Double isolation-and-bleed confuses the debate about DBB. API defines DIB being a “single valve with two seating ­surfaces, Just about every of which, in the shut posture, gives a seal from force from just one source, with a means of venting/bleeding the cavity concerning the seating surfaces.” This feature is http://mariolkhez.ezblogz.com/17567930/not-known-details-about-dbb-valve