Seat Rings of small and big size ball valves 2

[Inchtain]

Hello,

I wonder if it is a common practice or a recommended way to weld the seat rings and pull them to remove the ball from top-entry ball valves?!

Is there any better alternatives?

Thanks

 

[Danlap]

Hallo,

Design philosophy of ball valve is that either ball or seat will worn out overtime (after dozens if not hundreds cycles), then it would be logical if seat(s) should be the one that can be 'easily' repaired or replaced. Smaller size and weight shall compared to ball. Thus, fully welded between seat against seat pocket best to be avoided.
Please note that ball and seat sealing area is quite delicate, thus adjustment after both are in place (inside the valve prior closing the bonnet) often required.

Top entry ball valve have limited access to retract ball and seat. some design that I've seen:
- Seat threaded (in) against seat pocket/adapter. And once ball is in place then it is threaded out until perfect sealing achieved between ball and seat. Later seat(s) are secured either with spot weld or some mechanical stopper.
Special tool to put and retract the seat is required.
- Spring(s) to pushed seat against ball. Be cautious, in the event of putting in / pulling out the ball then seat(s) need to be secured first on its position (pushed out against ball). Again special tool is required.
- Rising Stem Ball Valve (RSBV) 1.0 uses the thermal expansion method after seat being press-fitted into seat pocket. Don't know about recent RSBV seat design.
- T31 (not top entry) is to install the seat first and weld the body afterwards. (rotating) Seat has some degree of movement since it is designed to accommodate uniformity on worn out.

Might missed some details, since days of me installing/removing seats is years behind.

regards,
D

 

[Inchtain]

It was great post with a lot of information, so, thank you.

However, can you please explain more on the special tools needed to put and retract the back seats?

BR

 

[Danlap]

Like its name, it is special. I don't have the courtesy to own/share the drawing. Would requires some ingenuity and simply logic to think about it, I believe you can.
Give an example and hint: below from left to right: ball - adjusting bush (red arrow) - seat holder (blue arrow). Name can varies. without spring energized.


the one that need to be adjusted after ball is inserted or about to be retracted is the adjusting bush. there is some holes (you can see one on 12 o'clock) for hand 'tool' to rotate it counter clockwise or other way around. Most of the time, like many other design inserting/pulling, threading in/out often done by hand and only when torque is getting higher then special tool to be used.
PS: I am not in favor of above design as adjusting bush can be loosen.

Leave the rest to your imagination. browse "seat puller" or seat ring extractor.

Key is not the the tool itself but the required torque or turn or tolerance and sequence how to do it. Tool often as simple as a shaft with specific diameter of which valve repair shop might not have in the first place.

Regards,
D