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Automatic oil removal from an ammonia evaporator/low pressure vessel in a refrigeration system is disclosed. A liquid refrigerant level controller is utilized to drain the oil. The controller works under the principle of fluid thermal conductivity. Oil having lower thermal conductivity as compared t

Automatic oil removal from an ammonia evaporator/low pressure vessel in a refrigeration system is disclosed. A liquid refrigerant level controller is utilized to drain the oil. The controller works under the principle of fluid thermal conductivity. Oil having lower thermal conductivity as compared to liquid ammonia, activates the probe which in turn opens the valve to drain the oil accumulated in a trap of an evaporator or a low pressure vessel.

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What is claimed is: 1. An apparatus for removing oil in an ammonia refrigeration system, comprising: a) a vessel structured and arranged to receive ammonia and any oil circulating in the system; b) a sump located in a bottom of the vessel; c) the sump having an outlet connected to a compressor cran

What is claimed is: 1. An apparatus for removing oil in an ammonia refrigeration system, comprising: a) a vessel structured and arranged to receive ammonia and any oil circulating in the system; b) a sump located in a bottom of the vessel; c) the sump having an outlet connected to a compressor crankcase, with the outlet having a valve; d) a thermal conductivity sensor located in the sump and above the outlet, the sensor connected to and controlling the valve. 2. The apparatus of claim 1 wherein the outlet is connected to a compressor crankcase by way of an intermediate vessel. 3. The apparatus of claim 1 wherein the thermal conductivity sensor is located a distance above the outlet so that an oil-ammonia interface in the sump can move above and below the sensor. 4. A method of removing oil in an ammonia refrigeration system, comprising the steps of: a) trapping the oil and ammonia in a sump; b) at a location in the sump, sensing the thermal conductivity of fluid within the sump; c) if the thermal conductivity is low, a high level of oil in the sump is indicated, and an outlet in the sump is opened to remove oil from the sump; d) if the thermal conductivity is high, a low level of oil in the sump is indicated, and the sump outlet is closed. 5. The method of claim 4 wherein the step of sensing the thermal conductivity of fluid within the sump occurs continuously so that after the outlet is opened, the outlet is then closed when the level of oil drops in the sump.