Cast Iron Gate Valves: Gray Iron & Ductile Iron

Functions & Applications

The cast iron gate valve, furnished with cast gray iron or ductile iron body and bonnet, is a linear-motion manual valve that uses a typically flat closure element perpendicular to the process flow, which slides into the flow stream to provide shutoff. It is designed primarily for on-off services as a block valve, where the valve is operated frequently. Cast iron gate valves do not handle throttling applications well because they provide inadequate control characteristics. They are widely applied for low-pressure and ambient-temperature utility services such as water supply, sewage treatment, gas supply, district heating piping, irrigation projects, air conditioning systems, as well as food processing industry, chemical and petrochemical industry, pharmaceutical and powder industry.

Construction Characteristics

Cast iron gate valves: OS&Y rising stem (left) and non-rising stem (right); handwheel operated.

Cast iron gate valves may be optionally furnished with a series of construction characteristics:

• Outside screw & yoke (OS&Y) rising stem; non-rising stem (NRS).
• Solid wedge disc; flexible wedge disc; double disc, split wedge; double disc, parallel disc; resilient wedge (rubber encapsulated).
• Metal seated; soft seated/ resilient seated.
• End connections: RF/FF flanged; threaded.
• Operation: handwheel; gear box; electric or pneumatic actuator.

Material Selection

The body and bonnet of the cast iron gate valve shall be made of gray irons or ductile irons, which are classified according to the microstructure of graphite shape in its metallurgical pahse. The carbon that exceeds the solubility in austenite precipitates as flake (lamellar) graphite in gray iron, while that presents as tiny spheres (nodules) in ductile iron. The fracture surface of gray iron exhibits gray appearance, while that of ductile rion exhibits silver-gray appearance. Influenced by the graphite morphology, ductile iron is much stronger and has higher elongation than gray iron. However, due to the higher purity requirement on raw material and additives introduced in molten iron before casting, the cost of ductile iron is relatively higher than gray iron.

The microstructure of graphite in ductile & gray irons according to ASTM A247: Type I – spheroidal (nodular) graphite in ductile irons; Type II – flake (lamellar) graphite in gray irons.

For metal-to-metal seating surfaces, the seating materials for cast iron gate valves may be cast iron, aluminum bronze, bronze, or brass. For soft (resilient) seated cast iron gate valves, the seating materials may be rubber or plastics such as natural rubber, EPDM, NBR, PTFE, etc. The stem material shall be stainless steel, brass, or bronze. Handwheels may be made from gray iron, ductile iron, or malleable iron at manufacturer’s option. The packing materials usually are graphite and the bolting materials usually are chosen from high strength carbon steel or low alloy steel. The selection of material for each valve part shall be determined by a set of comprehensive conditions covering working pressure, working temperature, working fluids or gases, and flow rates, etc.

Design & Manufacture Standards

Cast iron gate valves may be designed and manufactured in accordance with a series of international standards:

• American Standards: MSS SP 70; MSS SP 128; API 595; API 604; AWWA C-509; AWWA C-515; AWWA C-500; AWWA C-560; ASME B16.10; ASME B16.1; ASME B16.42; ASME B1.1, B1.5, B1.8, B1.20.1, B18.2.1, B18.2.2.
• ISO & Chinese Standards: GB/T 12232; GB/T 12221; GB/T 12220; GB/T 12226; GB/T 12227; GB/T 13927; GB/T 1047/ 1048; GB/T 17241; JB/T 9092; ISO 5996; ISO 7259; ISO 5209; ISO 5752; ISO 5208; ISO 7005-2; ISO 5211; ISO 185; ISO 1083; ISO 5922.
• European Standards: BS 5150; BS 5151; BS 5163; BS 3464; EN 1171; EN 545; EN 558; EN 1092-2; EN 12266-1/ 12266-2; EN 12351; EN 12516-3; EN 12516-4; EN 1047; DIN 3352; DIN 3202; DIN 2501; DIN 3230; NF E29-324.
• Japanese & Korean Standards: JIS B2031; JIS B2062; JIS B2043; JIS B2044; JIS B2052; JIS B2002; JIS B2212; KS B2350; KS B2306; KS B1511; KS B2304.
• Common Pressure Ratings: PN10, PN16, 5K, 10K, Class 125, Class 250, Class 150, Class 300.

Supply Chain in China

Located in different industrial zones in China, there are hundreds of cast iron gate valve manufacturers that can perform massive cast-iron production. Specifically, they are located in Botou and Xintai of Hebei province, Tianjin city, Weifang and Laiwu in Shandong province, Chizhou and Wuhu in Anhui province. Shijiazhuang Metalsin Pipeline Tech Co., Ltd conducts a very strict supply chain management system, which allows us to provide quality cast iron gate valves in full spectrum with most competitive prices.