EQUIPMENT AT MOUNTAIN LAKES 



117 



TEMPERATURE 



CONTROL 



UNIT- 



THERMOMETER 

 -WELL 



BACK-PRESSURE 

 GAUGE - 



SUCTION LINE 

 TO COMPRESSOR 



WATER 



TEMPERATURE 

 EXCHANGE UNIT-J 



MANOMETER 



-PROJECTOR 



-TO LTO AIR 



VACUUM COMPRESSOR 



PUMP 



WATER HEATER 



Figure 51>. Operating schematic of hydraulic arrangement for low-frequency system. 



to the venting cock at the top. When the system is 

 freshly filled, the water may be heated and circulated 

 under vacuum to decrease the amount of air in solu- 

 tion, though the chamber and instrument are care- 

 fully debubbled by hand before each test. 



Hydrostatic Pressure Chamber. Hydrostatic pres- 

 sures up to 100 pounds per square inch arc obtained 

 by the use of air from a small compressor unit. The 

 pressure is transmitted through a moulded rubber 

 bag of negligible stillness, mounted in a bronze 

 chamber. As may be seen in Figure 52, the water side 

 of the bag connects to the calibration chamber 

 through a line with high acoustic impedance. The 

 air line connects to both the pressure chamber and 

 the rear chamber of the sound source through suit- 

 able control valves, thus equalizing the pressures on 

 the sound source diaphragm. A manometer is con- 

 nected to the system in such a way that the pressure 

 differential may be checked at all times. Since there is 

 need during a hydrophone calibration to read the 

 mercury column to within ±0.1 mm, an optical sys- 

 tem was used which allows displacements of less than 

 1 cm to be read within ±0.05 mm without parallax. 



□ LIFTING MECHANISM 

 FOR TOP 



|" 0IA STEEL SHAFT 



o , l^ —SCREW-MALE 



in ^SCREW-FEMALE 



OIA STEEL BALL 



SEMI -POLISHED 

 SURFACE 



Figure 53. Calibration section of low-frequency system 

 lank, showing top lifting mechanism and major di- 

 mensions. 



