246 



HANDBOOK OF MECHANICAL DESIGN 



/Vapor filled bellpns 



Walerinkf 



■ Fig. 516. — Automobile cooling water temperature 

 is controlled by a self-contained bellows in the thermo- 

 stat made by the Bridgeport Brass Company. As 

 in the radiator air valve, the bellows itself is subjected 

 to the temperature to be controlled. As the tem- 

 perature of the water increases to about 140°F., the 

 valve starts to open; at approximately 180°F., free 

 flow is permitted. At intermediate temperatures, the 

 valve opening is in proportion to the temperature. 



Pressure 

 bellows. 



Pressure 

 connection 



, Rubber 

 / diaphragm 



Valve , 

 disk 



-Bellows 

 spring 



Spring 



action _ *^Q] 



screw -'' 



Fig. 517. — In a throttling type of circulating water 

 control valve made by C. J. Tagliabue Manufacturing 

 Company for use in refrigeration plants, the valve 

 opening varies with the pressure on the bellows. This 

 valve controls the rate of flow of the cooling water 

 through the condenser, a greater amount of water 

 being required when the temperature, and ■ therefore 

 the pressure, increases. The pressure in the con- 

 denser is transmitted through a pipe to the valve 

 bellows thereby adjusting the flow of cooling water. 

 The bronze bellows is protected from contact with 

 the water by a rubber diaphragm. 



Liquid out- 

 side of / Pressure spring 

 belJows ,' adjusted by dial 



Bimefai ' 

 rocker 



^ Pilot light 

 va/ve 



Throttling ' 

 gas valve 



Fig. 518. — An automatic gas-range control made 

 by the Wilcolator Company has a sealed thermostatic 

 element consisting of a bulb, capillary tube, and 

 bellows. As food is often placed near the bulb, a 

 nontoxic liquid, chlorinated diphenyl, is used in the 

 liquid expansion system. The liquid is also non- 

 inflammable and has no corrosive effect upon the 

 phosphor bronze bellows. By placing the liquid 

 outside instead of inside the beUovvs, the working 

 stresses are maximum at normal temperatures when 

 the bellows bottoms on the cup. At elevated working 

 temperatures, the expansion of the liquid compresses 

 the bellows against the action of the extended spring 

 which, in turn, is adjusted by the knob. Changes in 

 calibration caused by variations in ambient tempera- 

 ture are compensated by making the rocker arm of 

 bimetal suitable for high-temperature service. 



^Capillary tube 



Bellows 

 housing 



Bimetal- 

 blade 



~ ~ Double break 

 ^^ contacts 



Fig. 519. — For electric ranges, the Wilcolator 

 thermostat has the same bellows unit as is used on the 

 gas-type control. But, instead of a throttling action, 

 the thermostat opens and closes the electrical contacts 

 with a snap action. To obtain sufficient force for the 

 snap action, the control requires a temperature 

 difference between "on" and "off" positions. For a 

 control range frora room temperature to 550°F., the 

 differential in this device is plus or minus 10°F.; with 

 a smaller control range, the differential is propor- 

 tionately less. The snap-action switch is made of 

 beryllium copper, giving high strength, better snap 

 action, and longer life than obtainable with phosphor 

 bronze, and because of its corrosion resistance the 

 beryUium-copper blade requires no protective finish. 



