STEAM LOOP. The steam loop is the name given to an ingenious device, shown in Fig.
1, for returning the water of condensation from a steam pipe or separator into the boiler. It consists merely of a system of piping, and does not necessarily contain any valves, adjust ments, or moving mechanism. The following description of its method of operation is ex tracted from a lecture by Wal ter ('. Kerr before the Franklin Institute. 'rime principles on which its action depends are as follows ; Difference of pressure may be balanced by a water column ; vapors or liquids tend to flow to the point of lowest pressure ; rate of flow depends on difference of pressure and mass ; decrease of static press ure in a steam pipe or chamber is proportional to rate of con densation ; in a steam current water will be carried or swept along rapidly by friction. The water of condensation runs into a separator. (See cut.) The drip from the separator is below the boiler, and, evidently, were a pipe run from this drip outlet directly to the Wier, we would not expect the water to re turn up-hill. Moreover, the pressure in the boiler is, say, 100 lbs., while in the separator it is only 95 lbs., due to the drop of pressure in the steam pipe, by reason of which difference the steam flows to the engine. 'I b LIS the water must not only flow up-hill to the boiler, but must overcome the difference in pressure. The device to return it must perform work, and in so doing heat must be lost. The loop, therefore, may he considered as a peculiar motor doing work, the heat expended being radiation from the upper or horizontal portion. From the separator or drain leads the pipe called the "riser," which at a suitable height empties into the " horizontal." This leads to the "drop leg," connecting to the boiler any where under the water line. The "riser," horizontal." and leg" form the loop, and usually consist of pipes varying in size from if in. to 2 in., and are wholly free from valves, the loop being simply an open hole front separator to boiler. (For convenience, stop and check valves are inserted, but they take no part in the loop's action.) Suppose steam is passing, engine running, and separator collecting water. The pressure of 95 lbs. at sepa rator extends back through the loop, but in the drop leg meets a column of water which has risen from the boiler, where the pressure is 100 lbs., to a height of about 10 ft.—that is, to the hydrostatic head equivalent to the 5 lbs. difference in pressure. Thus the sys
tem is placed in equilibrium. Now, the steam in the horizontal condenses slightly, lower ing the pressure to, say, 94 lbs., and the column in drop leg rises 6 in, to balance it ; but meanwhile the riser contains a column of mixed vapor. spray, and water, which also tends to rise to supply the horizontal as its steam condenses, and, being lighter than the liquid water of the drop-leg, it rises much faster. If the contents of the riser have a specific gravity of only that of the water in the drop leg. the rise will be ten times as rapid, and when the drop leg column rises 1 ft., the riser column will lift 10 ft. By this process the riser will empty its contents into the horizontal, whence there is a free run to the drop leg and thence into the boiler. In brief, the above may be summed into the state went that a decrease of pressure in the horizontal produces similar effects on contents of riser and drop leg, but in degree inversely proportional to their densities. When the condensation in horizontal is maintained at a constant rate sufficient to give the neces sary difference in pressure, the drop leg column reaches a height corresponding to this constant difference. and rises no further. Thus the loop is in full action, and will main tain circulation so long as steam is on the system, and the difference of pressure and quantities of water are within the range for which the loop is constructed. No water should accumulate in the separator, as it is the mission of the loop to remove it before it assembles into a liquid mass. It is here that constant and vigorous action is of great practical utility. enabling the loop to act as a preventive rather than a device for removing water after it has accumulated. The separator evidently must be of such form as to give the sweep toward and through the loop better opportunity to pick up the entrained water than is afforded the current sweeping toward the engine, pump, or steam-using device. The loop action is practically independent of the distance that the source of supply is above or below the boiler, and also independent of the length of return. It is capable of handling such quantities of water as usually exist in steam systems. It is practically limited by excessive differences of pressure, and by abnormal quantities of water.
Steel : see also Alloys : Presses, Forging. and Tempering and Hardening.