"...In the ArcGIS API for Flex, you extend the BaseTask class. The url property on BaseTask should point at the SOE. You can then use the BaseTask's sendURLVariables method to make the request to the web service. The response is a Flex object from which you can access the different JSON objects returned in the response..."
It seems that the 10.1 GP Service doesn't really do a valve isolation. Just a trace. Do you have any suggestions on how to edit the model to do a valve isolation without having to give it barriers? An upstram and downstream trace would work if I could somehow get the model to only give me back the first valve it finds.