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Chemical acid and alkaline liquid, what valve to use?

In chemical production and many areas involving acidic and alkaline liquids, the importance of the correct choice of valves for acidic and alkaline liquids is self-evident. First of all, acidic and alkaline liquids have a strong corrosive, if the valve is not selected properly, it is easy to be corroded and damaged, resulting in liquid leakage. According to relevant statistics, about 60% of the damage to chemical equipment is caused by corrosion, and the valve as a key control component, once the leakage, not only affects the production efficiency, but also may cause serious damage to the equipment, and even cause safety accidents.

For example, in sulfuric acid medium, different concentrations and temperatures of sulfuric acid on the material corrosion differences. For the concentration of more than 80%, the temperature is less than 80 ℃ of concentrated sulfuric acid, carbon steel valves and cast iron valves have better corrosion resistance, but is not suitable for high-speed flow of sulfuric acid. And ordinary stainless steel valves for sulfuric acid medium is also limited, this time the pump and valve conveying sulfuric acid is usually made of high silicon cast iron or high alloy stainless steel valves, or fluorine plastic lined with fluorine valves of this more economical choice.

In hydrochloric acid medium, most of the metal materials are not corrosion-resistant, rubber-lined valves and plastic valves are a better choice, but when the temperature exceeds 150 ℃ or the pressure is greater than 16 kg, these valves can not be competent, at this time you can consider the ceramic ball valve.

一、Common acid and alkaline liquid valve types

（一）Fluorine-lined valves

Fluorine lined valve adopts special moulding process to make the sealing surface dense and good, plus V type PTFE packing combination makes the valve reach zero leakage. With good chemical stability, suitable for any strong corrosive chemical media, such as polyperfluoroethylene FEP (F46) can be resistant to dilute or concentrated inorganic acids, alkalis, ketones and other media, the use of the temperature of - 85~150 ° C, mechanics, electrical properties and chemical stability is basically the same as F4, the outstanding advantage of high toughness of the dynamic impact, good weathering and radiation resistance.

Polytrifluoroethylene PCTEF (F3) can withstand a variety of organic solvents and inorganic corrosive fluids, the use of temperature - 195 ~ 120 ℃, heat resistance, electrical properties and chemical stability is second only to F4, mechanical strength, creep properties and hardness than F4 better. Fluorine lined valves are widely used in food, environmental protection, light industry, petroleum, paper, chemical, textile, electric power and other industries in automatic regulation and remote control system, can be used to control the opening and closing of a variety of strong corrosive media, such as in the petroleum, chemical, dyeing and chemical, acid alkali and other industries is the ideal choice.

（二）Stainless steel valves

Different stainless steel valves have different performance in acid and alkaline liquids.304 stainless steel valves have some corrosion resistance to some acid and alkaline liquids, but have limited performance in some strong corrosive environments.316 stainless steel valves contain molybdenum and have good corrosion resistance to nitric acid, but are not superior to ordinary stainless steel valves in some cases. For high temperature and concentrated acetic acid or other corrosive media containing other demanding requirements, 316 stainless steel valves containing molybdenum can also be applied to high temperature and dilute acetic acid vapour. However, stainless steel valves are not a universal material, in the selection of specific acidic and alkaline liquid media and environmental conditions for consideration.

        (三) Ceramic Ball Valves

Ceramic ball valves have significant advantages in high temperature, high pressure acidic and alkaline liquid environment. Ceramic material hardness, wear-resistant, service life can reach the metal ball valve more than 3 times. Its high temperature performance, special ceramics are usually sintered at more than a thousand degrees under high temperature, stable performance. At the same time, the ceramic ball valve corrosion resistance, chemical stability, it is difficult to chemical reaction, has a strong resistance to acid and alkali corrosion. In addition, ceramic ball valve has good sealing, thermal expansion and contraction is not obvious, can avoid material leakage. And it does not rust and operates smoothly. However, ceramic ball valves are more expensive, which is its shortcoming.

(四) Plastic valves

‘UPVC Butterfly Valve’

Take PVC electric ball valve as an example, it is all made of reinforced UPVC material, which is light in quality, good in sealing and easy in maintenance. It has the characteristics of simple structure, small size and light weight, saving material and cost. Good sealing performance, can be used in easy corrosion and different temperatures, flexible and convenient to use, and longer life.UPVC electric ball valves are usually used in blocking or circulating pipelines to control and regulate the flow of gases and liquids, and can be used for ordinary pure water, raw water, drainage systems, dirty water, water and seawater containing salts, acid and alkali chemical solution systems, etc., with a wide range of applications. But in the installation and use should pay attention to the bolts should be tightened, otherwise it is easy to leak, and only applies to open or close the flow of fluid, for flow regulation is not very obvious.

二、Basis for selection

1、The nature of the liquid: different acidic and alkaline liquids on the corrosiveness of the valve material is different. For example, sulfuric acid medium, the concentration of more than 80%, the temperature is less than 80 ℃ of concentrated sulfuric acid, carbon steel valves and cast iron valves have better corrosion resistance; for hydrochloric acid medium, the vast majority of metal materials are not corrosion-resistant, rubber-lined valves and plastic valves is a better choice.

2、Temperature: Temperature has a great influence on the selection of valves. Generally speaking, fluorine plastic valves can withstand - 85 ~ 150 ℃ temperature range; polytrifluoroethylene PCTEF (F3) can withstand - 195 ~ 120 ℃ temperature. For high temperature environments, such as high temperature nitric acid, titanium and titanium alloy materials are usually used; for high temperature and high concentration of acetic acid, high alloy stainless steel valves or fluoroplastic valves can be used.

3. Pressure: pressure is also an important factor in selecting a valve. When the pressure is too high, some plastic valves may not be able to handle. For example, in the pressure is greater than 16 kg, ordinary plastic valves, including polypropylene, fluorine plastic and even PTFE can not be used, then you can consider ceramic ball valves or other more pressure-resistant valves.