Air Valve Offtakes
There are many different configurations and connection methods possible when making air valve connections on Polyethylene rising mains, modern Air Valves provide the following functions:
1. 'Degassing' - the continuous release of small quantities of air bubbles which are created during normal pumping operations.
2. 'Air release' - the infrequent release of large quantities of air, typically as the rising main is being filled.
3. 'Vaccum break' - allowing atmospheric air back into the pipeline when it is being drained. This prevents the pipeline from collapsing under vacuum conditions and provides efficient draining of the pipeline.
Design notes All PE pipes regardless of size, with an SDR rating of 17 or less (PN10 or more), can structurally withstand a complete vacuum (-100Kpa) without buckling. For more information on high performance Air Valves for Sewerage pumping and sizing air valves, refer to the Bayard / Talis web site or contact us for datasheets on Bayard AVUSE Sewerage air valves.
The examples below are designed help designers select the most appropriate method to make an air valve connection to a Polyethylene sewer rising main. Generally, the main considerations are:
- Air valve sizes: DN 50, 80, 100, 150*, 200* (* Uncommon)
- Air valve connection method: Threaded BSP (DN50) or Flanged (DN80-200).
- Pipe offtake method: Using an electrofusion saddle on to an existing pipe or installing an air valve tee into the pipeline.
- Connection type: Direct connection above the pipeline, Alternate connection away from the pipeline (due either to limited space constraints above the pipeline or to install multiple air valves).
Electrofusion Saddles such as the Friatec VAM top-loading saddle or Friatec SA UNI Vacuum spigot saddles are perfect for installing sewer air valves at the actual high points after the pipeline has already been installed (see a case study at HKIA here). Saddles also provide the most compact solution, minimising height from the crown of the pipe to the top of the air valve when using the direct connection method below.
Fabricated Reducing Tees are commonly used during pipeline construction. Reducing tees can be installed as a standard PE fitting in the pipeline, with a flange adaptor electrofused to the tee's off-take in order to connect the isolation valve and air valve assembly. In this case, either injection moulded reducing tee or a PE fabricated tee would be used.
Air Entrapment Tees are also commonly used in rising mains > DN350 immediately after pump stations to help capture the dissolved air, examples of these tees can be found here.
The examples below provide typical suggested connection methods and required headspace above the pipeline, depending on the air valve size, the PE pipe size and connection circumstances. For more detailed information on Air Valve connections and Air Valves email us or chat below.