Human beings have been exposed to natural sources of ionizing radiation throughout history, including cosmic rays and radiation produced by radionuclides on the earth. The collective radiation dose to humans comes mainly from natural background radiation and medical treatment. At present, the three principles of radiation protection generally adopted in the world are: the legitimacy of practice, the optimization of the protection level and the personal dose limit. International basic safety standards stipulate that the personal dose limit for public exposure is 1 mSv per year, while the personal dose limit for occupational exposure is 20 mSv per year. Nuclear radiation symptoms Nausea and vomiting are the earliest symptoms of typical radiation sickness. The more radiation dose, the earlier these symptoms appear. Radiation can damage hair follicles. Sometimes, this hair loss is permanent. Radiation sickness can cause oral ulcers. More symptoms include: spontaneous bleeding; hemorrhagic diarrhea; skin loss; severe fatigue; infection. Nuclear radiation may cause major diseases: leukemia, thyroid cancer, multiple myeloma, benign and unexplained tumors. Valves are found in virtually every industrial process, including water and sewage processing, mining, power generation, processing of oil, gas and petroleum, food manufacturing, chemical and plastic manufacturing and many other fields. Stop Valves, Ball Cock, Angle Valves, Gate Valves, Check Valves ZHEJIANG KINGSIR VALVE CO., LTD. , https://www.kingsir-valves.com
People in developed nations use valves in their daily lives, including plumbing valves, such as taps for tap water, gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, and poppet valves in car engines.
In nature there are valves, for example one-way valves in veins controlling the blood circulation, and heart valves controlling the flow of blood in the chambers of the heart and maintaining the correct pumping action.
Valves may be operated manually, either by a handle, lever, pedal or wheel. Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.
More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements.