CI valves are industrial valves made of gray cast iron. The valve body, valve cover and other main pressure-bearing parts are formed by casting process and are widely used for fluid control of medium and low pressure and non-corrosive media (such as water, steam and oil).
1. Material and structural characteristics
Characteristics of gray cast iron
Low cost and easy processing : Gray cast iron has excellent casting performance and the cost is only 30%-50% of cast steel valves, which is suitable for mass production;
Mechanical property limitations : Low tensile strength (about 150MPa), poor impact resistance, long-term use temperature range of -20℃ to 250℃ , and brittle fracture is prone to occur beyond this range.
Typical structural design
Valve body type : Covers flange-connected gate valves, stop valves, butterfly valves and check valves to adapt to the needs of pipeline systems;
Sealing solution : Soft seals (such as rubber, PTFE) or metal hard seals are mostly used to balance economy and sealing reliability.
2. Application scenarios and limitations
Applicable scenarios
Media type: water, low-pressure steam, neutral oil and weak acid and alkaline liquid (pH 5~9);
Pressure range: nominal pressure is usually ≤PN16, and some special designs can be extended to PN25.
Prohibited conditions
High-pressure environment: such as pipeline systems ≥PN40, which can easily cause valve body cracking;
Corrosive media: strong acids (such as concentrated sulfuric acid), strong alkalis or fluids containing high concentrations of chloride ions will accelerate the corrosion of gray cast iron;
High-velocity particle fluids: sand or hard particles can easily scour the valve body and sealing surface, shortening the life of the valve.
3. Differences from other valve materials
Ductile iron (DI): Higher tensile strength (about 400MPa), improved pressure resistance, suitable for medium-pressure water supply or gas pipelines; Cast steel (CS): Withstands high temperature and high pressure (such as ≥550℃ steam), but the cost is significantly increased;
Stainless steel (SS): Excellent corrosion resistance, suitable for food, medicine or highly corrosive media, but the price is the highest.
4. Selection and maintenance points
Economic priority: Gray cast iron valves are preferred under non-harsh working conditions to reduce initial investment costs;
Avoid thermal shock: Valves need to be opened and closed slowly in steam systems to prevent sudden temperature changes from causing valve body rupture;
Anti-corrosion treatment: Surface spraying of epoxy resin or plating can extend the service life in slightly corrosive environments.
Summary: CI (gray cast iron) valves have become a common choice for low-pressure water and steam systems due to their low cost and simple processing, but their mechanical performance limitations require strict matching of working conditions to avoid failure risks.
