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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.
Also, I don't like the extra check valve before the tee or at a pressure tank etc. They hide the evidence of water underground from the well and down the well. As we semm to have now... The only check valve should be the one in or on the submersible pump's outlet or a jet pump's foot valve.