It is, therefore, advisable to have only a shallow layer of oil in the boiler. 5. At least two single-jet pumps in series should be used. Multiple-jet pumps are not recommended because of the difficulty of regulating the flow of vapor to the various jets and of supplying the necessary amount of vapor required by them without an excessive boiler temperature. Condensed oil will bridge gaps of this narrowness m pumps of the down-jet type. Backward evaporation of the oil into the pumping line should be restrained by the use of baffles.
Cold oil is a better solvent for many gases and vapors than hot oil.
Accordingly, the condensed oil should be returned to the boiler at the maximum temperature possible. Otherwise, a certain amount of the exhaust gases and vapors dissolve in the condensed oil and contaminate it. The use of electric heat for the boiler is advisable, since it is subject to more delicate control than gas heat. A Calrod heater unit, such as used in electric stoves, can be recoiled into a helix of 2 inches in outside diameter or as a flat spiral of smaller dimensions. 13 to 18 illustrate several oil pumps which are currently popular.