In a system of ventilation recently established in New York City, the fresh-air blast is produced by a Root blower, which is driven by an Otto gas engine. As there is a possibility of the flame at the engine being extinguished, the gas might escape and prove dangerous, so the arrangement herewith described was devised to insure the prompt shutting off of the gas the moment the engine stops, as it must immediately do if the jet is extinguished.

Figure 1 Is a diagram of arrangement showing the operation of the cut-off without regard to scale or precise details. In it A is the gas engine, driving the blower C from the countershaft B. D is the blast main, F is a branch hose to the collapsible bag G, H is the cut-off valve, I is the gas meter, K is the supply to the engine, and J J are equalizing bags. So long as pressure is maintained in the main D, it will be the same in F, and will keep bag G distended, thereby holding open valve H. But if the pressure ceases in D and F, bag G collapses, allowing valve H to close by a counterweight and shuts off the gas.

Figure 2 shows the operation of valve II by bag G, which rests on a shelf or table P, and supports on top a disk O pivoted to the lever L, which has a fulcrum at M and a guide at N, and raises or depresses valve stem S. When the bag G is inflated the position of the lever, etc. is as shown, but if the bag is emptied the lever L, actuated by its adjustable counterweight W, falls to position L1, and the double poppet valves fall to their seats, thus promptly shutting off the gas. When the engine is started it is only necessary to hold lever L up until the blower starts, when it will remain as shown.

AN AUTOMATIC GAS ENGINE CUT-OFF.

For a description and sketch, from which our illustrations are prepared, we are indebted to W. J. Baldwin, consulting engineer, who devised the arrangement.