2.3 PLUMBING FIXTURE
Each hot service water pressure heater must have a membrane spring loaded with a safety
valve. Nominal clearance of safety valves is defined by standard. Heaters are not equipped
with a safety valve. The safety valve must be easily accessible, as close to the heater as
possible. The inlet pipes must have at least the same clearance as the safety valve. The
safety valve is placed high enough to secure dripping water drain by gravity. We recommend
mounting the safety valve onto a branch pipe. This allows easier exchange without having to
drain the water from the heater. Safety valves with fixed pressure settings from the
manufacturer are used for the assembly. Starting pressure of a safety valve must be identical
to the maximum allowed heater pressure and at least 20 % higher than the maximum
pressure in the water main (Table 3). If the water main pressure exceeds such value, a
reduction valve must be added to the system. No stop valves can be put between the heater
and the safety valve. During the assembly, follow the guide provided by the safety
equipment manufacturer.
It is necessary to check the safety valve each time before putting it into operation. It is
checked by manual moving of the membrane from the seat, turning the make-and-break
device button always in the direction of the arrow. After being turned, the button must click
back into a notch. Proper function of the make-and-break device results in water draining
through the safety valve outlet pipe. In common operation, such a check needs to be
implemented at least once a month, and after each heater shutdown for more than 5 days.
Water may be dripping off the drain pipe of the safety valve; the pipe must be open into the
air, pointed down; environment temperatures must not drop below zero. When draining the
heater, use the recommended drain valve. First, close the water supply into the heater.
Please find necessary pressure values in the below Table 3. For proper safety valve operation, a backflow
valve must be mounted on the inlets pipes, preventing spontaneous heater draining and hot water
penetrating back into the water main. We recommend that the hot water distribution from the heater was
as short as possible to minimise heat losses. At least one demountable joint must be mounted between the
tank and every supply pipe. Adequate piping and fittings with sufficiently dimensioned maximum
temperature and pressure values must be used
Table 4
ALLOWABLE
SAFETY VALVE
OPERATING
START-UP
OVERPRESSURE
PRESSURE
OF WATER
[MPa]
HEATER [MPa]
0,6
0,7
1
MAXIMUM
PRESSURE IN
COLD WATER
PIPES [MPa]
0,6
up to 0,
4 8
0,7
up to 0,56
1
up to 0,8
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