196 



POULTRY PRODUCTION 



is usually the shortest and cheapest way out of the diffi- 

 culty, as it is almost impossible with the tools usually at 

 hand to make a crooked rod perfectly straight. 



The connecting rod is arranged so that when it is pulled 

 down by the expansion of the thermostat a thumb-nut ( H) 

 pulls on a pivot casting (G), which is situated just back of a 

 line joining the knife-edge bearings (M), which rest on the two 

 projections of the base casting {F), and which act as fulcrums. 

 The damper arm ( K) acts as a reverse lever and a little pull 

 at ( G) is transformed into a considerable raising of the damper 

 disk (i) . The damper arm is so balanced by means of the 

 counter-balance weight (J) that the damper will close of its 

 own accord unless restrained by a pull from the thermostat. 



Fig. 98 



Front and sectional views of a double hollow disk thermostat. 



This counter-balance weight is properly set by the manu- 

 facturer by means of locker nuts (0) and should under no 

 circumstances be tampered with except as a last resort in 

 attempting to secure good service from a refractory regulator. 



Thermostats. — The thermostat, which is the governing 

 mechanism of the regulating device, is usually of one of two 

 types, known as (1) bimetallic and (2) hollow disk or wafer 

 thermostats. 



The first depends upon the differing coefficients of expan- 

 sion between two metals. Such a type is shown in Fig. 97. 

 This is the most expensive type and the longest-lived. 



The second type consists of one or two hollow disks (Fig. 

 98), which are filled with one or piore volatile liquids which 



