I can't tell from the picture, but I would suspect this "device" is a vacuum breaker or back flow preventer of some kind. These come in different configurations, but are required on sprinkler systems that are cross connected to a domestic water supply. If the system was not winterized (water blown out with air) this could be broken. It would be wise in my opinion for you to have a professional sprinkler service come in and check your system out and show you how to start it up, prepare it for winter, and make certain it is up to code. Unfortunately, many DIYers just connect to their water supply without proper back flow prevention. This risks your family's health and even others on the city water supply. Imagine a dog doing his business on top of a sprinkler head and then the water in the pipe siphoning back into your domestic water.