This paper presents the test results of a water ejector and new procedure to design it.
　A water ejector is applicable for dredging sand in deep place and also for incleasing pressure in suction pipe and preventing cavitation in a pump.
　For reclaiming land for a seacoast-industrial-area, and constructing the port facilities for it, a large amount of soil must be dredged and transported. The most important things are to dredge and transport soil efficiently and economically. Sometimes, people has to dredge the sand lying in deep place.
　The pomp dredgers have become more larger recently, and the maximum dredging depth is more than 30m below the water level. But, generally in accordance with the increase of dredging depth, the suction vacuum of the pump become more larger,and it couses wearing of a runner of dredging pomp due to cavitation and the operation has to be frequently interrupted to repair the weared runner. Therefore, the dredger pump must be operated at the lower mud content, for continious operation of it.
　The above descrived reason, the economical maximum dredging depth for ordinary dredgers, is less than about 20m below the water level. However, sand suitable for reclamation lay more than 20m below the water level. In such a case, the sand can be taken effectively and economically ejecting out it from under water by deep dredging machine with ejector at a mouth of the suction pipe, or by cutter suction dredger with vacuum reducing ejector at suction pipe. The new dredgers in this type are working some places in Japan.
　When large area is reclamed, soil must be transported longer distance, from dredging area to reclaiming area. Also, soil must be transported long distance when a new port is digged into land, and there is no place to damp the soil near the digging area. Since frictional loss is proportional to length of discharge pipe, the total frictional loss is very large and there will be pipe blocking for sedimentation of the soil, when the soil is transported through long distance by pipeline.
　In this case, it is desirable to provide a ejector at the middle of the discharge pipeline and to increase the discharging pressure inb the pipe. Then, the soil can be tranported longer distance easily. Another application of an ejector is a samprehandling pump. In this case, the ejector is no wear, no damage, and some effective at all.
　As described above, there are many applications of efectors in harbour construction works. But, no practical method to design ejector devices if available, at present. In this report, the authors intend to present the results of practical experiments with the large ejector experiment apparatus drived with flesh water and tranport the flesh water.
　This report is one of the reports in continuous series, preceded by The repart of the port and harbour research institute No.4 vol.4 'Study on the Pumping Efficiency of Jet-water Ejector.' For both experiments, reported here and in the former paper, the same apparatus was used, but in the experiment reported here, the experimental condations such as ratios of nozzle area to pipe and throttle area, vary more widely than the last time, and the diffuser has uniform pipe diameter in some length, (the former experiment was carried out without it). The water effeciency and the character of vacuum reduction in the suction pipe were studied for designing ejectors.
　It is desirable that the pump, regardless its type, is operated at the most effective operation point. But in reality, it is very difficult to calculate the characteristics curve of a volute pump or turbine pump, therefore, it is not easy to find out the most economical operation point of them. The authors proposed a new formula for ejector design, based on the results of the experiment, theoretical formula and empirical formula which have been used for the design. The new formula proposed here, coincoided well with the test results.