12 
BULLETIN 1373, U. S. DEPARTMENT OF AGRICULTURE 
Some contend that a vent over the elevator head is unnecessary if the 
garner is vented. Objection has been made to placing large vent 
pipes over the elevator heads because of the intimate contact of the 
grain "with humid outside air, which, it is claimed, would change the 
moisture content of the grain. However, it seems unlikely that the 
moisture content of grain can be appreciably affected during the short 
period that the grain is in contact with such air. 
Observations were made at three modern elevators having different 
installations. Air velocity readings were taken under various con- 
ditions, by inserting an anemometer in the vent duct and noting the 
direction of the air flow. The effectiveness of the installation was 
noted, and observations were made as to whether it tended to draw 
out grain, chaff, etc., on windy days. 
Elevator No. 1.— The anemometer was inserted in a 12-inch vent 
installed on the elevator head (fig. 9). Readings were taken, on a 
cold and windy day, when the elevator was not running, when it was 
running empty, and when it was lifting grain. The air velocity read- 
ings and the direction of the air flow in the vent are shown in Table 1. 
Table 1. — Head vent readings in elevator No. 1 
Velocity 
Volume 
Direction of air flow 
Conditions 
Ft. 
per min. 
797 
Cu.ft. 
per min. 
627 
373 
417 
Updraft „ 
Elevator not running. 
Elevator running empty. 
474 
do 
531 
Downdraft . . 
Elevator lifting grain. 
Elevator No. 2.- — In this plant a vent over the discharge end of the 
head (fig. 10) also served the garner. No velocity readings were 
taken because the conditions in the garner would affect the readings 
in the vent. It was observed that, when the vent was placed over 
the elevator discharge and no garner vent was used, the air flow was 
outward instead of inward while the elevator leg was lifting grain. 
A great deal of chaff and dust, escaping through the vent, was de- 
posited on the roof of the building. 
Elevator No. 3. — A 24-inch diameter vent was placed over the 
front leg and capped with a hood similar to those used for ventilating 
ocean vessels, velocity readings like those taken in elevator No. 1 
and a reading on the corresponding flow of air through the garner 
vent were taken. The results are shown in Table 2. 
Table 2. — Head vent and garner vent readings in elevator No. 3 
Elevator head vent readings 
Garner vent readings 
Velocity 
Volume 
Direction of air 
flow 
Velocity 
Volume 
Direction of air 
flow 
Conditions 
Ft. per 
min. 
66 
Cu.ft. per 
min. 
325 
0) 
545 
Out 
Ft. per 
min. 
None. 
190 
436 
Cu.ft. per 
min. 
Elevator not running. 
0) 
0) 
In., 
596 
1,370 
Out . 
Elevator running empty. 
111 
Out 
Elevator lifting grain. 
Velocity too low to be recorded. 
