Help needed for Class IV Shutoff 1

[msmedesign]

Per ANSI/FCI70-2-1991 Class IV shut-off described as 0.01% of rated valve capacity. Test procedure A.

Valve capacity described as “the quantity of test fluid (air or water) that would pass through the valve at rated travel under the stated pressure conditions as determined by the appropriate equations and manufacturer’s ratings.

Test Procedure A:
5.1.2 Pressure of test medium shall be 3-4 bar (45-60 psig) or the maximum operating differential pressure whichever is less
My question is:
If only the cv value of the valve and the Class of the shut-off known. How I can test and know if the vavle is Class IV shutoff.
Should I test the valve with 45-60 psi water. If the seat leakage is less then 0.01%of the cv value, does it meet the standard. Or do I need to convert the cv value to "rated valve capacity", ifso how do i do that.

Thanks for your help

 

[cranekiran]

Hi,

You are right, cause I got some info. for you from a web-site,Hope It helps:-

There are actually six different seat leakage
classifications as defined by ANSI/FCI 70-2-1976. CLASS IV is also known as METAL TO METAL. It is the kind of leakage rate you can expect from a valve with a metal plug and metal seat. CLASS VI is known as a SOFT SEAT classification. SOFT SEAT VALVES are those where either the plug or seat or both are made from some kind of composition material such as Teflon.

Valve Leakage Classifications

Class I. Identical to Class II, III, and IV in construction and design intent.

Class II. Intended for double-port or balanced singe-port valves with a metal piston ring seal and metal-to-metal seats. Air or water at 45 to 60 psig is the test fluid. Allowable leakage is 0.5% of the rated full open capacity.

Class III. Intended for the same types of valves as in Class II. Allowable leakage is limited to 0.1% of rated valve capacity.

Class IV. Intended for single-port and balanced single-port valves with extra-tight piston seals and metal-to-metal seats. Leakage rate is limited to 0.01% of RATED VALVE CAPACITY.

Class V. 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.

Class VI. 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.

Since you have to test the valve at rated valve capacity then your pressure must be 45-60psig as you have yourself stated.

Bye!

 

[Scotsinst]

One thing to bear in mind is the shutoff pressure of the valve. The actuator must be sized to maintain Class IV shutoff at your specified shutoff pressure.
Ask the vendor to supply his actuator sizing calculation which should include unbalanced area times pressure drop (pressure tends to open for most control valves except Valtek Mark 1) plus packing friction plus seat load required to maintain Class IV shutoff (Fisher use 40 lbf per lineal inch of seat circumference for Class IV.

 

[GGOSCO]

In order to check the allowable leakage rate on a valve rated to have a class IV shut-of, you do currently have enough information.
Cv is quite simply the flow rate in usgpm with a 1 psig pressure drop across the valve. To calculate your allowable leakage rate, multiply the Cv value by 0.01%.

For example, if a valve has a Cv of 1000 or in other words, has a rated flow of 1000 usgpm with a 1 psig pressure drop your allowable leakage rate would be 1000 X 0.0001 = 0.1 usgpm.

This may sound like quite a bit of leakage, but remember these leakage classes are from a control valve standard. Proper piping design would call for a shut-off valve upstream of the control valve to isolate it.

http://www.ggosco.com

 

[Khusan]

please can u give me codes of ANSI and API standards
for leakage and shut off classes
please its urgent.

 

[snarayan]

msmedesign,

I believe the answer to your question is "CV=Valve rated capacity". I hope that this will clrify your doubt.

 

[gvga]

Hi,
I have just joined the site, seems really useful. I have been searching for some technical information that you may be able to assist with.
I am checking some valves bought from a supplier, they are actuated ball valves, soft and metal seated types. Our specification is for BS6755 valves with bubble tight leakage requirement. The valves are ESD service in Hydrogen purification service.
We have been offered certification quoting API 6D testing with satisfactory results. Is API 6D a standard purely for bubble tight zero leakage valves ?