Assessments - 1, GPA: 4
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Facilidade de uso
If the storage appliance is completely filled with water it is under continual mains pressure. When hot water is tapped off the appliance, cold water is immediately introduced. Turbulence strips are placed in the fire tubes for the efficient transfer of heat. The flue gases pass their heat to the water by conduction and radiation. The flue gases are led to the flue via the top box. The burner bed consists of a number of bar burners. An injector is screwed into the manifold ahead of each burner, which ensures correct mixing of gas and primary air through injection into the burner inlet venturi. Secondary air is drawn between the bar burners. An air distribution plate, which also functions as a radiant heat shield, is fitted below the burners. Any condensation water produced is captured beneath the combustion chamber and led away via a siphon (see illustration 1). 1.2 Technical safety equipment 1.2.1 Gas control The water heaters are equipped with a gas control valve which regulates the flow of gas to the burner. The combination gas control is equipped with a safety valve, gas control valve, pilot safety valve and burner control (on a standard natural gas setting) 1.2.2 Control box For safety purposes, water heaters are always fitted with three thermostats: a control thermostat, a high-limit thermostat and an overheat thermostat. The desired water temperature is set with the control thermostat. To protect against freezing, the control thermostat is also fitted with frost protection which ignites the burner when the water temperature drops to 20oC, irrespective of the thermostat’s temperature setting. The overheat thermostat prevents the water reaching too high a temperature. Should both control and high-limit thermostats malfunction, the overheat thermostat will automatically shut down the water heater. The control thermostat can be set at settings 1-4 (approx. 40°C to 73°C). The frost protection ignites the burner if the water temperature drops below 20°C. The switch temperature of the high-limit thermostat is 84°C; the overheat thermostat cuts in at 93°C. The sensor for the control/frost thermostat is located at the level of the control switch; the sensors for the high-limit and overheat thermostats are located near the top of the water heater. The control box is fitted with an ON/OFF switch (I/0). At setting I, the gas control operates on the basis of heat demand from the control thermostat. At setting 0 the water heater is switched off. The burner will only ignite on the basis of heat demand from the frost protection. When the control thermostat calls for heat, the water heater checks all controls are in the off position. Power is then switched to the ventilation fan. Immediately the air pressure switch opens. The purge cycle starts. This runs for between 30 and 60 seconds after which the safety valve opens and the spark generator is operated. Gas flows to the pilot burner where it is ignited by the spark generator. The ionization probe now detects the flame, switches off power to the spark generator and opens the main gas valve.A softlite staged ignition control prevents explosive ignition by allowing a small percentage of total gas rate into the combustion chamber initially followed by the full rate when combustion is established. When the water temperature reaches the set point the water heater is turned off. If the flame extinguishes whilst in operation both the safety (pilot) valve and the gas valve will close immediately. If the control thermostat is still calling for heat the burner automation will repeat the ignition procedure. -If no flame is detected within the safety time of 50 seconds, the burner automation will interlock and the reset knob will light up. -As long as the air proving switch does not operate (remains closed), the burner automation will remain in the waiting position, while the ventilation fan continues to work. -An interlocking of the burner automation can be cancelled out by pressing the reset knob. If the procedure does not succeed immediately, wait at least 15 seconds before pressing the interlocking knob again. If the flame detection falls out during normal operation, the burner automation will automatically repeat its ignition procedure. As long as a flame is detected within the safety period of 50 seconds, the automation will continue to repeat the ignition procedure. As soon as the water temperature has reached the set value, the burner automation will close the gas valves. The control column has a potential-free contact for external error message. 1.2.3. Ventilation fan The ventilation fan is installed in the top-box. When heat is required the ventilation fan is switched on by the burner automation. The fan switches off when the main burner has extinguished. The fan can be removed from the top box via the access panel. 1.2.4 Air proving switch The air proving switch ensures that there is sufficient air flow for the safe operation of the water heater. If the airflow falls...
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