Variable Orifice Air Valve Technology
Empirical research confirms in over a decade of results conducted by several researchers on a variety of conditions, that the most critical factor that determines the creation of surge and waterhammer on closure of the large orifice of an air valve, or the prevention thereof, is the size of the orifice at that critical point before closure. This is regardless of whether the system on which the air valves are employed is a gravity fed main or pumping system as the surge and waterhammer phenomena occur during initial filling as well as during column separation and the subsequent rejoining of water columns.
However, research and extensive computer modeling also indicates that the size of the orifice has to be balanced with the conditions within the pipeline system as too small an orifice may dampen waterhammer but increase mass oscillation (surge) as well as increase filling times for a pipeline whilst too large an orifice will induce waterhammer.
The demand for an air valve design with a multi adjustable orifice to address the above has been understood as far back as the early 1980’s but no successful, practical commercially produced air valve was designed until the advent of AIRFLO Variable Orifice Air Valve Technology.
AIRFLO Recommended Air Valve Chamber Design
A typical Air Valve chamber should have the following considerations:
A well designed valve chamber is of importance and should be designed with easy access to the valve for installation and subsequent maintenance.
Good support is required in the event of the chamber settling. It is recommended that a layer of stone be placed under the pipe for drainage purposes.
When utilising concrete rings, utilise rings with a 1.5m diameter and with a concrete cast floor with a minimum of a 800mm opening for the air valve accumulator (see diagram 2)
Air valves generally constitute a small cost to the total value of a pipeline project but if incorrectly selected, sized and positioned, could result directly or indirectly into a host of pipeline destructive phenomena including surge, waterhammer, corrosion and high energy consumption. The last 20 years has seen a great amount of research on air in pipelines and the characteristics of air valves.