Air Valve Offtakes
There are many different configurations and connection methods possible when making air valve connections on Polyethylene rising mains. Modern Triple Function Air Valves are manufactured from Polymer, are unaffected by H2S attack and provide the following three functions:
1. 'Degassing' - the continuous release of small quantities of air bubbles which are created during operation from change in pressure and pumping.
2. 'Air release' - the infrequent release of large quantities of air, typically as the rising main is being filled.
3. 'Vacuum break' - the infrequent allowance of atmospheric air back into the pipeline when it is being drained. This prevents the pipeline collapsing under vacuum conditions and provides efficient draining of the pipeline. Design note on Vacuums: All PE pipes regardless of size, with an SDR rating of 17 or less (PN10 or more), can structurally withstand a complete vacuum (-100Kpa) unsupported, without buckling.
For more information on high performance Air Valves for Sewerage pumping and sizing of air valves, refer to the Bayard / Talis web site or contact us. Data sheet for a typical Polymer Sewerage Air valve: Bayard AVUSE Sewerage air valve
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* (* these sizes are not common)
- Air valve connection method: Threaded BSP (DN50) or Flanged connection (DN80-200)
- Pipeline connection type: Direct installation onto the pipeline, or remote installation, away from the pipeline (typically due to limited space above the pipeline to ground level or due to pipeline size the need to install multiple air valves)
- Pipeline status: On an existing pipeline - fusing an electrofusion saddle to the existing pipe surface at the pipeline high points, On a new pipeline - installing an air valve tee or Air entrapment tee into the pipeline during construction.
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. 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. Saddle tees being used at HK Airport)
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. Fabricated Tee being used at HK Airport)
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, 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.
Valve Height is a significant contributor to the overall heigh of the Air Valve assembly when making a direct connection. Where there is insufficient vertical space, Knifegate valves are ¼ the face to face dimension compared to a Series 3 BSEN 1074 Gate valve.
This valve combined with EF Saddle air valve offtakes can achieve height reductions, however if there is still insufficient height, using an Air Entrapment Tee and remote mounting the air valve above ground maybe the only option available.
For alternate solutions contact us. Images courtesy of Erhard
