Gas Valves Are Used to Handle and Control The Flow of Gaseous Media

Gas valves are used to handle and control the flow of gaseous media such as liquefied petroleum and natural gas. They are made of metal or plastic and vary in terms of valve size, pressure rating, number of ports, and flow. Connection types consist of bolt flanges, clamp flanges, union connections, tube fittings, butt welds, socket welds, and internal or external threads. Gas valves are used in a variety of applications and industries. For example, some devices are used in aerospace, agricultural, automotive, commercial, construction, cryogenic, fire service, food service, or flood control applications. Others are used in the food processing, irrigation, maritime, medical, mining, or semiconductor industries. High-purity gas valves are used to handle gases such as nitrogen, argon, oxygen, and hydrogen. Specialized gas valves are also used in oil and gas production, the pulp and paper industry, and power generation. There are many types of gas valves. Angle valves admit gases at an angle and allow for maximum flow. Balancing valves maintain a consistent temperature and compensate for pressure drops. Ball valves provide tight shut-offs, but are not suitable for sanitary applications. Butterfly valves permit flow in only one direction. Block-and-bleed, blow-off, cartridge, check, and control valves are commonly available. Diaphragm valves separate the flow of gases from the closure element. Directional valves steer flow through selected passages. Diverter valves also redirect gas flow, while drain valves reduce surplus media. Gate or knife valves are linear motion valves in which a closure element slides into the flow to shut off the stream. Globe and pinch valves are other types of linear motion devices. Metering and mixing valves are used in specialized applications. Needle valves have a slender, tapered point at the end of a valve stem. Plug or stop-cock valves are designed for both on/off and throttling functions. Gas valves types include pneumatic valves, poppet valves, pressure relief valves, regulators, safety valves, and sampling valves. Compressor valves as well as servo, shut off, solenoid, spool, toggle, underwater, and vacuum relief or anti-siphon gas valves are also available. Gas valves are made from metallic elements such as aluminum and copper as well as metallic alloys such as brass, bronze, steel, cast iron, ductile iron, and stainless steel. Aluminum offers good electrical and thermal conductivity, high reflectivity, and resistance to oxidation. Copper, another metallic element, is ductile and malleable and one of the best conductors of heat and electricity. Both brass and bronze are copper alloys. Brass provides good bearing properties and low magnetic permeability. Sintered bronze can be impregnated with materials such as oil and graphite. Steel is a commercial iron that differs from cast iron both in terms of its malleability and lower carbon content. Ductile iron provides the machinability and corrosion resistance of cast iron while providing additional strength and toughness. Stainless steel is chemical and corrosion resistant and can have relatively high pressure ratings. Gas valves are made from a variety of plastics. Acetal polymers are semi-crystalline and offer excellent inherent lubricity, fatigue resistance, and chemical resistance. Polyvinyl chloride (PVC) is a widely used material with good flexibility, smooth surface, and nontoxic properties. Chlorinated polyvinyl chloride (CPC), a higher grade plastic used in water distribution systems, is suitable for high temperatures. Polytetrafluoroethylene (PTFE) is an insoluble compound that exhibits a high degree of chemical resistance and a low coefficient of friction. Polypropylene (PP) is similar to PTFE, but can be used in exposed applications because of its resistance to ultraviolet (UV) light, weathering, and ozone. Polyvinylidene fluoride (PVDF) is a fluoropolymer with better strength and lower creep than similar materials. Source: globalspec.com