CENTRAL SCIENTIFIC CO., CHICAGO, U. S. A. 



415 



PC- 



Vertical Section. 



No. 11000. 



Horizontal Section 

 through Gears. 



No. 11002-3. 



PUMPS, CENCO-NELSON HIGH VACUUM. These pumps represent the most recent development 

 in High Vacuum Pumps for laboratory and commercial purposes. They are compact, operate with very 

 small expenditure of power, require no attention when in operation and should last indefinitely. They 

 measure about seven inches high by five inches in diameter at the base and weigh approximately ten 

 pounds. The pulley is grooved for >4-inch round belt. 



Cenco-Xelson Pumps consist essentially of rotating gears, in pairs, running in accurately fitting 

 housings. The whole mechanism is immersed in a cistern of oil, which serves the double purpose of seal- 

 ing all the joints air-tight, and of lubricating the moving parts. 



The pumps are made with either two or three pairs of gears and are known as the two-stage and 

 three-stage pumps respectively. 



The Two-stage Pump contains two pairs of gears, arranged one above the other. The upper pair 

 takes the air from the inlet tube and delivers it to the lower pair, which forces it out through the 

 exhaust. The Three-stage Pump contains three pairs of gears arranged in the same way. The Three- 

 stage Pump is capable of producing a higher vacuum than the Two-stage one. 



When operating for any length of time, these pumps will become warm. As this raises the vapor 

 tension of the oil, it is objectionable when a high vacuum is desired. To offset this effect, a cooling 

 system is provided on the Three-stage Pump by means of which the oil is kept cool by circulation of 

 water. 



The most efficient speed of operation is between 800 and 900 r. p. m. At this speed the pumps give 

 just as good results as when operated faster, and develop less heat. 



For driving these pumps, a constant speed type of motor is most satisfactory; if for D. C., a shunt 

 wound motor, or if for A. C., an induction motor. If a series wound (variable speed) motor is used, 

 the speed of the motor will decrease as the vacuum rises, and the operator has no control over the speed, 

 unless a rheostat is used in connection with the motor. A motor of % horse power should be used for 

 continuous duty. 



Under favorable conditions, a vacuum of 0.1 mm may be obtained with the Two-stage Pump. On 

 continuous service, some heating takes place, which lowers the vacuum somewhat. With the Three- 

 stage Pump, watei cooled, a vacuum of .05 mm may be obtained by using proper precautions. 



The displacement of these pumps in free air, according to tests in our laboratory, is approximately 

 285 cu. in. per minute, or 10 cu. ft. per hour, at a speed of 900 r. p. m. 



They will evacuate a flask of one liter capacity to a vacuum of 1 mm in two minutes. 



No A B 



Number of stages 2 3 



Vacuum, mm 0.1 0.05 



11000. PUMPS, CENCO-NELSON, unmounted $25.00 35.00 



11001. PUMPS, CENCO-NELSON, on hardwood base, without motor 30.00 40.00 



11002. PUMPS, CENCO-NELSON, on hardwood bast with % h. p., 110 volt A. C. Motor. 60.00 70.00 



11003. PUMPS, CENCO-NELSON, on hardwood base with %h. p., 110 volt D.C. Motor. 60.00 70.00 



