The purpose of this Technical Information Paper (TIP) is to provide a reference basis from which paper machine vacuum system airflow requirements may be calculated. Air flow sizing requirements for fourdriniers, press sections, tissue formers and cylinder machines are presented. Considering various gap and twin wire formers which are available, it is not possible to develop a document for every former configuration.

Selection (vacuum factors) factors given in this TIP are only guidelines. Vacuum airflow and resulting vacuum levels are just part of what can influence sheet dewatering - other important factors include machine speed, forming and press fabrics, former/press configuration, roll covers, furnish (or water retention value), refining and nip impulse. Vacuum system suppliers, machine builders, or application specialists should be consulted for accurate sizing and for specific applications. Dewatering performance of formers and presses should be compared to industry standards (see TIP 0404-47 on paper machine performance) before consideration of adding vacuum capacity to meet the "TAPPI Factors." Do not only examine the existing vacuum factor compared to those in this document, but compare existing couch or press exit consistency to determine if the machine may or may not be deficient in vacuum airflow capability.

Key changes with this revision include discussions on high vacuum flatboxes with board and pulp grades where vacuum factors have been increased.