Control Valve Leakage Class (ANSI FCI 70-2)

The term “Control Valve Seat Leakage Class” comes from ANSI / FCI 70-2. This is a control valve seat leakage specification Standard.

( 🔴 ) Link to FREE Udemy Course for I&C Professionals

1500+ Engineers have taken the Course
(Engineers have said it is even BETTER than the PAID Courses available)

Give it a Try 😊

Link 👉 https://asad-shaikh-instrumentation.c...


Valve Leakage Classifications

Class I – Valve Leakage Classifications Identical to Class II, III, and IV in construction and design intent, but no actual shoptest is made. Class I is also known as dust tight and can refer to metal or resilient seated valves.

Class II – Valve Leakage Classifications Intended for double port or balanced singe port valves with a metal piston ring seal and metal to metal seats.

• 0.5% leakage of full open valve capacity.

• Service dP or 50 psid (3.4 bar differential), whichever is lower at 50 to 125oF.

• Test medium air at 45 to 60 psig is the test fluid.

Typical constructions:

• Balanced, single port, single graphite piston ring, metal seat, low seat load• Balanced, double port, metal seats, high seat load

Class III – Valve Leakage Classifications Intended for the same types of valves as in Class II.

• 0.1% leakage of full open valve capacity.• Service dP or 50 psid (3.4 bar differential), whichever is lower at 50 to 125oF.

• Test medium air at 45 to 60 psig is the test fluid.

• Balanced, double port, soft seats, low seat load

• Balanced, single port, single graphite piston ring, lapped metal seats, medium load

Class IV – Valve Leakage Classifications

Intended for single port and balanced single port valves with extra tight piston seals and metal to-metal seats.

• 0.01% leakage of full open valve capacity.

• Service dP or 50 psid (3.4 bar differential), whichever is lower at 50 to 125oF.

• Test medium air at 45 to 60 psig is the test fluid.

Typical constructions:

• 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 IV is also known as metal to metal

Class V – Valve Leakage Classifications

Intended for the same types of valves as Class IV.

• The test fluid is water at 100 psig or operating pressure.

• Leakage allowed is limited to 5 x 10 ml per minute per inch of orifice diameter per psi differential.

• Service dP at 50 to 125 oF.

Typical constructions:

• 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 – Valve Leakage Classifications

Class VI is known as a soft seat classification.

Soft Seat Valves are those where the seat, shut-off disc or both are made from some kind of resilient material such as Teflon. Intended for resilient seating valves.

• The test fluid is air or nitrogen.

• Pressure is the lesser of 50 psig or operating pressure.

• The leakage limit depends on valve size and ranges from 0.15 to 6.75 ml per minute for valve sizes 1 through 8 inches.