Safety valves for potable water heaters
A diaphragm pressure relief valve opens automatically to prevent pressure from exceeding the service pressure and closes automatically when the pressure has been reduced. Each unvented (pressurised) potable water heater should be equipped with at least one diaphragm pressure relief valve. Instant water heaters with a nominal volume below 3 litres are the exception to the rule. Only spring-loaded diaphragm pressure relief valves should be used up to a nominal volume of 5000 litres. In case of unvented potable water heaters with a nominal volume of more than 5000 litres and/or a heating capacity of more than 250 kW, the pressure relief valve has to be selected in accordance with the manufacturer's instructions. Table 1 determines the nominal size of pressure relief valves.
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