The purpose of supervising phosphrate of boiler water: The boiler water must keep a certain amount of phosphate, mainly in order to prevent the generation of calcium scale. The phosphoric acid root in boiler water should not be too low or too high, If it is too low, it will not react with calcium ion to generate soft water slag that can be drained regularly. If it is too high, PH value of phosphate in boiler water increases, the blowdown of the boiler increases, the heat loss is high and the dosage increases, etc., which is not conducive to economic operation. 

The purpose of supervising PH value of boiler water: The PH value of boiler water shall be greater than 9, if it is less than 9, which will cause the steel of the boiler to be corroded; Only under the condition that PH value is enough high, can the reaction of phosphate and calcium phosphate generate the water slag that can be easily drained. But PH value cannot be too high, otherwise the free sodium hydroxide in boiler water will be more, which will cause alkaline corrosion. The silicate is hydrolyzed in boiler water, so the capacity of silicate in steam is reduced. 

The purpose of supervising the salt content and silicon content in boiler water: In order to ensure that the steam quality. Because the water is carried by the steam, the sodium salt and silica acid in boiler water are carried into the steam. When then salt content in boiler is within a certain range, the water carried by the steam is basically definite. But when the salt content and silicon content are more than a certain value, the steam carried by water will increase obviously, making the steam quality significantly worse. 

When the salt content in boiler water increases to a certain amount, the boiler water viscosity increases, the small bubbles in boiler water are not easy to grow up, the foam layer may be produced at the same time, thus making the increasing of water carried by the steam and the increasing of salt content in steam. In high pressure boiler, there is a phenomenon that the steam has selective solubility carrying to some substances (silicate) in water, which is also known as selective carrying. The selective carrying amount of the steam to silicate is directly proportional to the carrying amount(capacity) of the silicate in boiler water. Namely, the greater the silicon content in boiler water is, the greater the silicon content in steam is. If the silicon content in steam is beyond the standard, which may easily cause SiO2 to deposit in steam turbine. 

The purpose of supervising basicity in boiler water: When the basicity in boiler water is too high, it may cause the alkaline corrosion and stress corrosion fracture of boiler water -cooled wall tube and may make the boiler water produce bubbles and affect the steam quality. 

Monitor CI in boiler water- If the chloride exceeds the permitted standard, it will destroy the protective film on the surface of the water-cooled wall tube and cause corrosion. If the steam carrying chlorine ions enters into the steam turbine, which will can cause stress corrosion of high-grade alloy steel inside the steam turbine.