Triple off-set butterfly valve sealing in reverse direction 1

[svi]

Manufactures claim on literature that the triple off-set butterfly valves are sealing in both directions. But from experience it is known that the valve does not hold effectively against the normal flow direction. The valve standard API 609 does not address whether there is an inherent design limitation for the valve type. I would like to know user feed back on sealing, especially the larger sized valves larger than 24". Valves used for an on-off service do require to have liquid held on the other side. This may not be normal service but becomes necessary during a turn around.

 

[gerhardl]

Sealing in reverse direction is depending on construction detail, precision in manufacture, precision and correct positioning and torque for closure, sealing material and wear, and liquid type and quality.

In my experience a double or triple offset BFL valve will keep tight in both directions as promised/tested by manufacturer, under correct use.

If not up to manufacturers standard on leaking, this is usually caused by one or several of the reasons above not up to standard, not as a general rule for the valvetype.

 

[svi]

The API 609 2016 now provides more detail of the triple offset design, by way of cross sectional details. It is grouped as earlier under the category B type. It requires to be specified by the user, if the bi-directional attribute is required. It is not implicit in terms such as 'high performance', not a API 609 terminology, to provide the bi-directional sealing attribute.