Often there is confusion regarding DPE (double piston effect) seats, and DBB (double block and bleed), and we now have DIB-1 and DIB-2 in Annex B of ISO 14313/API 6D in the mix. Much of thePneumatic and electric diaphragm pumps confusion comes from the use of the word "double" and that fact that all of these terms have something to do with the seats. The ISO/API definition of DBB reads as follows: "single valve with two seating surfaces that, in the closed position, provides a Sweage pumps &Sludge pumpsseal against pressure from both ends of the valve with a means of venting/bleeding the cavity between the seating surfaces". The definition for DIB reads as follows: "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". The Multi-stage pumpsdefinition of DIB isn't very clear all by itself, so it's best to read it concurrently with the requirements of the DIB testing in Annex B for clarification. A DPE seat, is a seat design, where the Slurry pumpslocation of the seals on the back side of the seat are located in such a way that the seat can use pressure from either the pipeline or the valve cavity as a source of pressure to provide a piston force to effect a seal. Conversely, a SPE (single piston effect, or self-relieving) seat has the seals on the back side located in such a way that the Other pumpspiston force can only come from the pipeline direction. If the body cavity pressure exceeds the pipeline pressure (no more than 1,33X the valve pressure rating per ISO/API) a SPE seat will release pressure to the pipeline side. A SPE seat will release body pressure, even if it doesn't exceed the valve pressure rating, but if there is a differential pressure between the pipeline and the body cavity, where the body cavity is at a higher pressure. The amount of differential pressure at which the seat will relieve varies by valve model and manufacturer.

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