GETTING WATER IN YER BERLER'


| November/December 1977



Giffard

Box 146, County Homes Road, Mt. Royal, New Jersey.

The injector is often thought of as a brass casting with mysterious powers that somehow propels water from the feed tank into the boiler. Often they fail to work at a very important moment and often the common remedy of the bucket of cold water dousing does little to alleviate the problem. Hauling the fire and shutting down is then the only alternative, although sometimes a pressure water hose applied to the injectors suction could save the situation, but not always.

There are many kinds of them including the inspirator which is only the same thing, except the jet is started first through the overflow before opening the discharge valve to the feed check. I think the make most associated with 'Iron-Men' is the Penberthy, though the Metro and the Sellers may come onto the scene. There were many others made by earlier companies that have long since fallen by the wayside, but their product lives, on, and often lay covered with dust perched up in the rafters of a barn. A little understanding of their 'mysterious inards' could possibly bring some of them back to work.

Our magical box was first invented by a French engineer named Henri Giffard in 1858 and it appears to have been introduced into this country by a William Sellers around 1860. In the original Giffard the steam nozzle was made to advance and retard into the combining cone and the jet was only established by fiddling with the steam valve and water valve, plus adjusting the steam nozzle to the correct depth. Sellers overcame this by his self-adjusting injector in 1876 and later the fixed nozzle type. I have no history of the Penberthy Company, but if someone has, I'm sure 'Iron-Men' would gladly print it.

Why does an injector feed water into a boiler? That is the question! (Seems I've heard that before somewhere.) Well, from an old 70-year handbook I have, may I quote: 'An injector works because the steam imparts sufficient velocity to the water to overcome the boiler pressure.' If we have a boiler running at 180 p.s.i. and we placed a thermometer inside, we would find that the steam and the surface of the water were much the same temperature, say 375 degrees F., but steam contains lots more work units and can expand many times its volume. One pound of water by weight, has far from the energy of one pound of steam because of the heat stored within. This is why our injector will not work on air pressure.

The whole secret to an injector is velocity, or feet per second of the steam. Fixing a nozzle to our previously mentioned boiler of 180 p.s.i., we would find that the speed of the steam leaving the nozzle would be around 3600 ft./sec. Now suppose we use water instead of steam at the same 180 p.s.i. we would find only a velocity, or speed, of 160 ft./sec. Divide 3600 by 160 and we get a ratio of 22 to one.