8 BULLETIN 1067, U. S. DEPARTMENT OF AGRICULTURE. 



The showing made by a pumping plant will depend to some extent 

 on the amount of vegetation in the water and consequently on the 

 time of year the test is made. A screen in the suction canal to keep 

 weeds from reaching the pump is a necessity. Even where there is a 

 good screen, weeds of small size will pass through and be caught on 

 the blades of the impeller of the pump. The effect is to reduce both 

 capacity and efficiency. There is urgent need for some form of cutter 

 that may be operated while the pump is in use. Such a device has 

 been applied to one form of screw pump. It consists of a heavy cyl- 

 inder of metal that is forced in and out by a hydraulic piston and so 

 placed that the blades of the impeller barely clear; any trash caught 

 by the blades is thus sheared off and passes on through the pump. 

 The patent involved also covers the application of the device to 

 centrifugal pumps, but so far as observation extends it has not been 

 applied to that type of pump. 



Some pumping plants are operated at an improper number of 

 revolutions per minute because of lack of data regarding the proper 

 speeds for different lifts. Without a series of tests to determine 

 the best speed of rotation a plant may be operated at considerable 

 disadvantage. Because of the limited time ordinarily devoted to 

 such a series, and the many limitations affecting the outcome of the 

 tests, it is quite probable that the results do not represent the best 

 performance of the class to which the plant belongs. 



The tests described hereafter were run by W. B. Gregory and J. M. 

 Robert, of Tulane University, and C. W. Okey, Senior Drainage En- 

 gineer, United States Department of Agriculture, assisted by B. S. 

 Nelson, Charles Kirschner, and several members of the senior class 

 in mechanical engineering at Tulane University. 



TEST OF DRAINAGE WHEEL ON THE SOUTH SIDE PLANTING CO.'S TRACT, 



NEW ORLEANS, LA. 



This test was made in 1905 on a drainage wheel used to dram 

 1,700 acres. The wheel was typical of its class, but had distinct 

 features in the double gearing and in the number of paddles. Care 

 was exercised so to design the wheel that the water would not be 

 lifted unnecessarily. Its diameter was 28 feet and its width 6 feet. 

 It was driven by a simple noncondensing engine of the slide-valve 

 type, with a cylinder 16 inches in diameter and a stroke of 24 inches. 



The method of testing consisted in traversing the discharge flume 

 with a current meter and taking indicator cards and other observa- 

 tions as quickly as possible after the traverse was finished. By this 

 means the indicated horsepower was a little less than the mean cor- 

 responding to the water measurement, but as the latter required only 

 about 10 minutes the error was not great. 



