Uni-directional valve seats or SPE seats (also known as as Self Relieving seats) provide sealing Should the upstream pressure is greater compared to cavity stress (see Figure 1) but will leak In case the cavity stress is larger compared to upstream stress (see Figure two). From the shut position in http://metering-valve42073.diowebhost.com/22975000/how-dbb-valve-can-save-you-time-stress-and-money