STEAM ENGINES 201 



their course through the condenser; and the condensed steam 

 leaves the condenser as fresh water, free from the Impurities 

 contained in the injection water. The water of condensation 

 from a surface condenser is therefore fit to be used as boiler 

 feed, except that it contains oil used for cylinder lubrication, 

 which can be eliminated by means of an oil separator, regardless 

 of the quality of the water used to condense it. It is for this 

 reason that the surface condenser, in spite of its greater com- 

 plication, cost, size, and weight, as compared with the jet 

 condenser, is used instead of the latter where the supply of 

 injection water is unfit for use as boiler feed. Thus, the 

 surface condenser is used altogether in marine work, except 

 for vessels navigating clean fresh water like that of the Great 

 Lakes, in order to avoid the use of sea-water in the boilers. 



In the surface condenser the steam may be outside and the 

 water inside the tubes, or the reverse. If the water is inside 

 the tubes, it should enter at the bottom of the condenser and 

 be discharged at the top. This brings the coldest v/ater into 

 contact with the partly condensed steam, and the warmest 

 water into contact with the hot entering steam. When the 

 water is outside the tubes, it is necessary to fit baffle plates 

 on the water side to force the water into a defihite and regular 

 circulation, and to prevent it from going directly from inlet 

 to outlet and also to prevent the water from arranging itself 

 in layers according to temperature, with the coldest water on 

 the bottom and the hottest water on top. The outlet should 

 be well above the top- row of tubes. A solid body of water 

 above the top row of tubes is thus assured, and the accumula- 

 tion of a stagnant body of hot water in the top of the condenser 

 is prevented by its being continually drawn off by the circu- 

 lating pump and replaced by cooler water from beneath. 



Air tends to accumulate in the top of the water side of a 

 surface condenser. This is particularly inconvenient where the 

 water is inside the tubes, as the air fills the top rows of tubes and 

 excludes the water, destroying their value as cooling surfaces. 

 To prevent this, an air valve must be provided , as high up on 

 the water side as possible, in all surface condensers, by which 

 the air can be drawn off whenever it becomes troublesome. 

 Drain valves and pipes should be provided at the bottom. 



