176

MODERN STEAM PRACTICE.

and packing space, thus making it perfectly water-tight. The seatin this example is cast separate, and bolted to the air-pump, andfitted with a ring of wood for the valve to beat against. The valvefitted to the top of the air-pump bücket is of a similar description,with a plain hole lined with brass, which acts as a guide. In somecases the valve on the bücket (Fig. 110) is of india rubber, workingon a grating of brass bolted to the bücket. The air-pump bücketis fitted with a junk ring and packing space, and when a brassbarrel is used may be packed with hemp, or a metallic, or evenwood packing will be found to answer. Thin metallic rings Sprunginto recesses make a first-class packing, and last much longer thanhemp.

The Ejector Condenser .—In the ejector condenser the air pump isentirely dispensed with. The principle of the apparatus may bedescribed as follows:—In every injection condenser the cold waterrushes into the vacuum with a velocity of about 43 to 44 feet persecond; while the exhaust steam from the cylinder of the engine, atthe pressure of 10 lbs. per square inch below the atmosphere, rushesinto the condenser with a velocity of about 1200 feet per second, whena vacuum of 25 inches of mercury is maintained. In the commoncondenser these rapid motions of the water and the steam are com-pletely checked, and their energy is wasted, and hence an air pump isimperative, so as to extract the water, air, and Condensed steam fromthe condenser. In the ejector condenser the exhaust steam from thecylinder of the engine after each stroke is so directed through adischarge nozzle as to unite in a jet with the condensing water, bywhich it is itself Condensed, having, however, imparted a sufücientvelocity to the combined jet to enable it to issue directly into theatmosphere in a continuous yet impulsive stream. The contentsof the condenser, both water and air, are thus ejected without theuse of an air pump, and at the same time without impairing thevacuum in the condenser. This result is obtained, however low thepressure may be to which the steam is expanded before the exhaustfrom the cylinder takes place, if the injection water be suppliedwith a few feet of head pressure: and the effect is produced bytaking advantage of the high velocity at which the exhaust steamand the injection water flow into a vacuum. The ejector condensernot only discharges the products of condensation into the atmo-sphere from a pressure of 12 lbs. per square inch below the atmo-sphere, but with a steam pressure equal to the atmosphere at the