What’s the best way to set up automatic purging of a dead end?
There are commercially available products such as the Hydro-Guard: http://catalog.muellercompany.com/viewdocument.ashx?i=3320&t=d and http://hydrants.com/automatic-flushing , etc. You can get them with a dechlorinator as well if that is a concern for your flushing water.
We had to take one apart one time for maintenance and the parts included a programmable irrigation solenoid valve at the heart of the operation. They use a battery operated latching-solenoid valve so that the battery lasts an entire year and doesn't require a separate power supply. If you were considering building one to your application, Rainbird has some options for a programmable valve that would open and close per your required schedule. http://www.rainbird.ca/documents/turf/ts_TBOS.pdf
the solution is to install an automatic, standalone SWITCH FLOW-type device. It can be set for specific time slots and programmed for max daily volumes. It has a 10-year battery life (based on one daily open/shut off cycle). In case of anomalies, water is cut automatically.
This unit is set up in a concrete manhole with an cast-iron plate.
Also comes with a meter to track purged volumes.