Should the valves of a pump be leaky on their seats, the pump will not work satisfactorily. Where the lower valve is not properly ground on the seat, the plunger sucks air from the feed-pipe, or through the joints or packing, and, at the return stroke, compresses part of the air in the pump, and forces the remainder back into the feed-pipe through the leaky valve. This process goes on after the feed is put on; the accumulated air stands like a cushion between the plunger and the water; and the pump will not go to work until the pet-cock is opened, when the air rushes out, permitting the water to flow in. Engineers having pumps that will not work till the pet-cock is opened, should have the suction-valve ground in; and they will find a decided improvement from the operation.
For slow train service, pumps perform the service of boiler-feeding fairly well; but, for fast passenger trains, a pump should not be tolerated. A pump can not be constructed for high-speed engines that will throw water regularly at high velocity of stroke.
CHAPTER XI.
INJECTORS.
Injectors have made remarkably rapid strides into public favor during the last ten years. It is a safe prediction to say, that, before the end of another decade, there will be no new pumps put upon locomotives. So long as injectors were imperfectly understood, and were used with no regularity, they retained the name of being unreliable; but, so soon as they began to be made the sole feeding-medium for locomotive boilers, they had to be worked regularly, and kept in order, which quickly made their merits recognized.
INVENTION OF THE INJECTOR.
The feed injector was invented by Henri Giffard, an eminent French scientist and æronaut. Its successful action was discovered during a series of experiments made with the view of devising light machinery that might be used to propel balloons. Although Giffard designed the most perfect balloon that was ever constructed, the injector was not used upon it; and the invention was laid aside, and almost forgotten. During the course of a sea-voyage, Giffard happened to meet Stewart of the engineering firm, Sharp, Stewart, & Co., of Manchester, England. In the course of a conversation on the feeding of boilers, Giffard remembered his injector, and mentioned its method of action. Stewart was struck with the simplicity of the device, and undertook to bring it out in England, which he shortly afterwards did, representing the interests of the inventor so long as the original patents lasted. By his advice, William Sellers & Co. of Philadelphia were given control of the American patents.
Seldom has an invention caused so much astonishment and wild speculation among mechanics, and even among scientists, as the injector did for the first few years of its use. Scientists were not long in discovering the philosophy of the injector’s action, but that knowledge spread more slowly among mechanics. It was regarded as a case of perpetual motion,—the means of doing work without power, or, as Americans expressed it, by the same means a man could raise himself by pulling on his boot-straps.