. The steam-engine and other heat-motors . ery-valve. Raising the piston reduces the pressure in thespace between it and the foot-valve. If the condenser pressureis greater than this, the foot-valve rises and water and more orless air or vapor enters the air-pump. The air passes through thewater so that when the piston descends the former passes firstthrough the bucket-valves of the piston. The water passingthrough last serves to seal the valves and fill the clearance small modern jet condenser is shown in Fig. 18. ELEMENTARY PRINCIPLES. 27 The Bourdon Gage (Fig. 19).—This gage is use
. The steam-engine and other heat-motors . ery-valve. Raising the piston reduces the pressure in thespace between it and the foot-valve. If the condenser pressureis greater than this, the foot-valve rises and water and more orless air or vapor enters the air-pump. The air passes through thewater so that when the piston descends the former passes firstthrough the bucket-valves of the piston. The water passingthrough last serves to seal the valves and fill the clearance small modern jet condenser is shown in Fig. 18. ELEMENTARY PRINCIPLES. 27 The Bourdon Gage (Fig. 19).—This gage is used to indicatepressures. These are indicated on a marked dial by the move-ment of a hand. The latter receives its motion through amechanism which multiplies the motion of the free end of acurved elastic metal tube of flattened or elliptical long axis of this section is perpendicular to the plane of thetube. The steam or gas is admitted at the fixed end into theinterior of the elastic tube. As the pressure increases/ the. Fig. 19.—Double Spring Bourdon Gage. elliptical section becomes more round. This tends to increasethe inside arcs at right angles to the section, and as a conse-quence, the free end tends to move away from the fixed end. To measure very heavy pressure in hydraulic work, the longaxis is placed parallel to the plane of the tube or dial. Theeffect of increase of pressure is now to shorten the inner arcsand increase of pressure is followed by the movement of thefree end toward the fixed end. This gage may also be used to measure vacuum or the differ-ence between the absolute pressure in some vessel and the 28 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. absolute pressure of the atmosphere. When so used it is usualto mark it in inches of mercury rather than in pounds. Mercury Column.—Let Fig. 20 represent a U-tube, about40 inches long, open at one end, C, to the atmosphere andconnected to the condenser or other source of vacuum at D. Let it be fill
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