Mechanics of the household; a course of study devoted to domestic machinery and household mechanical appliances . f the atmosphere. Thegages used for indicating the pressure ofthe steam are made in several forms butthe type most commonly used is thatshown in Fig. 20. It is known as theBourdon type of gage and takes its namefrom the bent tube A, which furnishes itsactive principle. The Bourdon barometerinvented in 1849 employed this form ofsensitive tube. In the drawing the face ^ of the gage has been removed to show Fig. 20.—Typical Bour-the working parts. The sensitive part is f^ pressure gag
Mechanics of the household; a course of study devoted to domestic machinery and household mechanical appliances . f the atmosphere. Thegages used for indicating the pressure ofthe steam are made in several forms butthe type most commonly used is thatshown in Fig. 20. It is known as theBourdon type of gage and takes its namefrom the bent tube A, which furnishes itsactive principle. The Bourdon barometerinvented in 1849 employed this form ofsensitive tube. In the drawing the face ^ of the gage has been removed to show Fig. 20.—Typical Bour-the working parts. The sensitive part is f^ pressure gage with the ® ^ . face removed. the flat elastic tube A, which is bent in the form of a circle. When the pressure of the steam enters atS the air in the tube is compressed and the tube tends to movement of the tube caused by the steam pressure is com-municated to the pointer by a link connection and gear as shownin the drawing. The amount of straightening of the tube willbe in proportion to the steam pressure and is indicated by thenumbers marked on the face of the gage. When the pressure is. 24 MECHANICS OF THE HOUSEHOLD released, the tube returns to its original position and the spiralspring C turns the hand back to its first position. The Safety Valve.—All steam boilers should be providedwith safety valves as a safeguard against excessive steam pres-sures. Of the various types of safety valves, that known as thepop-valve is most commonly used on house-heating boilers. Itis indicated at W in Fig. 18 and is shown in section in Fig. part A is screwed into the top of the boiler at any convenientplace. The pressure of the spring C holds the valve B on its seatuntil the internal pressure reaches a certain in-tensity at which the valve is set, when it opensand allows the excess steam to escape. Whenthe pressure is reduced, the spring forces thevalve back on its seat. The handle D permitsthe valve to be lifted at any time as an assur-ance that it is in work
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