Positive Air Pressure Attenuation Device for Building Drainage Systems

John Swaffield (Inventor), David Campbell (Inventor)

Research output: Patent


This invention relates to a positive air pressure attenuation device for relieving positive pressure transients in drainage systems.

In such drainage systems, an air admittance valve is required to prevent the release of foul air, and to admit air under conditions of reduced pressure in the discharge pipes and stacks. Such a valve is described in EP 0278746. However, the use of these valves can prevent positive air pressure transients arising within the drainage system from escaping to the atmosphere leading to a reduced performance of the drainage system.

According to the present invention, there is provided a pressure relief device for use in a drainage system comprising a housing to which a flexible reservoir is secured, the flexible reservoir being operable on a positive air pressure transient within drainage system, and both the housing and the flexible reservoir are contained within an external casing.

Preferably, the housing has an inlet and an outlet, the inlet being connected to the drainage system, and the outlet is connected to a cap to enable sealing of the housing. The housing is fabricated from a rigid material to ensure adequate sealing of the complete unit. The housing is a continuous unit over which the flexible reservoir is fitted. Where the flexible reservoir covers the housing, means for ventilation are used to allow air in the drainage system to pass freely to and from the reservoir. A suitable material for the housing would be PVC, for example.
Original languageEnglish
Patent numberGB0121561.5 / USSN11/077.460
Publication statusPublished - 6 Sept 2001


  • positive air pressure
  • building drainage
  • attenuation


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