Correct Response: C. A regulator consists of a valve that is controlled by a spring-loaded diaphragm to meter out the amount of gas necessary to maintain a preset outlet pressure that is lower than the inlet pressure. Expanders (A) and reducers (B) adapt between different diameters of lines. While they may have some effect on line pressure at very high flow rates, they are not commonly used for this purpose. A decompression valve (D) is an emergency pressure relief valve designed to avoid overpressure situations. It is not used to reduce line pressure under normal conditions.
