Control Valve

C_v/100,000; not a drop more, and not a drop less.

--Goldilocks

yes I agree,

Thank you very much.

Why? Why not use a positive shut-off valve, such as a ball valve? If zero leakage is an essential to protect personnel, then spade-off the line under a Permit To Work system.

Thank you for the comments.

Where zero leackage is required we are using the TSO, as per recommended. Question is the value of allowable leakage for class IV valve ????

Yep. Read the original question, which has been repeated with too many question marks.

In response:

• "TSO" _{<undefined abbreviation>}?
• What does the process require?
• What is in the pipeline? Pressure? Temperature?
• What is the outome of the HazOp Study for this particular plant?

TSO is a common term used for class VI type valves and stands for "Tight Shut Off"

The concern is not the requirement of a complete valve but the calculated amount of leakage. Please see question again.

It may not be common for everyone. Good idea to avoid acronyms here. Explain and reduce the pain.

Unknown abbreviation: What is "TSO"?

TSO is a common term when we are discussing control valve and stands for,

"Tight Shut Off"

Normally it is used with class VI control valves, when describing seat tightness.

OK. So why are there now two classes of control valve in the posting, the IV and now the VI? And if the shut-off characteristics of the VI are known, why cannot the IV characteristics be found similarly? _{(Confused of Dodman's Lane)}

I will just repeat my question,

What will be the exact value of allowable leakage for a class IV valve whose rated Cv is 1070 ?

<sigh> Is there really any need to do so? _{<unsubscribes>}

YES

Well, why won't you answer PWSlack's ones?

Valve seat leakage, Class IV: 0.01% of the rated Cv value..

I hereby correct my earlier shot-in-the-dark to C_v/10,000, but up to 10 drops more or less.

--Goldilocks

According to ANSI/FCI 70-2, class IV valves must have a maximum leak rate of 0.01% of maximum capacity (flow rate), when tested with air or water at temperatures between 50 and 125º F and 45 to 60 psig pressure applied to valve inlet, with valve outlet at atmospheric pressure and closed with the normal actuator force/torque applied.

Maximum capacity is related to Cv. Calculation is easy.

Kind regards

Water as a testing medium, with an inlet pressure of 60 psi (g) and leakage is directly to atmosphere (@ 1 atmospheric pressure),allowable seat leakge for a control valve with a rated Cv of 1070 = 0.0001* 1070* SQRT(60) gallons per minute,

ie;=0.0001* 1070* SQRT(60) * 3.78541 liters per minute = 3.1374 litre/minute.

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