Cast steel has less carbon content and good toughness, so steel is more widely used than pig iron. Steel not only has good plasticity, but also steel products have high strength, elongation and other mechanical properties, which are better than cast iron. Ductile iron in cast iron is a kind of high strength cast iron material developed in the 1950s. Its comprehensive properties are close to steel, which is based on its excellent properties, It has been successfully used to cast some parts with complex force and high requirements of strength, toughness and wear resistance. Nodular cast iron has rapidly developed into a widely used cast iron material next only to gray cast iron. The so-called "replacing steel with iron" mainly refers to ductile iron.

Because of the different types of steel used, the medium used for steel valves is also very different. Although the price of steel valves is relatively expensive, steel is a plastic material and can be used in a variety of media, such as saturated steam and hot steam, high temperature and low temperature oil products, liquefied gas, corrosive medium, etc., so it is widely used.
Carbon steel, because of its excellent mechanical properties and comprehensive use performance, it has a wider range of use, usually including cast iron valve and bronze valve (widely used under - 180 ℃) operating conditions. Generally, the steel valve with strong reliability is used in important equipment, equipment and pipeline. Steel valves must be used in pipelines with combustible gas, liquid, toxic gas, liquid, inflammable and explosive medium, compressed gas, liquefied gas, power plant and other similar occasions.
The special carbon steel and low nickel alloy steel can be used in the working condition with the working temperature lower than zero, but can not be used in the area of deep cold. Valves made of these materials may be suitable for seawater, carbon dioxide, acetylene, propylene and ethylene.
Corrosion resistant steel includes stainless steel, special stainless steel, Monel alloy, hastloi "B", Hastelloy "C", stainless steel and acid resistant steel. Stainless steel acid resistant steel valve can be widely used in chemical and food industries. For example, the pipeline for transporting acetic acid, nitric acid, sulfuric acid, alkali, bleach, food, juice, carbonation, tannery liquid and many other chemical products. Ultra low carbon austenitic stainless steel valves are usually used to transport liquid gases such as natural gas, biogas, oxygen and hydrogen at low temperature. Special stainless steel valve has good corrosion resistance, and is usually used in the pipeline and equipment for conveying sulfuric acid of various temperatures and concentrations“ Monel alloy valve is mainly used for conveying alkali, salt solution, food and many inorganic acids, especially sulfuric acid and hydrofluoric acid pipeline and equipment. In addition, these valves can be used in steam and seawater pipelines. Nickel valve, which has strong corrosion resistance for alkali and salt solution, is usually used in product transportation, and requires high purity working condition“ Hastelloy valve is mainly used for the pipeline and equipment for transporting strong corrosive medium such as ammonium chloride, zinc chloride, aluminum sulfate, ammonium sulfate and hydrochloric acid. Because of the complex process and expensive cost, the valve made of corrosion resistant materials should be based on enough basis to obtain the most economical value.

Structural features of high pressure lift check valve:
1. The valve disc is quenched as a whole, and can move up and down in the valve body. When the medium flows back, the valve disc will close automatically by medium pressure and spring.
2. The valve body and cover are die forgings.
3. The sealing surface on the valve seat is made of cobalt base cemented carbide plasma spray welding surface. Good wear resistance and abrasion resistance.
4. The check valve should be installed on the horizontal pipeline, and the medium flow direction is from bottom to top (positive flow).
Executive standard for check valve of high pressure power station:
1. The design, manufacture and acceptance are in accordance with ansib16.34 API6D gb12236 E101, JB / t3595 and DL / T531.
2. The structure length shall be in accordance with E101, JB / t2766, GB / t15188.1 ansib16.10 and gb12221 standards or user requirements.
3. The pressure temperature grade is according to E101, JB / t3595 API598 gb9131.
4. The size of welding groove shall be in accordance with GB 1224, JB / T 3595, ASME B16.25 and ansib16.25 standards or the piping size requirements of users.
The installation of check valve in power station should pay attention to the following matters:
1. Don't make the check valve bear the weight in the pipeline, large check valve should be supported independently, so that it is not affected by the pressure generated by the piping system.
2. During installation, pay attention to the direction of medium flow should be consistent with the direction of arrow marked on the valve body.
3. Lift type vertical disc check valve shall be installed on vertical pipeline.
4. Lift type horizontal disc check valve shall be installed on horizontal pipeline.

Flow and pressure regulating valve is also known as piston type multi-functional control valve, because it has a variety of control functions (such as water level control function, pressure reduction control function, pressure holding and pressure relief control function, flow control function, etc.), it can play the role of no cavitation, no turbulence, no vibration, anti impact, etc.
When the flow rate and pressure regulating valve is small, the valve has good energy dissipation effect on the fluid and effectively prevents cavitation; When the flow rate is large, the valve can reduce part of the fluid energy and retain part of the fluid energy to ensure that the valve has sufficient flow capacity. Its main advantages are as follows: to achieve accurate flow control, can maintain a constant flow; Realize the regulation in the range of large pressure difference, and keep the pressure behind the valve stable; Manual and electric control modes can be selected, and the electric flow and pressure regulating valve can also realize remote control, so that the operator can make high-precision adjustment as required without arriving at the site.
Under the condition of small flow, the regulating valve has good fluid energy dissipation effect on the valve and effectively prevents cavitation; When the flow rate is large, the valve can reduce the fluid energy and retain the fluid energy to ensure that the valve has enough flow energy. Its main advantages are as follows: to achieve accurate control of flow, can maintain a constant flow; Large regulation range of pressure to keep the pressure behind the valve stable; Two kinds of manual and electric control modes can be selected. The power flow and pressure regulating valve can be remotely controlled. The operator does not need to go to the site, and can make high-precision adjustment according to needs.