Slip-tube gauge

The liquid levels of products that have a Reid vapor pressure of 40 lb or more are generally determined by the use of gauge glasses, rotary or slip-tube gauges, tapes and bobs through pressure locks, or other types of gauging equipment. The type of gauging equipment depends on the size and type of the pressure tank. 

All containers, except those filled by weight, must be equipped with gauging devices to indicate the maximum permitted liquid level. Permitted types for ammonia are the rotary tube, adjustable slip tube, and fixed-length dip tube. If other gauging devices are installed, they must not be used as primary controls for filling cargo tanks. See 49 CFR 173.315(h) and 178.337-14 [9]. 

All containers, except those filled by weight, must be equipped with gauging devices to indicate the maximum permitted liquid level. Permitted types for ammonia are the rotary tube, adjustable slip tube, and... 

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