API 6A Annex F - Allowable leakage for "Ball Valve"

[danielemin]

Question 1
In the Table F.1 of API 6A annex F, there is the column with Allowable leakage usefull for some kind of valves like gate plug and check, but there isn't reference to the ball valves...
- ??? We can assume ball valves as a check valves, because the closure parts (seats and ball) rotate to close by positions, and not by "torque" like gate and plug valves???

Question 2
calculation related to the allowable leakage it is... ie. for the gate valves 30 cm3/hr/25.4 mm of nominal size..
- ??? It is right to calculate, as example, for the 5 1/8" API 10000#, bore 103.2 mm : 30 x 130.2 = 3906 cm3/hr ???
- ??? Check valve 5 1/8" API 10000# bore 130.2 mm : 5 cm3/min/25.4 mm of nominal size : 5 x 130.2 x 60 = 39060 cm3/hr

Thanks and regards.

 

[jmec87]

Answer 1:
Per the definition of plug valve in API 6A 3.1.78, a ball valve is a type of plug valve. I don't understand what you mean by "rotate to close by positions"; a ball valve is closed by torque in the same way that as a plug valve is. The API 6A definitions of plug valve and check valve are below, so you can check if your valve fits into one of these definitions:

3.1.78 plug valve
valve assembly with a plug permanently mounted across the conduit so that, when rotated 90°, it effects a closure
EXAMPLES Plugs may be straight, tapered, ball, etc.

3.1.22 check valve
valve that permits fluid to flow freely in one direction and contains a mechanism to automatically prevent flow in the other direction

Answer 2:
Note that 25.4mm = 1 inch.
So for a 5 1/8" plug (ball) valve, allowable through-bore leakage is 5.125in * 30cm3/hr/in = 153.75 cm3/hr.
For a 5 1/8" check valve, allowable through-bore leakage is 5.125in * 5cm3/hr/in = 25.625 cm3/hr.

 

[danielemin]

Answewr 1:
It' was not clear for me the definition of Ball valve like a Plug valve.
To close the "plug" you will apply torque and increasing torque you can increse the seats thightness.
In case of ball valve you can't increse thightness incresing torque. like wedge gate and in some cases also plug and globe valve.

Answer 2:
Noted for ball and pèlug.
For the check valves I think the leakage it is in cm3/min and not by cm3/hr, means = 5.125 * 5cm3/min/in = 25.625 cm3/min * 60 = 1537.5 cm3/hr , right??

Many thganks. regards.

 

[KevinNZ]

I vote that a ball valve meets the definition of a plug valve.

Ball valves can be centred so they apply constant force to the seat, or the shaft can be off centre so they force the ball into the seat as they are closed. In both cases they are rotated 90deg to seal.