The ESRI Local Government Information Model expects blow offs to be in their wControlValve feature class, meaning they have a pressure control mechanism (are automatic, not manually operated). In our District, blow offs are manually operated for flushing. They differ from air-release valves, which are “automatic”.
From a geometric network analysis standpoint, should “blow offs” and the valve that we manually open to allow flow through the outlet be separated in the schema? For instance, for flushing sequence analysis?
Currently, the blow off “device” in the vault is represented by a single GIS asset. This includes the outlet and an integrated valve that must be manually operated. This valve is spec’d as a Ball valve in our District standards, but some old blow offs have integrated gate valves.
In order to account for the manual operation of the valve, and the automatic operation of the blow off outlet, should we migrate the current blow offs to both the wControlValve feature class as piControlValveType “Blowoff”, and to the wSystemValve feature class as ValveType “Ball”? We would likely want to flag the SystemValve as a blowoff valve, much like the Hydrant valves are currently flagged in the LGIM.
This may still cause topology errors, due to them being geometrically coincident. Could we account for this by moving every ControlValve blow off 0.1’ opposite the direction of the nearest main? Then they would always be “downstream” of the valve, would operate automatically, but would not receive flow unless the “upstream” SystemValve is opened.
Any feedback on how other water utilities are accounting for this would be appreciated.
Thank you,
Joe Bryant
GIS Specialist
Carmichael Water District