What’s differences between the DIB-1 and DIB-2 seat of trunnion mounted ball valve?

DIB that is It's an abbreviation of “double isolation and bleed valve”. Single valve with two seating surfaces,each of which in the closed position,provides a seal against pressure from a single source,with a means of venting/bleeding the cavity between the seating surfaces(Note:This feature can be provided in one direction or in both directions.）”

DIB seat are divided into two types: DIB-1(both seats bi-directional) and DIB-2(one seat uni-directional and one seat bi-directional)

Today we will study the core difference between DIB-1 and DIB-2 valve seats:

1. Difference in valve seat sealing structure
DIB-1 adopts a two-way double-seat design, that is, both valve seats have dual isolation and relief functions; DIB-2 is a single-seat one-way or one-way double-seat structure, and only one valve seat realizes dual isolation and relief functions.

2. Requirements for relief valve configuration
DIB-1 must be equipped with a relief valve to achieve the pressure relief function because both seats are DPE (double piston effect) structures; DIB-2 adopts a combination of SPE (single piston effect) and DPE structure, so in theory it is not necessary to have a relief valve, but it is still recommended to install it in actual applications to ensure safety.

3. Installation direction restriction
Due to the one-way sealing characteristics of DIB-2, the medium flow direction must be strictly distinguished during installation to ensure that the SPE valve seat is located on the upstream side; DIB-1 has no such restriction and can be installed in both directions.

4. Difference in sealing principle
Both DIB-1 double seats achieve sealing through the double piston effect（DPE）, that is, the main pressure and the valve cavity pressure act together on the valve seat to press it against the ball; the SPE valve seat in DIB-2 only relies on the main pressure to achieve one-way sealing, while the DPE valve seat is sealed through the double piston effect.

5. Differences in application industries
DIB-1 is suitable for high-pressure scenarios that require bidirectional sealing, such as long-distance natural gas pipelines; DIB-2 is mostly used in unidirectional flow medium systems, such as unidirectional transmission pipelines in the petrochemical industry.

6. Comparison of structural complexity
DIB-1 has a more complex structure because both seats require independent discharge channels; DIB-2 reduces manufacturing costs by simplifying the discharge design, but requires extra attention to the installation direction

7. Pressure test method
DIB-1 requires testing the sealing of upstream and downstream valve seats separately, and monitoring leakage through the valve cavity discharge port; DIB-2 testing requires distinguishing between SPE and DPE valve seats, and only performing bidirectional testing on the DPE valve seat.

The above differences are due to the different designs of the valve seat sealing form and the discharge mechanism of the two structures. The actual selection needs to be comprehensively judged based on the medium flow direction, pressure level and safety requirements.