For steam service, it depend on the pipe sizes, pressures and temperatures of your application.

Currently researching LNG cryogenic service valve...Metal-seat Triple-offset Butterfly Valves (TOBV) are well-suited to LNG service. They are very inexpensive for inch of diameter.

Bubble tightness is a wide terminology which simply means zero leakage when the valve is in close position.Now if the medium is water then the valve should have zero leakage at twice the rated pressur

The standard way to calculate dynamic torque is to run a flow test and measure the torque required to rotate the valve at each position.

Triple offset valves are set up much like double-offset valves, except that the profile of the outside diameter of the vane is machined as a conic section. The cone would be projected upstream,

Double-offset valves, also known as high-performance butterfly valves, have the shaft mounted slightly offset from the pipe centerline, and the shaft is mounted behind the sealing band of the seat.

The non-offset valves are the low end of the spectrum. They are generally "rubber" lined. Typically capable of sealing to 150 psi, temp-limited by the elastomer of the seats, and the shaft seals by i