Safety valve heating and electric water heater with hot water leakage when no one

If this situation is normal, as mentioned above, when no hot water, electric water heater there is equivalent to a closed system, this time inside the water is heated, temperature, volume expansion, but because electric water heater tank volume is constant, there is no place to absorb the expansion water, so the water pressure inside the water heater will be increased when the pressure is greater than the take-off when the pressure relief valve, pressure relief valve will take off within the protection of the water heater bile, is what we see in the drip valve. If you want to in this case the safety valve is not dripping, you can install an expansion tank in the Italian Akusitan pipeline between the safety valve and the water heater to absorb the amount of expansion produced after water is heated, the heating time electric heater, water pressure will not rise much;