liquid Nitrogen level Filler Control V. E. Schupbach, Goodyear Atomic Corp., Portsmouth,
Ohio EXHAUST PORT
o m of automatically V controllingm mliquid levels are known. ARIOUS
Many of them require fairly intricate sensing devices and flow control equipment. J'ery few, if any, of these devices can be used for controlling the level of liquid nitrogen in various systems. This article describes a device which mas developed to control the filling of mass spectrometer cold trap Dewar vessels automatically from liquid nitrogen storage Dewars, independenb of any other system. The device, whose main component is an inverted Hoke H G P valve, is very simple and remarkably efficient. A sketch of the device is shown in Figure 1; a schematic diagram of the relationship of the controller to the storage and cold trap equipment is shown in the insert, The operation of the controller depends on the temperature, and consequently the pressure, of a 2-gram propane charge in the sensing element. The lower end of the sensing element, which is made of metal tubing, is immersed in the liquid nitrogen in the cold trap Dewar. When the liquid nitrogen level falls too low (about inch below the tube), the tube of the sensing element becomes relatively warm and the vapor pressure of the propane charge increases; the increased pressure on the bellows seats the yalve and closes the vent port at about 30 p s i When the vent valve is closed the nitrogen vapor pressure gradually increases within the storage Dewar. forcing the liquid nitrogen to rise in the insulated feed line and s l o d y filling the cold trap Dewar. The pressure of the propane within the sensing element decreases upon cooling; after the liquid
1536
ANALYTICAL CHEMISTRY
LV E
COmROLLER
STORAGE
\"
SENSING
/
ELEMENT
PROPANE COLD TRAP DEWAR
Figure 1.
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Automatic liquid nitrogen level filler control
nitrogen has reached the desired level the controller valve opens and flow into the cold trap Dewar stops. No further control action occurs until the sensing element responds to a significant drop in liquid nitrogen level. I n addition to liquid nitrogen or liquid air coolant systems, this device might even find use in some chemical processes. A potential use would be a process which requires reactions to be
carried out in media such as liquid ammonia. With this controller the liquid level could be maintained at any required level. Such a change in an application might require a modification of the materials of construction and also would necessitate the selection of a suitable charge material. WORK performed under Contract AT(33-2)-1 v,-ith the United States Atomic Energy Commission.
