The differential motion is accomplished by the device shown at the top of small cylinder.
FUEL ECONOMIZER AND FEED WATER PURIFIER.
This device, shown in [Fig. 93], is designed to utilize the waste products of combustion as they pass from the furnace to the chimney. Its use permits a high and consequently efficient temperature under the boilers and yet saves the excess of heat. It acts also as a mechanical boiler cleaner, furnishing a settling chamber for the deposit of the impurities separated by the heat which nearly equals that of the live steam in the boiler. This device adds largely to the water capacity of the boiler, frequently containing one-half the weight of the water held in the boiler itself.
It will be readily understood that the openings between the vertical tubes are ample for the chimney flue area and that the device is located between the chimney and the boiler, with the waste furnace heat passing between the tubes.
Fig. 93.
The economizer shown in [Fig. 93] consists of sections of vertical 41⁄2″ boiler tubes fitted to their top and bottom headers by taper joints. The top headers are provided with caps over each tube to permit cleaning out the sediment and remove and replace any tube that may become damaged. The several top headers are connected together at one end by lateral openings and the bottom headers are also connected as shown in cut, having hand holes opposite each bottom header to provide for cleaning out.
Mechanical scrapers are made to travel up and down each tube to keep them clear of soot. These are controlled by an automatic mechanism and driving head, as shown in [Fig. 93].
The important features about the economizer are, 1, its adaptability to any type of boiler, 2, the saving attained by utilizing that heat which has necessarily been an almost total waste, 3, the purifying of the water by means of the intense heat and slow circulation of the feed water.