with a means of venting/bleeding the cavity between the seating surfaces.” The 2008 note details out this valve isn't going to supply positive double isolation when just one side is stressed. Double block & bleed valve reduce charges of set up and allow less potential paths for leakage when http://valvesandfittings18256.bloggin-ads.com/11739443/the-double-block-and-bleed-valve-diaries