438 REPORT OF OFFICE OF EXPERIMENT STATIONS. 



cost will be warnintod i)y the benefits received, and also one the 

 operatin«]j expense of which will be reasonable. A balance should 

 also be struck between the economical reservoir capacity and the size 

 of the pumiMii*; jilant. 



In years past a machine that has been greatly in favor, especially 

 upon the sugar plantations, is the drainage wheel. This is made of 

 any desired capacity and may vary in diameter up to perhaps 30 feet, 

 with a width of from 5 to 7 feet. By proper gearing, usually a double 

 reduction, the speed can be regulated to suit the case, but usually a 

 peripheral velocity of 3 to 4 feet per second is maintained. It is 

 probable that a speed of 5 feet is desirable, for, revolving at a greater 

 velocity, the water is liable to be carried over, while with a slower one 

 a portion of the water may flow back into the pit. These wheels are 

 placed at the end of the main ditch, and when not in operation the 

 flood gate in the levee is closed. When the circumference of the 

 wheel fits closely in a smooth pit, with the lift not exceeding one- 

 tliird the diameter of the wheel, and when running at the proper 

 speed, such a wheel will handle a large quantity of water at a small 

 cost. Although they have been made, ordinarily, by the individual 

 plantation OAvners and the actual expense of the material and labor 

 of the wheel itself is not excessive, still the large foundations required 

 make them probably more expensive than some of the more modern 

 installations. 



Another machine sometimes used is the rotary or chamber-wheel 

 pump. One objection to this form is that for the larger sizes the 

 construction necessitates that the water be lifted about 10 feet, and 

 in case the necessary lift is less than this there is lost work. They 

 are also somewhat expensive and are limited to their normal rated 

 capacities. 



The centrifugal pump is especially adapted to varying lifts, for by the 

 use of a discharge pipe whose end is submerged in the out-fall canal 

 or bayou a siphon effect is produced so that the actual head against 

 which the pump is working is simply the difference in elevation 

 between the waters in the reservoir and in the outlet canal. These 

 pumps, on account of the varying speed at which they can be oper- 

 ated, have discharges, for short periods of time, far in excess of their 

 rated capacities, which is especially desirable in cases of excessive 

 rainfalls of short duration. The ordinary type of centrifugal pump, 

 made principally of cast iron, is somewhat used and can be installed 

 with either vertical or horizontal shafts. In the latter case it can be 

 direct-connected with the steam engine. 



There is a special form of centrifugal pump particularly adapted 

 to low lifts, that has been in use for a number of years and is doing 

 most satisfactory work on a great many plantations, including three 

 of the experimental tracts. It consists of a wide, submerged im- 



