PRINCIPLES OF NAVAL ENGINEERING 



SCALE 



38.211KX 

 Figure 7-25. — Bourdon-tube differential 

 pressure gage. 



Although some bellows-type instruments can 

 be designed for measuring pressures up to 800 

 psig, their primary application aboard ship is 

 in the measurement of quite low pressures or 

 small pressure differentials. For example, 

 bellows elements are widely used in boiler 



HAIRSPRING 



SECTOR 



ELLOWS 



CASE 



PRESSURE 

 CONNECTION 



61.3(147B)A 

 Figure 7-26.— Simple bellows gage. 



control systems^2 because the air pressures of 

 the control systems are generally very low. 



Many differential pressure gages are of the 

 bellows type. In some designs, one pressure is 

 applied to the inside of the bellows and the other 

 pressure is applied to the outside. In other 

 designs, a differential pressure reading is ob- 

 tained by opposing two bellows in a single case. 



Bellows elements are used in various appli- 

 cations where the pressure-sensitive device 

 must be powerful enough to operate not only the 

 indicating pointer but also some type of record- 

 ing device. 



DIAPHRAGM ELASTIC ELEMENTS.-Dia- 

 phragm elastic elements are used for the 

 measurement of relatively low pressures or 



■^^Boiler control systems are discussed in chapter 11 

 of this text. 



142 



