pg. 17
The safety valve
must be connected to the highest part of the heat generator or the outlet tube, next to the generator. The length of the section
of tube between the generator fitting and the safety valve must not be more than one metre. There must be no cocks that can cut off the tube
connecting the safety valve to the heat generator and the section must not be less than the inlet section of the safety valve or the sum of the inlet
sections if there are several valves that head a single tube, at any point whatsoever along its length. The outlet tube of the safety valve must be
installed in such a way that it does not prevent the normal functioning of the valves and will not cause injury to persons ; the outlet must be located
as close as possible to the safety valve and be accessible and visible. The diameter of the outlet tube must not in any case be less than the
diameter of the safety valve outlet fitting. The outlet fitting diameter is the minimum internal diameter of the valve outlet upstream from any existing
internal threading. The valve discharge pressure, equal to the calibration pressure and increased by the overpressure, must not exceed the
maximum working pressure of the heat generator. The designer must ensure that the maximum pressure existing at every point of the system
does not exceed the maximum working pressure of each of its components. The discharge capacity of the safety valve must be calculated
according to the prescriptions set out in UNI 10412/2.
The diameter of the minimum net cross section of the valve inlet must in any case be not
less than 15 mm.
The maximum working pressure of the closed expansion tank
must not be less than the calibration pressure of the
safety valve, plus the specific overpressure of the valve itself, with any difference in height between the tank and the valve taken into
account,and the pressure generated by the functioning of the pump. The capacity of the expansion tank or tanks is evaluated according to the
overall capacity of the plant as per the design. The closed expansion tanks must comply with current regulations governing pressure appliances
in terms of design, construction, conformity assessment and utilization.
The rated volume of the closed expansion tank must be sized in relation to the expansion volume of the water in the
system.
The heat generator must be connected directly to the plant’s expansion tank or group of expansion tanks with a tube having
an internal diameter no less than 18 mm. The connecting tube, which may consist of plant parts, must not be fitted with any shutoff
cocks or have reduced sections. One three-way on-off valve may be installed for connecting the tank to the atmosphere for maintenance
operations. This device must be protected against accidental manouevres. The connecting tube must be fitted in such a way that no scaling or
deposit points are created. If several heat generators power a single system or secondary circuit, each heat generator must be connected
directly to the system’s expansion tank or group of expansion tanks sized overall for the total volume of water contained in the same plant or
independent circuit. When it is necessary to separate the single heat generator from the expansion tank or group of expansion tanks, then a
three-way tap having the same characteristics as those listed above must be installed on the tube that connects the generator to the expansion
tank, in order to ensure that the generator is in any case connected either with the expansion tank or with the atmosphere in every position.
The expansion tanks, connecting tubes, the vent and smoke exhaust pipes must be protected against freezing in areas where this could occur.
The solution adopted for this purpose must be described in the project. Given that the circulation of the water in the heat generator must be
maintained in any system and in all operating conditions within the limits prescribed by the supplier of the generator, in closed expansion tank
heating systems, in which the circulation of the water is assured by means of an electric pump, the pump stopping must not cause, in any
operating condition, the temperature to rise above the limit prescribed in these instructions.
The previous chapter does not replace UNI 10412/2 to which it makes reference . The qualified installer must in any case
be fully aware of this standard and its amending versions.
4.10 INSTR
4.10 INSTR
4.10 INSTR
4.10 INSTR
4.10 INSTRUCTIONS FOR EXECUTING HYDRA
UCTIONS FOR EXECUTING HYDRA
UCTIONS FOR EXECUTING HYDRA
UCTIONS FOR EXECUTING HYDRA
UCTIONS FOR EXECUTING HYDRAULIC SY
ULIC SY
ULIC SY
ULIC SY
ULIC SYSTEM.
STEM.
STEM.
STEM.
STEM.
Instructions for closed system
Systems with closed expansion tank, must be provided with :
a) safety valve b) thermal relief valve or thermal safety outlet (positive safety )
c) closed expansion tank d) circulating pump activation thermostat (included in the panel of the central heating cooker).
e) acoustic alarm activation thermostat f) acoustic alarm
g) pressure gauge thermometer h) circulation system
These devices must be installed on the generator’s delivery tube, within not more than 1 metre from the machine.
