FANS AND BLOWERS 



151 



The static pressure may be obtained as follows: 

 Divide the volume as figured for each opening by the 

 area of the fan outlet, thus obtaining the outlet velocity 

 V\. The corresponding velocity head can then be ob- 

 tained from the formula. The velocity head subtracted 

 from the impact pressure gives the static pressure, which 

 should be plotted as well as the impact pressure. 



These tests should be plotted with pressures in inches 

 of water, horse-power input to the fan, and efficiencies, 

 as ordinates ; and volumes as abscissae. 



The following form should be used for tabulating the 

 results of calculations: 

 Fan rating 

 Motor rating 

 Cone test taken at r.p.m. 



Wet bulb deg. F. 



Dry bulb deg. F. 



Barometer in. 



Wt. of air Ib. 



After the curves are plotted, the efficiency as given 

 by the calculations should be checked with the efficiency 

 obtained from the curves. This will correct any discrep- 

 ancy between the efficiencies as obtained from the curve 

 and as calculated. 



The Box Method 



The fan is arranged to discharge directly into a 

 box of sufficient capacity to reduce the air velocity to a 

 minimum. Cones similar to those used in the cone test 

 are attached to an opening in the side of the box at right 

 angles to the opening into which the fan discharges. 

 Readings are taken in the same manner as in the previous 

 test, and a record is also made of the box pressure by a 

 U tube connected to a pipe inserted through a hole in 

 the side of the box. This end of the pipe should be flush 



