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The spring is typically located around a central shaft that is attached to the closing disk. The entire assembly is securely enclosed in a machined brass housing that contains the workings of the check valve. The check valve is generally located above the submersible pump unit by a few inches. This ensures that the long column of water remains in the well pipe. This increases the efficiency of the pump by not having to refill the length of the pipe every time the system calls for water.
A master valve is a single valve located at the water source that can shut off all the flow of water into the irrigation system. For more details see my article on master valves. On systems with a pump you will probably want to shut off the pump.. Make sure you have a really good quality spring-loaded check valve on the irrigation mainline pipe. The check valve goes someplace after the pump, but before the pressure switch. A good quality check valve is needed to keep the water from leaking backwards out of the system through the pump.