火电机组四大管道设计中，选用弯管或弯头时首要考虑的因素是阻力大小。从对引起争议和困惑的源头——美国Crane手册的解读着手，澄清了弯管或弯头阻力计算方法中的一些问题，并通过实例比较证实，以弯管替代弯头时，降阻节能效益十分明显，对于降低工程造价也会带来可观成效，值得在四大管道设计中推广应用。根据对Crane阻力系数规范的取用法则还得知，在理论上四大管道设计中存在着潜在的节能降阻空间。

The primary sensitive factor that the thermal power units consider in four pipes design is the resistance by using bend or elbow. The divergence existing in resistance calculation of bend and elbow is clarified according to the U.S.Crane Co. manual which is the source of disputation and perplexity. It is demonstrated by comparisons that energy saving and resistance reducing are very obvious and the project cost is reduced by replacing elbow with bend, worthy of popularization in four pipes design. It is also shown from the access rules of resistance coefficient based on the Crane regulations that energy saving and resistance reducing exist theoretically in designing four pipes.