to the vessel typically at the bottom thereof a pulp outlet 14 from the vessel typically at the top thereof and a screen assembly 15 upstanding within the vessel and cooperating with the interior wall of vessel 11 to define the annular first interior volume an exemplary pressure diffuser without the gas removal means of the present invention is shown in the u s pat no 5 567 279 which is incorporated by reference pressure diffusers 10 generally have a large center chamber 20 which contains cooking liquor extracted from pulp the center chamber 20 may be a cylindrical volume extending substantially the entire vertical length of the vessel 11 the center chamber 20 contains a substantially still pool of cooking liquor extracted from the pulp slurry via the screen assembly 15 the pool allows air bubbles in the extracted liquor to rise to the top of the center chamber 20 n the pressure diffuser in some conventional pressure diffusers small vents in the top of the center chamber e g the inner head 22 allow the air to pass through the top of the center chamber into the pulp stream at the top of the diffuser and onto the next stage or blow tank in other conventional pressure diffusers air remains entrained in the cooking liquor which fills the entirety of the center chamber in these conventional diffusers the entrained air is extracted along with the liquor into the filtrate tank the entrained air necessitates larger filtrate tanks to remove the air from the liquor in.