Bonnet Design?

[cheaterbar]

I am curious as to different Bonnet Designs.( Gate valves )

There seem to be so many different schemes,some are round, some are rectangular. Have seen designs with cavernous Bonnet cavities.

Are ther guidelines in this sizing? Would not a very large Bonnet cavity add to pressure locking problems?

Thanks,

Cheaterbar

 

[gerhardl]

Normally the answer would be no to pressure problems.

If you have a bonnet cavity where existing fluid can escape freely, and not be locked in and compressed when the gate opens (like in a cylinder - and I do not believe a valve with this disadvantage exists), the only force from the fluid pressing on the valve is total exposed area of the gate construction times fluid pressure upstream (pxA upstream), less the similar pxA downstream. This pressure resultant is not dependent on the size of the cavity.

The pressure on the gate (total force) is also independent of the form of the cavity, but will increase if exposed total differential gate construction area to pressure inside the valve and bonnet cavity is increased.

You can perhaps argue that you will have more turbulence disturbance in the cavity by more extreme, fast flowing applications, but this again I presume would be dependent of internal lay-out more than size of the cavity.

Much more significant is the force resulting from the guiding and sealing construction, eg. the loosening torque / force for loosening and operating the valve starting with gate tight and fastened against the seat.

In my opinion there exists no rules for form of bonnet, out of normal standards to be fulfilled on constructional strength, and, if normed, flanged tops for motorization or actuator.

All else is a result of fabricating technology, cost and construction and normal performance considerations from the different producers.

 

[JimCasey]

Lower-pressure valves have thinner solid-wedge or flex-wedge gastes. And a lower-pressure valve can tolerate a bonnet with a flattened cross-section.

Pressure wants to expand its container to a round shape. Hence the rareness of square balloons. Higher pressure gate valves have round bonnets as the only practical way of containing the valve's internal pressure. REALLY high pressure valves have the bonnet cast with the body, and the top of the bonnet is sealed with a plug secured with wedge-shaped rings that seal more tightly with higher pressures (pressure-seal bonnet).