40 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



PN_176R 



Figure 72. — Evaporator house with opening in the roof 

 for venting the steam results in a steam-filled building. 



method, four walls extending from the rectan- 

 gular roof opening to within 6 feet of the floor 

 are constructed to serve as a chimney for the 

 steam. The walls are sloped so that the lower 

 edge projects 1 foot or more beyond the four 

 sides of the evaporator. The efficiency of the 

 hood is increased by attaching a strip of light- 

 weight canvas 1 to 3 feet wide to the lower edge 

 of the hood. A small gutter V2-inch deep is 

 attached to the lower inside edge of the hood to 

 collect water that condenses in it. Since the 

 hood has nothing to support, it can be made of 

 lightweight, noncorroding material such as 

 sheet aluminum. The supporting frame can be 

 made of lightweight lumber, and covered with 



aluminum on the inside so that only the metal 

 is exposed to the steam. 



This type of hood will keep the evaporator 

 house free of steam, but it has many draw- 

 backs. Being open, it requires 10 volumes of air 

 for each volume of steam removed. Thus, large 

 volumes of air must be drawn into the evapora- 

 tor house, which makes the house cold and 

 drafty. Also, the efficiency of the hood is af- 

 fected by wind and by barometric pressure. 

 Although the open hood is found in many older 

 evaporator houses, it is not recommended be- 

 cause it results in unfavorable sanitaiy condi- 

 tions. 



Tlip Covered Evaporator 



A simple, effective method for removing 

 steam from evaporators is a close-fitting, but 

 not airtight, cover from which the steam is 

 conducted to the outside of the house through a 

 duct or stack (fig. 74). The cover rests on the 

 evaporator. This method uses the same princi- 

 ple as that used to vent the steam out the spout 

 of a boiling teakettle (fig. 75). The method has 

 none of the objectional features associated with 

 earlier methods. It does not require an exhaust 

 fan and it does not raise the boiling point of the 

 sirup, since there is no measurable increase in 

 pressure within the steam-venting system. 



The cover is made of lightweight, noncorrod- 

 ing metal such as sheet aluminum and has a 



PN-4769 



Figure 73. — A canopy-type hood removes steam more 

 efficiently than do louvers. However, large volumes of 

 air are require<i to sweep the steam into and up 

 through the hood and the result is a cold, drafty 

 building. 



Figure 7U. — The tight-cover steam-venting system with 

 steam stack provides a simple, highly efficient means 

 for removing steam. This results in a steam- and draft- 

 free evaporator house. 



