. The Locomotive. the pressurebeing equalized on both sides of the valve should there be a very smallflow. Although a new valve may close tightly it will be readily appre-ciated that leakage through the valve may develop which will surelyresult in a rise of pressure on the low pressure side should this leakagepermit a supply of steam greater than is actually required. Further-more, since any automatic device may become deranged, there is apossibility of the reducing valve ceasing to function with a consequentrise in pressure in the vessel it is supposed to protect and this rise maygo as high a
. The Locomotive. the pressurebeing equalized on both sides of the valve should there be a very smallflow. Although a new valve may close tightly it will be readily appre-ciated that leakage through the valve may develop which will surelyresult in a rise of pressure on the low pressure side should this leakagepermit a supply of steam greater than is actually required. Further-more, since any automatic device may become deranged, there is apossibility of the reducing valve ceasing to function with a consequentrise in pressure in the vessel it is supposed to protect and this rise maygo as high as the full boiler pressure. In an attempt to protect thevessel against too high a steam pressure the arrangement shown in has been used, the safety valve being set for a pressure that thevessel can carry with a reasonable factor of safety. A safety valve so applied will act as a warning signal should therebe a rise in pressure and it might, under certain conditions, protect the 38 THE LOCOMOTIVE [April, Z ^. r-300 -ZOO).SO * B o -70 -4C -30 grashoffs FORMULA W= AP, Adapted from Lipkas Graphical and Mechanical Computation. 1924] THE LOCOMOTIVE. 39 vessel. The dangerous possibilities inherent in such an arrange-ment will be seen, however, if we suppose that a small vessel requiringonly the steam that could be supplied by a 2 h. p. boiler be connectedto a steam line from a 500 h. p. installation. For real protection insuch a case the safety valve should have sufficient capacity to dischargeall the steam that could possibly flow through the supply pipe withthe full boiler pressure behind it and with the reducing valve inopera-tive. If the supply pipe should happen to be large in size it will bereadily seen that a rather large safety valve would be necessary toprevent an excessive rise in pressure. If the demand for steam at a low pressure warrants it, thenundoubtedly the safest arrangement is to have a low pressuresteam line supplied by a low pressure boiler or
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