Apparatus and process for measuring change of liquid level in storage tanks

Claim 1

A process for measuring slow changes in the level of a liquid stored in a storage tank in an environment wherein the temperature of the liquid is prone to change during the measurement, such as measuring leakage of hydrocarbon fuel from an underground tank, the process comprising the steps of: placing a container into the storage tank in a position where the longitudinal axis of the container is substantially vertical and wherein its bottom reaches substantially to the bottom of the storage tank, the horizontal cross-sectional area of the container being constant along the vertical axis of the container, so that the volume of liquid contained in the container is a linear function of the height of the liquid level in the container; allowing the container to be in fluid communication with the storage tank whereby the height of the liquid level in the container is even with the liquid level in the storage tank, and measuring the height of the liquid level in the container, the measuring providing a first liquid level reading; shutting off fluid communication between the container and the storage tank for a fixed time period which is sufficient to allow effective measurement of leakage of liquid out of the storage tank, or into the storage tank; measuring for a second time the height of the liquid level in the container after expiration of the time period, the second measuring providing a second liquid level reading, any change between the first and second readings being due substantially exclusively to density change of the liquid caused by change of temperature of the liquid during the fixed time period, and after the step of measuring for a second time, allowing fluid communication to occur again between the storage tank and the container, whereby the height of the liquid level in the container and in the storage tank equalizes, and thereafter measuring for a third time the height of the liquid level in the container, the difference in the first and second readings providing the basis for mathematically calculating the theoretical level of the liquid in the storage tank which would have been caused solely by the change in the temperature of the liquid during the fixed time period, and the difference between the calculated theoretical level and the third reading providing the basis for finding the volume of liquid which has leaked into or out of the storage tank during the fixed time period.

Claim 9

An apparatus for measuring slow changes in the level of a liquid stored in a storage tank, comprising: a container disposed in the interior of the storage tank in a position where the longitudinal axis of the container is substantially vertical; means for opening and closing fluid communication between the storage tank and the containers; means for measuring the liquid level in the container, the means for measuring including sensing means and float means disposed within the interior of the container for providing an indication of the level of liquid in the container, the float means including a shaft fixedly mounted in the interior of the container, a damper piston being fixedly mounted to the shaft, a float cup, and flexible diaphragm means mounted to the float cup for engaging the shaft and for substantially centering the float cup about the shaft for up and down motion relative to the shaft, said up and down motion being sensed by the sensing means, and means for displaying the measured liquid levels.

Claim 10

An apparatus for measuring slow changes in the level of a liquid stored in a storage tank, comprising: a container disposed in the interior of the storage tank in a position where the longitudinal axis of the container is substantially vertical; means for opening and closing fluid communication between the storage tank and the containers; means for measuring the liquid level in the container, the means for measuring including sensing means and float means disposed within the interior of the container for providing an indication of the level of liquid in the container, the float means including a shaft fixedly mounted in the interior of the container, a damper piston being fixedly mounted to the shaft, a float cup, and flexible diaphragm means mounted to the float cup for engaging the shaft and for substantially centering the float cup about the shaft for up and down motion relative to the shaft, said up and down motion being sensed by the sensing means, and means for displaying the measured liquid levels.