| July/August 1969

  • Common injector

  • Common injector

312 E. Franklin St. Crawfordsville, Indiana 47933

In response to the questions of Mr. Floyd Cook and Mr. George Pohl regarding injectors: I take pen in hand to pass information from my long association (3 years) with steam engines.

According to International Correspondence Schools (ICS) textbook of 1902 and Hawkins Maxims and Instructions for the Boiler Room of 1899, the following takes place.....

When steam is admitted into the injector, it passes the suction jet and picks up water from the supply line. The water is entrained (mixed) with the steam and a certain amount of condensation takes place. (The steam has a velocity of approximately 2500 feet per second as it enters the injector.) During the passage of the steam and water mixture through the injector the steam is condensing and until the water/steam proportion becomes correct the mixture passes out the overflow. During the condensation process, the bulk or volume of the steam may be reduced as much as 1000 times, however its velocity remains practically undiminished. While combining with the supply water, this velocity is imparted to the water. This velocity and resulting energy obtained from the steam is sufficient to cause the water to flow into the boiler.

As you can see the injector operates on a variety of laws of physics. Steam pressure, condensation and jet propulsion.

While injectors are extremely simple and will work under adverse conditions, there are certain times that they will not perform the desired function and can prove most aggravating. The water temperature cannot be too high or it will boil under the reduced pressure during pickup and cause the injector to 'slobber'. Should the overflow check valve become stuck or the seat leak, air will enter the injector and disrupt the operation. In case of too high steam pressure, complete condensation cannot take place, especially with warm water. In the case of injectors which operate with exhaust steam (not commonly used due to the presence of lubricating oil) sometimes the steam is too cold to cause the proper amount of condensation and the injector fails to function.


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