Floater ball valve

[rak29]

we have floater valves with all different sizes from 2'' to 10'',different classes from 150 to 2500.
now the body-cap material is casting WCB or LCC.
we have a problem since long time.
we found lots of valves leak during Low pressure testing.
almost all leaks are from body-cap joint.
how i can check compression for gasket.
because i doubted that leaks is due to either gasket improper compression or stud tight .

 

[DRE111]

I'd call the valve manufacturer since you don't know the design compression for the gasket and that makes it difficult for you to assess whether it's correct or not. Properly tightened body joints should be designed to handle loads transmitted by the piping, pressure, and vibration and so they should not leak.

 

[gerhardl]

Float valves? Sketch for exact type and construction and a bit more explanation on operating conditions?

I take it lower pressures are lower overpressure and not vacuum?

Does the leakage stop at higher pressures?

Preliminary, possible causes:

a) The gasket between body and cap must be changed when the valve is parted, and be of correct type and material for temperature and fluid. Extra gasket paste?

b) If better sealing at higher pressures, this is in some cases natural, fluid filling gaps and pressing/floating/expanding gasket to better thightening. This might overstress the gasket and shorten gasket life.

c) Check that sealing areas are even, without machining faults, impurities, or broken.

d) For some caps on some valves the bolt number and distribution is insufficient (weak construction) in such a way that the cap flange is drawn nearer the body flange near the bolts, and the flanges are further apart midway between bolts. Trying to tighten the flange bolts more will worsen the problem.