As the cold water is discharged from this tube into the bottom of the tank, it is heated by electric elements or a gas burner. Hot water, being lighter in weight than eold water, rises to the top of the tank where it is drawn off through an outlet tube to faucets and appliances that use hot water.
Whether water is heated by electricity or gas, the temperature of the water is controlled by a thermostat that "senses" temperature. As water heat reaches a preset temperature, the thermostat responds by closing the switch that allows the electric current to flow. When water falls below the preset temperature, the heating elements are turned back on.
About Electrically Operated Units
Two types of electrically-operated, water heaters prevail: induction and immersion.
As the term indicates, an induction type heats water by inducting heat from an electric coil. The electric coil does not come into contact with the water. Instead, the element is strapped around the outside of the tank and is covered with heavy insulation, causing heat to pass through the wall of the tank.
In contrast, an immersion water heater has the elements in direct contact with water. Elements pass right through the wall of the tank, with openings around them sealed tightly so the tank maintains its watertight integrity.
How Gas Operated Units Work
Water heaters that use gas as the heating element have as their main parts a gas burner and pilot light. The burner is positioned outside the tank — never in contact with water. Its flame is directed against the bottom of the tank so cold water being discharged from the dip tube is heated.
Water Heaters
Situated in such a position as to be kept hot at all times by the pilot light is a flame sensor. If for some reason the pilot light goes out, the flame sensor cools, and in so doing cuts off the flow of gas to theburner.
Selecting a Water Heater
If you are building a new home, remodeling an older home, or replacing a water heater that has failed, you will want to select a new heater that best meets your family's needs. The General Public Utilities Corporation has provided a guide that may be used to make a selection:
This article is mostly likely taken out of______.
A.a textbook intended for technicians
B.a consumer guide
C.a book on the history of electric appliances
D.an operation manual for a type of water heater
第2题
有关系统性红斑狼疮(SLE)的描述,错误的是
A、常有多器官受累
B、是一种具有多种自身抗体的自体免疫性结缔组织病
C、精神、神经症状表现多种多样
D、因本病所致的精神症状首选吩噻嗪类药物
E、颜面皮肤出现蝶形红斑
第5题
A.SLE是一种临床表现有多系统损害症状的慢性系统性自身免疫性疾病
B.SLE患者均有临床肾脏受累表现
C.SLE活动期补体下降
D.SLE患者血清中类风湿因子可阳性
E.SLE最常见的死亡原因是感染、肾衰竭、脑损害、心力衰竭
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