FANS AND BLOWERS 



149 



taken by the U tube or by a manometer; if by a man- 

 ometer, the manometer constant should be recorded and 

 should always be used in working up the test. 



Calculation of Fan Tests by the Double Tube Method 



A fan test of this kind should be worked up in the 

 following form: 

 Fan rating 

 Motor rating 

 Double tube test, taken at r.p.m. 



Wet bulb .................. ....... deg. F. 



Dry bulb .......................... deg. F. 



/ _ 



~ 



>X39 



Effective area of pipe ............ sq. ft. 



Barometer ............. ............. in. 



Wt. of air .......................... Ib. 



Effective area of pipe= .......... sq. ft. 



The first column gives the number of the reading. 



The second and third show the impact and static 

 readings taken from the test sheet and corrected for 

 standard air. 



The fourth column shows the velocity head or the 

 difference between h f and h". 



The fifth column is friction, which must be calculated 



L X h" f 



from the velocity head by the formula "/ " = n ' 



JLJ /\ 4 / 



where "/" is the friction loss in inches of water, L the 

 length of pipe between the fan and the Pitot tube, D 

 the diameter of the pipe, if round, or the average of the 

 width and depth, if square or nearly square. L and D 

 must always be of the same denomination. The friction 

 loss should be added to both the static and impact 



