Seat leakage classes 2

[mikeg8]

Can the ANSI/FCI 70.2 (IEC 60534-4) control valve seat leakage classes be applied to ball valves? Well, OK, yes I know they can, but would a supplier/manufacturer supply/manufacture to such standards? Is there a standard specific for ball valves?

 

[gsxra]

When it comes to ball valves, yes manufactures can and will specific their leakage class as III, IV, V, etc. Some manufacturers will state they are bubble tight. You need to read there test proceedure on how they determine bubble tight thou.

Hope this helps.

 

[mikeg8]

Thanks gsxra. I suspected that they might use these standards. I have seen 'bubble tight' countless times, but in my (limited) experience, 3rd party inspectors aren't impressed by such phrases.

 

[JimCasey]

"Bubble Tight" does not come with a procedure to quantify it.

FCI 70.2 at least specified that you test on air or water at around 50 psi, and it strongly hints at how much leakage is allowed. It has no correlation to how much leakage you are going to get at operating pressure, though in any class except for class V. I think the Sierra club should pursue FCI for all the trees that have been killed in the printing of Class 1, which is absolutely and completely meaningless, exceeded in meaninglessness only by its uselessness.

MSS-SP61 is probably more appropriate for shutoff valves as is API 6D.

 

[NGiLuzzu]

mikeg8,
may be you'll find useful to consult the other posts about the issue in object within this forum:
- thread408-23297 ;
- thread408-76110 ;
- thread408-122060 ;
- thread408-135434 .

Hope this helps, 'NGL

 

[jsummerfield]

Check standards such as API STANDARD 598 Valve Inspection and Testing and find the requirement for zero bubbles per minimum specified test duration. Bubble tight is a phrase applied to isolation valves - and not to control valves.


John

 

[rsv]

As above post people get confused about class of leakage.
Control valves because there primary function is to control are often not leak tight - the class rating is so that clients can specify a control valve which has also got a tight shut off capability.
This is not the same as Isolation valves - API598 does allow metal seated isolation valves to have a small amount of leakage across the seats but, soft seated valves are to have Zero leakage when tested.

Class VI is for soft seated control valves and does not specify zero leakage

 

[BSQUAREDBUCKEYE]

Wasn't the original leakage class standard developed for globe control valves which are unbalanced? Trying to hold a plug down on a seat ring to provide tightness as the differential get higher is tough. Do the math... This is why class five allows more leakage per more inches of diameter per psiD.

A ball valve gets tighter with more differential across it.

Doesn't the standard also only go to 8"???

I can't count the number of times I've seen a 12" butterfly valve to class six tightness...

 

[jsummerfield]

For high performance butterfly valves with offset design refer to MSS SP-68. Seat leakage is covered in 5.2.2 Each valve furnished for shutoff or isolation service shall be subjected to a seat test using fluid as described in 5.1. at 1.1 times the shutoff differential pressure rating of the valve at ambient
temperature. No visible leakage through the body or the disc or past the seat shall be allowed. Test duration shall not be less than shown in Table 4. I TABLE 4. SEAT TEST DURATION - see the standard.

John

 

[greg1950]

The predominant standard for ball valve leakage is API 598. My company tests thousands of ball valves each year and other standards are rarely referenced. About once every 2-3 years someone (probably a control valve engineer) will request testing per ANSI/FCI 70.2 on ball valves.

I was a member of the API workgroup that made the latest revision to API 598. There are some important changes in the standard, so if you are working with any version prior to the current 8th edition (2004) you need to get the updated volume.

Greg Johnson
United Valve