Common electric water heater, there are two: one is the export of open type electric water heater is a closed electric water heater can be multi-channel water supply. Both the main structure of the electric water heater exactly the same, just different way out of the water control, and this different function and working conditions on the pressure produced a lot of differences so that the two electric water heaters. Is not the same on the safety performance requirements. At present, the home closed electric vacuum tube solar water heater  on the market is big into the water heater and water heaters.
       First, on the open
       Export open type electric water heater control mode, belonging to the former standard, that is installed on the inlet valve to control the influent and effluent of the water heater. Because of this water heater outlet open to the atmosphere, so the water heater barrel is exposed only to the internal static pressure of water. You can say there is no pressure requirements. When filled with water heating, water heating volume to be expansion of the water drip out from the outlet is a normal phenomenon.
     
       Closed electric water heater control, belongs to the latter standard, that is, through the valve in the outlet pipe to control the influent and effluent of the water heater. Because of this water heater water must be in the normal open state, so when filled with water, close the valve, the barrel is necessary to withstand the same pressure and water pressure. Actually closed water heater barrel is a pressure vessel, so that its rated working pressure and pressure must be agreed in order to ensure the normal and safe operation. This national standard (GB4706.12-1995) provides: closed electric water heater minimum rated working pressure of 0.6MPa, the provisions of the pressure value of twice the rated working pressure. At present, the market closed electric water heater, most rated working pressure set at 0.6MPa and 1.2MPa pressure test to the factory. In this way, the safety of the water heater pressure has been guaranteed.
       How the closed electric water heater under the rated working pressure of work? This task is completed by the safety valve installed in the inlet. The safety valve is actually a one-way valve and a pressure relief valve combination. The check valve also called a check valve, so that water can only enter can not leave. So that the barrel pressure is greater than the water pressure can prevent the hot water flowing into the cold water pipe in the water when the accident without water, to prevent the hot water drain. One-way valve so that the water heater inside the barrel to become a closed system. When the water heater filled with water is heated, the barrel the pressure will rise. Relief pressure of the pressure relief valve is set slightly higher than the rated working pressure is generally set at about 0.7MPa. In this way, once the barrel pressure exceeds the set pressure, there will be a part of the outflow water from the overflow of a safety valve and the barrel pressure drops below the set pressure. Safety valve overflow water drip, indicating that the pressure relief valve during normal operation.
        National standard electric water heaters for Class I appliances with the product that is in addition to basic insulation plus grounding protection, and this developed a rigorous testing standards. For standard basic insulation requirements of the electric water heater insulation resistance must be large 2MΩ general manufacturers regard this indicator set in more than 10 MΩ. The second requirement is that the 1250V voltage between live parts and the shell of the electric water heater with a minute electric strength test. In the test, you can not discharge and flashover. Voltage, 1500W electric water heater leakage current must be less than 1.1mA, so the insulation level is by no means an electric shock. However, in order to more insurance purposes, the standard also provides for electric water heater must be very harsh, wet test, electric water heaters placed in a relative humidity of 93 ± 2% of the wet room seven days, and then tested on the above indicators, the indicators must all qualified to be adopted. In ground fault protection, the standard specifies the contact resistance of the grounding of the electric water heater must be less than 0.1Ω, once the basic insulation destruction, a good grounding will protect insurance blown to prevent electric shock. This electric water heater must be used to power with ground fault protection.
        Household electric water heaters, heating temperature control installed in the water heater thermostat and temperature limiter. Thermostats are generally set in a metal tube into the water, the highest temperature control is usually set between 70-80 ° C, so you can ensure that water heaters have a greater heat storage capacity, at the same time that does not occur when something is wrong severe burns. In order to ensure the failure of the thermostat heating is not out of control, temperature limiter installed in the still chinese solar water heater , the temperature limit value set at slightly higher than the highest control of the thermostat temperature, once the heating temperature reaches the set value, the limit The thermostat will cut off the power immediately, to avoid the heat out of control, causing the accident.