PFA lined valves

[dragos12]

I was wondering about lining procedure of different valves.
Is there a norm or guide that you can share? I could never find one.
Beside Class 300 pfa lined valves are not common or limited to 6".
Anyone could advice why there is a size limit?

 

[mk3223]

Beside Class 300 pfa lined valves are not common or limited to 6".

It's a good question for the valve manufacturer, and possible that the market demand decides the valve size and rating to be made.

 

[Danlap]

Not a PTFE/PFA specialist, but seen some of the process by the valve manufacturer.
The limitation is due of several things based on cost, complexity of process and experience aka how many fail product over PTFE surface inspection post fabrication..
It is like making a spaghetti, if it is cooked unevenly might be prone for cracks, too porous then subject for the chemicals/sever product such as alkylation;sulphuric acid, etc. might penetrate right through the base metal (lead to external leakage), etc.
In general, I think the best practice is:
-PTFE seat on floating ball valve is limited to class 600# --> if significant pressure ‘push’ the ball against seat, then seat will be plastically deformed. Diminish the concept of zero leak soft seat
-Flat gasket -> limited by the size of the machine, hence it is easily available on much bigger size
-Diaphragm valve is limited to DN 200 class 300# -> PTFE diaphragm is pinched by the spindle against valve bottom, hence the bigger the area it would born more stress prone for shear shall in fully close position.
-Inner replaceable sleeve for butterfly valve -> relatively simple and standardized design, hence available in bigger sizes
-PTFE lined Plug and Ball valves -> valve body along the liner need to be put inside the oven, hence limiter is the oven size. And sometimes some machining is required post heating, so this is also limiter as machining contour inside the valve is quite complex

And maybe demand of PTFE lined ball and plug valve is not common for sizes bigger than 6” or 8”, hence manufacturer never really invest on necessary equipment. Once asked Flowserve for 12” atomac ball, says can do it, but extraordinary effort which was reflected on significant price made us back out.
Just my two cents, maybe other have better insight.

Kind regards,