172-65627M-09 (SQ10) 18 Oct 2021
24
Safety Function (Abnormal Temperature Rise
Preventing Function)
The safety function (abnormal temperature rise preventing function) activates when
the water temperature exceeds, or is expected to exceed, the allowable upper limit
temperature, in order to prevent an excessive temperature rise. This function
activates under either of the following conditions 1. or 2.
1. When the water flow rate is below than the set flow rate*:
Below the set flow rate, the control valve (No. 11) is more likely to experience
hunting (the valve is unable to control flow). As a result, not only will the water
temperature become unobtainable, but there is the danger that the water
temperature will rise suddenly.
The set flow rate of the unit varies depending on the usage conditions. Although the
flow rate is set by the value stated in the 'product specification document' at the time
of shipment, the approximate setting value per unit is approx. 2. to 4 m
3
/h.
2. When the water temperature exceeds the alarm value set at the High
Temperature Alarm for the time set as the High Temp Alarm Delay or longer.
3. When the safety function is activated:
(1) The following actions are taken to prevent an abnormal temperature rise
when under conditions described in 1. or 2. while the unit is in automatic
operation:
a) Steam will be shut off:
The motorized valve (No. 12) of the steam supply unit and the control
valve (No. 11) will close.
b) The cooling circulation system will start operation (when the cooling
circulation unit (optional) is installed):
The solenoid valve (option: No. 7) of the cooling circulation unit opens
and the circulating pump (option: No. 6) starts to operate. When the
valves etc. on the hot water outlet line are shut off, the water
discharged by the circulating pump will circulate the heat exchanger
and water stored inside. When using water on the outlet side, the
water discharged by the circulating pump will flow to the hot water
outlet side and water as a priority.
(2) When both conditions 1. and 2. have been resolved, the motorized valve
and control valve on the steam supply unit will recover (open), the solenoid
valve on the cooling circulation unit will close, the circulating pump will
stop (when the cooling circulation unit (optional) is installed) and the unit
will return to normal automatic operation after the alarm delay time**.
4. When the safety function activates frequently:
It is assumed that the water flow rate is close to the set flow rate or the
fluctuation is large. Either correct the system or consider measures to stabilize
the water flow rate.
*The set flow rate of water is the minimum controllable flow rate for the unit under operating
conditions. (Factory setting: see 'product specification document'.)
**
Alarm delay time is the time required to reach stable flow after water begins to flow, or the
time required for the circulating pump to operate to prevent overheating when the water
flow stops. (Factory setting: 5 seconds).
