36 THE POLK SYSTEM 



The Polk Silo Doors 



THUS far in our discussion of silo construction, no mention has 

 been made of doors, openings for which must be left in the 

 walls. The cut below is an outside view of our door closed and 

 sealed. 



The openings which receive the doors are 20x30 inches. They 

 are usually spaced 30 inches apart but the number and location of 



Polk System Silo Door 



doors are optional with the builders. We have chosen the oval 

 shape in order to avoid sharp angles which invariably cause air 

 cracks both in the jamb and in closing the doors when filling. 

 We use a sheet steel door form, set between the shells of the ma- 

 chine as the work progresses. This form molds a concrete jamb 

 one inch wide and one-half inch in depth from the inner surface 



"They are not built of pieces and they 

 cannot go to pieces. 



