FAQs: ANSI Class Flanges and Seat Leakage Classifications

A: ANSI Class Flanges are a set of standards developed by the America

A: Control valves are devices used in fluid handling systems to regulate the flow of liquids or gases. They are designed to throttle the flow, which means they control the rate of flow rather than providing a complete shut-off. The primary purpose of control valves is to maintain a specific process variable, such as pressure, temperature, or flow rate, within a desired range.

A: While control valves are not primarily designed for 100% shut-off, their ability to close tightly depends on various factors, including the type of valve and specific design features. Some control valves, such as double-seated control valves, may have poor shut-off capability compared to other types.

Q: What factors influence the shut-off capability of a control valve?

A: There are six different seat leakage classifications as defined by ANSI/FCI 70-2 1976(R1982). The most commonly used are:
1. Class IV: Also known as metal to metal, this classification involves leakage rates expected from a valve with a metal plug and metal seat.
2. Class VI: Known as a soft seat classification, it involves valves where either the plug or seat, or both, are made from composition materials such as Teflon or similar.

A: The valve leakage classifications are as follows:
1. Class I: Similar to Class II, III, and IV in construction and design intent, but no actual shop test is performed. Class I is also known as dust tight and can refer to metal or resilient-seated valves.
2. Class II: Intended for double port or balanced single port valves with a metal piston ring seal and metal-to-metal seats. It allows 0.5% leakage of full open valve capacity.
3. Class III: Intended for the same types of valves as Class II, but it allows only 0.1% leakage of full open valve capacity.
4. Class IV: Intended for single port and balanced single port valves with extra tight piston seals and metal-to-metal seats. It allows 0.01% leakage of full open valve capacity.
5. Class V: Intended for the same types of valves as Class IV. It allows leakage limited to 5 x 10 ml per minute per inch of orifice diameter per psi differential using water as the test fluid.
6. Class VI: Known as a soft seat classification, intended for resilient seating valves, and leakage limits depend on valve size, ranging from 0.15 to 6.75 ml per minute for valve sizes 1 through 8 inches, using air or nitrogen as the test fluid.

A: Class II:  Balanced, single port, single graphite piston ring, metal seat, low seat load.
 Balanced, double port, metal seats, high seat load.
Class III:  Balanced, double port, soft seats, low seat load.
Balanced, single port, single graphite piston ring, lapped metal seats, medium seat load.
Class IV:  Balanced, single port, Teflon piston ring, lapped metal seats, medium seat load.
Balanced, single port, multiple graphite piston rings, lapped metal seats.
Unbalanced, single port, lapped metal seats, medium seat load.
Class V:  Unbalanced, single port, lapped metal seats, high seat load.
Balanced, single port, Teflon piston rings, soft seats, low seat load.
Unbalanced, single port, soft metal seats, high seat load.
Class VI: Class VI is known as a soft seat classification. Specific constructions depend on resilient materials such as Teflon used for the seat or shut-off disc.

A:
– Class II and III: Test medium air at 45 to 60 psig.
– Class IV and V: Test medium air at 45 to 60 psig or water at 100 psig or operating pressure (whichever is lower).
– Class VI: Test fluid is air or nitrogen at the lesser of 50 psig or operating pressure.

A: National Standards Institute (ANSI) that specify the dimensions, materials, and pressure ratings for flanges used in various industries. These flanges are essential components in piping systems as they provide a means to connect pipes, valves, and other equipment.