6 BULLETIN" 1067, U. S. DEPARTMENT OF AGRICULTURE. 



cycle oil engines of the semi-Diesel type have come into favor. 

 These engines employ comparatively low compression, usually from 

 125 to 250 pounds per square inch. The speed is relatively high, 

 the engines usually running 200 to 260 revolutions per minute for 

 sizes from 50 to 150 horsepower. They are generally of the horizontal 

 type, but some are of the vertical type. Ignition is by means of a 

 hot bulb or a hot plate partially cooled by water circulation. The 

 details of design differ considerably. In providing scavenging air 

 some compress into the crank case or on the front side of the power 

 piston, while others use a large piston in front of the power piston. 

 Some have governors that may be adjusted while the engine is 

 running, while others must be stopped when an adjustment of the 

 governor is to be made. Some have crossheads, others have trunk 

 pistons. Some inject water with the fuel or into the combustion 

 chamber, others do not. Lubricating oil may be recovered from some 

 of these engines, while that employed in others is useless after being 

 used once. Some owners complain of the large amount of lubricat- 

 ing oil used. 



A point worthy of note is that all engines of this type must be 

 operated well under their maximum load to avoid trouble, and this 

 is especially true of the crude-oil engines. The exhaust from engines 

 using crude oil, unless of the Diesel type, is always smoky and often 

 contains tarry matter that will foul the cylinders and eventually 

 cause trouble. Absence of valves tends to minimize this trouble, 

 but does not entirely remove it. Coke sometimes forms in the 

 exhaust pipe if a low grade of oil is used, and the pipe must occa- 

 sionally be removed and cleaned. 



For the smaller plants, two-cycle crude-oil engines are being 

 installed to the exclusion of nearly every other type. The future 

 probably will see some of the present difficulties eliminated, and 

 further use will familiarize operators with such peculiarities as 

 require close attention and care. 



ELECTRIC POWER. 



Electricity as a source of power for drainage pumping plants has 

 not come into extensive use in southern Louisiana and Texas. It has 

 the advantage of greater convenience than other sources of power, 

 and where adequate transmission lines are easily accessible this 

 advantage may make it desirable, notwithstanding its higher cost as 

 compared with power from steam or internal-combustion engines. 



TESTS OF PUMPING PLANTS. 



CONDITION OF TESTS. 



Tests of pumping plants should be made during fair weather, after 

 allowing the reservoir canals to fill to the maximum depth. If the 



