Leakage in Ball valve
Leakage in Ball valve
(OP)
Hello!
I am finding leakage in ball valve,when it is in closed condition.
The Teflon seat is loaded by spring force from either end of ball(Inlet & outlet flow).
However experts opinion is at cold flow(-20 degF to +275degF)),Teflon doesnt give good sealing.
My question
1.what are the characteristics of seat(PTFE) & Ball (steel 440C) which drivers for leakage
2.How to determine leakage in between Ball & seat.
Would appreciate your inputs for my thought process
Thanks
John
I am finding leakage in ball valve,when it is in closed condition.
The Teflon seat is loaded by spring force from either end of ball(Inlet & outlet flow).
However experts opinion is at cold flow(-20 degF to +275degF)),Teflon doesnt give good sealing.
My question
1.what are the characteristics of seat(PTFE) & Ball (steel 440C) which drivers for leakage
2.How to determine leakage in between Ball & seat.
Would appreciate your inputs for my thought process
Thanks
John





RE: Leakage in Ball valve
Depends on the size of the leakage is it a liquid or gas? if it gas and it is not too excessive you can immerse the valve inside a vessel filled with aliquid such as water of alchol (EPA) (if you can not use water) and countes the bubbles or accumulate them into a glass vessel. Or use leak detector.
RE: Leakage in Ball valve
David
RE: Leakage in Ball valve
The main point is, however, that at below minus 15 -20 deg C, here down to almost minus 29 deg C, you will tend to go outside the 'normal' application for both metallic materials (House and ball etc.) and soft sealing materials.
Not that this is not relatively wide available for low temperatures, but standard products are not normally tested and approved for this temperature.
Checkpoints:
a) Are you sure the valve is supplied and guaranteed from supplier for existing, media, pressure and temperature?
b) If not: get correct valve, if yes, size and pressure class and operating conditions? Ask supplier for leakrate at this condition.
d) Leakrate acceptable?
...etc.
PTF is not a 'constant quality' supplied material, but may vary in structure. This may give different shrinkage and swelling (fluid absorbing), and aging (hardening) over time.
Is ice (water ice) or solids from fluid (abrasion on seals) an issue?
The seal itself could, as you state, of course be the problem alone, but the other points must at least be eliminated as problem sources.
RE: Leakage in Ball valve
RE: Leakage in Ball valve
Thanks to all for sharing knowledge with me.
I completely agree with Israelkk, however undulations after machining between ball & seal also drives for the leakage cause.
I am unable to correlate leakage with machining errors
between contact surfaces(Teflon seal& Spherical ball).
Is there any ways to build analytics for leakage,cuz presently working on concept design,need to ensure customer,leakage value when its is in closed condition
John
RE: Leakage in Ball valve
may I ask some more detail about what You generically call "leakage"?
How do You detect and measure that?
Are you testing with gas or liquid?
Which are the test conditions (pressure, temperature, etc.) and how do their change affects leakage? If You increase pressure, for example, does the leak rate increase too or not?
For general reference about leak testing, may be you'll find interesting to take a look at thread408-150132: "Zero Leakage" conept and EN 1779 std... within this Forum.
Thanks and Regards, 'NGL
RE: Leakage in Ball valve
Its internal leakage between Spherical ball & Teflon seal
When valve in closed condition(isolation of flow)
leakage is admissible 0.5cc/min at 70psid,fluid temperature -20degF to +275degF.
I am working on analytics(concept design) for liquid leakage not testing.
Presently working on concept design,indeed specification states above mentioned leakage admissible requirements.
thanks®ards
John