4.12.715 LIQUID LEVEL GAUGING DEVICES
(1) Each container, except containers filled by weight, shall be equipped with a liquid level gauging device of approved design.
(2) All gauging devices shall be arranged so that the maximum liquid level to which the container may be filled is readily determined.
(3) Gauging devices that require bleeding of the product to the atmosphere, such as the rotary tube, fixed tube and slip tube, shall be so designed that the bleed valve maximum opening is not larger than a No. 54 drill size, unless the device is equipped with an excess flow valve.
(4) Gauging devices shall have a design working pressure at least equal to the design pressure of the storage tank on which they are used.
(5) Fixed liquid level gauges shall be so designed that the maximum volume of the container filled by liquid shall not exceed 85 percent of its water capacity. The coupling into which the fixed liquid level gauge is threaded must be placed at the 85 percent level of the container. If located elsewhere, the dip tube of this gauge must be installed in such a manner that it cannot be readily removed. This does not apply to refrigerated storage of anhydrous ammonia.