Abstract This paper gives a description of the arrangement, equipment, and instrumentation of the hydraulic-machinery laboratory at the California Institute of Technology. This laboratory was designed essentially to work with problems involving high heads, high speeds, and moderately large powers and rates of flow. The instruments and equipment permit both speed and precision in testing, an overall accuracy of 0.1 per cent being attainable. For the past two years the laboratory has been used for the study of pumping problems of the Colorado River aqueduct, a project which will have pumps totaling 350,000 hp when completed.