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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.
The oil pressure relief valve is located at the pulley end of the engine, near the oil pump (on the right in the above schematic). When the oil is cold and thick, the resulting increased oil pressure forces the valve down against spring tension. This allows oil from the oil pump to go directly to the engine bearings.