pipes, immediately
near the generator. The length of the pipes route included between the attachment to the generator and
the safety valve must not be higher than 1 m.
The connection piping of the safety valve to the heat generator must not be traceable and must not
present, in any point, section lower to the inlet of the safety valve or the sum of the inlet sections in case of
more valves under the individual pipe.
The discharge piping of the safety valve must be realised in order not to prevent the regular functioning
of the valves and not to cause damages to persons; the discharge must fl ow immediately near the safety
valve and be accessible and visible.
The diameter of the discharge piping must not however be lower than that of the outlet connection of the
safety valve. For diameter of outlet connection it is intended the minimum internal diameter on the valve
outlet upstream of the eventual internal threading.
CLOSED EXPANSION VESSEL
The appliance must be connected directly to the vessel or to the system expansion vessels unit through a
pipe with internal diameter not lower than 18 mm.
The vessel maximum exercise pressure must not be lower than the calibration pressure of the safety valve,
increased by overpressures, characteristic of the same valve, bearing in mind the eventual level diff erence
between vessel and valve and the pressure generated by the functioning of the pump.
The capacity of the expansion vessel/s is evaluated depending on the total system capacity as results from
the project.
The closed expansion vessels must comply with the dispositions regarding the planning, manufacturing,
evaluation of conformity and use for pressure appliances. Intercepting objects or section decreases must
be inserted/practiced on the connection piping, which can be constituted by system portions.
The insertion of a three-way intercepting valve which allows connection between the vessel and the
atmosphere for maintenance operations is allowed. Such device must be protected against accidental
manoeuvres. The connection pipe must be realised in order not to present scales or deposits storage
points.
In case of more heat generators which feed the same plant or the same secondary circuit, each heat
generator must be connected directly to the expansion vessel or plant expansion vessels unit, altogether
dimensioned for the total volume of water contained in the same plant or the same independent circuit.