The objects and purposes of the inv

The objects and purposes of the invention are met by providing an energy loss detecting system for measuring the rate of flow of the vapor phase of a bi-phase fluid flow, in the presence of an unknown quantity of the liquid phase. Means separate the vapor phase from the liquid phase. Means produce a signal related to the vapor phase flow rate. Energy loss due to a faulty steam trap is measurable by interposing the vapor flow rate measuring apparatus in a steam line between a steam consuming device and the steam trap.