Product Overview

“Legionella” - Scalding risk
In systems producing domestic hot water
with storage, in order to avoid the dangerous
bacteria known as ”Legionella”, the hot
water must be stored at a temperature of at
least 140°F. At this temperature it is certain
that the growth of the bacteria causing this
infection will be totally eliminated. However,
at this temperature the water cannot be
used directly, as it may cause scalding. For
example, at 130°F, partial burning takes
place in 30 seconds and at 140°F total
burning takes place in 5 seconds.
In view of the above, it is necessary to install a
thermostatic mixing valve which can :
· reduce the temperature at the point of use
to a value lower than that of storage;
· maintain this value when the incoming
pressure and temperature conditions
vary.
Thermal disinfection
The diagram below shows the behavior of
the bacteria “Legionella Pneumophila” when
the temperature conditions of the water
in which it is contained vary, in laboratory
sample population.
In order to ensure proper thermal
“disinfection”, the value must not be below
140°F.
Reference documents
For the prevention and control of Legionella,
see the National Regulations and applicable
Code of Practice.
32
60
80
100
120
140
160
Kills bacteria instantly
Kills 90% of bacteria in 2 minutes
Kills 90% of bacteria in 2 hours
Optimum temperature
for growth of bacteria
Surviving bacteria inactive
Principle of Operation
A thermostatic mixing valve mixes hot and cold water in such a way as to maintain a constant
set temperature of the mixed water at the outlet.
A thermostatic element is fully immersed into the mixed water. It then contracts or expands
causing movement of the piston, closing either the hot or cold inlets, regulating the flow rates
entering the valve. If there are variations of temperature or pressure at the inlets, the internal
element automatically reacts attempting to restore the original temperature setting.
Thermal shutoff
In the event of a failure of either the hot or cold supply, the piston will shut off, stopping water
discharging from the mixed water outlet.
The Caleffi valve requires a minimum temperature differential from hot inlet to mixed water outlet
of 20°F (11°C) to ensure the correct operation of the thermal shutoff feature.
Construction details
Double seat
The mixing valve has a special actuator which acts on a double water passage seat. This
produces a high flow rate with a reduced resistance, at the same time maintaining accurate
temperature control.
Anti-wear surfaces
The materials of construction in the 5231 series thermostatic mixing valve eliminates the
problem of jamming caused by mineral deposits. All the working parts, such as the PPSG40
shutter and EPDM seals, are made of a special anti-scale material, with a low friction coefficient,
providing long term high performance.
Low inertia thermostat
The temperature-sensitive element, the “motor” of the thermostatic mixing valve, is characterized
by a low heat inertia; this means that it reacts rapidly to variations in the incoming temperature
and pressure conditions, reducing the valve response times.
Temperature setting and locking
The control knob permits temperature setting, between min. and max., in one turn (360°). It
also has a tamper-proof system to lock the temperature at the set value.
HOT
MIXED
COLD