Liquid nitrogen level controller

Claim 1

Apparatus for maintaining the level of cryogenic normally gaseous fluid which is at a liquefied temperature comprising: a. means for containing the liquid forming a free surface; b. gas thermometer means having a sealed fluid containing tube with an end extending into said container means for partial immersion in said liquid and the other end extending out of said container, the aforesaid fluid within said tube at a pressure at which said fluid within said tube is liquid at the temperature of said liquid within said containing means so that said tube contains vapor and condensed vapor of said fluid; c. solenoid valve means upon actuation for adding liquid to said container means; and d. bourdon gauge means responsive to pressure within said tube having a magnetically operated switch for initiating said valve means to add liquid to said container means when the pressure within said gas thermometer means increases to a selected value due to declining level of said liquid causing vaporization of some condensed vapor therein, said valve means terminating the addition of liquid when said pressure decreases below said selected value due to rising level of said liquid causing condensation of vapor within said tube, said bourdon gauge means having a gauge pointer with a magnet thereon to energize and deenergize said switch upon reaching or receding from the aforesaid selected value, respectively.