PURPOSE: To provide an apparatus in which the generation of negative pressure in the low liquid level detection tube is blocked by arranging a means for detecting the low liquid level or the like with a vacuum source connected to the pipe through a control valve.
CONSTITUTION: Low liquid level detection tube 3 is inserted vertically into an oil tank of an oil tanker 1. The lower end 3' of the tube 3 is reatained at a suction bell tube 5 of an oil lifting pump 4 namely at the lowest liquid level and a detection piping 7 is arranged up to a vacuum source 13 through a throttle orifice and a changeover valve 11. The branch of the piping 7 is provided with a negative pressure detection switch 9 which provides a signal to actuate a low liquid level alarm through a detection controller 9. Also provided is a detection switch adapted to start working when the oil level of the oil storage tank reaches almost half by a level gauge 14. With the switching of the changeover valve 11, the oil tank is connected to the vacuum source 13 to perform suction. Oil is sucked up to the height h of water column equivalent to the vacuumness of the vacuum source 13 and then, the tank is sealed. As a result, the pressure in the detection piping is turned to a negative level. This actuates a negative pressure detection switch so that a low liquid level alarm 10 indicates the pressure of liquid through a detection controller 9.
KOSUGI KATSUO
INOUE KENJI
NAKAKITA SEISAKUSHO