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.

TRYING TO FIND OUT HOW THE INJECTOR WORKED.

Among the mechanics I associated with, the injector was spoken of as a machine having a secret method of action. There was supposed to be some part inside, where a vacuum was formed, which sent the water into the boiler. We were all familiar with the vacuum of condensing engines, and it was a convenient solution of the mystery. I remember committing what we regarded as a heinous sin, in trying to find out the secret of the injector. On a Sunday forenoon in a Scotch town, where it was considered next to a crime to miss going to church, three of us stole quietly into an engine-house, and took an injector apart, when we knew the foreman, like a pious man, was listening to the sermon. All our plans had been laid the previous day, and the necessary tools laid conveniently at hand. The feeling of disappointment we experienced at finding nothing to explain the working of the thing, is still vivid in my memory.

THE PRINCIPLE OF THE INJECTOR’S ACTION.

The principle of the injector’s action is that of induced currents, which is much more popularly understood to-day than it was twenty-five years ago. A current of any kind has a tendency to induce a movement in the same direction of any body it passes over or touches. Thus, we are all familiar with the fact that a current of air called wind, passing over the surface of a body of water, sets waves in motion, and dashes the water high up on the shore above its original level. In the same way, a jet of steam moving very rapidly, when injected into a body of water under favorable conditions, imparts a portion of its motion, and starts momentum sufficient to overcome the original pressure of the steam. That is how the injector is made to force water into a boiler against the same pressure the steam is starting from. The principle is now utilized in the arts for many useful purposes. The ordinary locomotive blast, blowers, steam siphons, steam-jets, jet exhausters, and argand burners, are common instances of its application.

When the action of the injector is closely examined, its mystery as a source of power disappears; for it is found that an amount of heat equal to the mechanical equivalent of work done, is used up during the operation of feeding. Thus, when a given quantity of heat units pass from the throttle to work the injector, the whole of the heat does not return to the boiler along with the feed-water, as was first supposed to be the case; but a portion of heat representing the foot pounds of work done is dissipated, besides other losses incident to leakage, radiation, and convection.

DIFFERENT FORMS OF INJECTOR.

There are a great many different forms of injectors in use, but all of them conform to certain elementary principles in their mode of action. Steam passes from the boiler through the steam-pipe and receiving-tube A (Fig.1) at a high velocity, and, combining with the water at the point B, condenses, but imparts considerable momentum to the water, which rushes along into the delivery pipe, raises the check-valve, and passes into the boiler.

The tubes of the injector are arranged so that a concentrated jet of steam shall impinge upon the water to force it through passages that are designed in the best form for maintaining the solidity of the current. The speed imparted to the water represents the work performed by the steam, and upon this velocity depends the successful action of the injector. As the current of water for starting the injector could not be induced against the constant pressure on the check-valve, which equals the pressure at the throttle, an overflow is provided where the water can flow unchecked till the necessary momentum is obtained, when the overflow is closed. All deviations in construction from the elementary injector shown in Fig.1 are made for the purpose of extending the action of the injector under varied conditions, for making it work automatically under different pressures of steam, and for improving its capacity to lift water above its natural level.

A HEATER-PIPE ACTING AS AN INJECTOR.

Before the invention of the injector, cases occasionally happened of the heater-pipe acting as an injector. Where the end of the heater pipe was carried through the feed-pipe, and pointed towards the check-valve, starting the heater under favorable conditions would carry the water into the boiler. A great many old engineers relate instances where this has happened.

SKILL AND REFLECTION NEEDED IN REPAIRING INJECTORS.

Injectors can be kept in good order with less work than is needed to keep a pump going, but the highest kind of mechanical skill is required for the injector when repairs must be done. Almost any kind of machinist can fit a new chamber or plunger into a pump. Many men who will do this job satisfactorily will get badly left when they try to put a defective injector in order. To do such work, thoughtful reflection is called for, besides the hand that can do accurate fitting. A workman who may be good on guides or cross-heads or links, takes an injector apart that will not work, and can perceive nothing wrong with it, because he has not got the philosophy of the thing through his head; and he must have that before he can have insight into the probable cause of derangement.

CARE OF INJECTORS.

When an engineer finds that an injector refuses to work, his first resort should be the strainer. That gets choked with cinders or other impurities so frequently, that no time should be lost in examining it. One day, when I was running a round-house, an engineer came in breathless, with the information that his engine was blocked in the yard, and he must dump his fire, as he could not get his injector to work. The thermometer stood at twenty degrees below zero, and an Iowa blizzard was blowing; so the prospect of a dead engine in the yard meant some distressingly cold labor. I asked, the first thing, if he had tried the strainer; and his answer was, that the strainer was all right, for the injector primed satisfactorily, but broke every time he put on a head of steam. I went out to the engine, and had the engineer try to work the injector. By watching the overflow stream, I easily perceived that the injector was not getting enough water, although it primed. An examination showed that the strainer was full of cinders, and the injector went to work all right when the obstruction to the water was removed.

THE MOST COMMON CAUSES OF DERANGEMENT.

Sand and cinders are the greatest cause of failures with injectors; as they are, indeed, with all water-feeding apparatus. I knew a case where water for a locomotive, running on a short branch, was taken out of a sandy creek with a siphon. The tank had generally about six inches of sand in the bottom. The engine had a pump and an injector; but all the feeding had to be done by the latter, for the pump never worked a gallon of water. The injector worked the water through when it seemed a quarter sand. In a short time the sand destroyed the tubes of the injector, for it acted on them the same way as a sand-blast does in cutting files or glass.

A very common cause of failure of injectors, is leakage of steam through throttle-valve or check-valve, keeping the injector so hot that no vacuum can be formed to make it prime. A great many injector-checks have been turned out too light for ordinary service, while others are made in a shape that will always leave the valve away from the seat when they stop working. Then the engineer has to run forward, and pound the check with a hammer to keep the steam from blowing back; and that soon ruins the casting. Check-valves set in a horizontal position are worthless with water that contains grit.

HOW TO KEEP AN INJECTOR IN GOOD ORDER.

To preserve a good working injector, the engineer should see that all the pipes and joints are kept perfectly tight. It is hard to keep pipes and joints tight when they are subjected to the continual jars a locomotive must stand; but injectors can not be depended on where there is a possibility of air mixing with the water. Leaky joints or pipes are particularly troublesome to lifting injectors; for air passes in, and keeps the steam-jet from forming a vacuum. At first the injector will merely be difficult to start; but, as the leaks get worse, there will be no starting it at all. Then, the air mixing with the water is detrimental to the working of all injectors, as its tendency is to decrease the speed of the water. The compact molecules of water form a cohesive body, which the steam can strike upon with telling force to keep it in motion. When the water is mixed with air, it lacks the element of compactness; and the steam-jet strikes a semi-elastic body, which does not receive momentum readily. This mixture of steam and air does not act solidly on the check-valve, but makes the water pass in with a bubbling sound, as if the valve were moving up and down; and the stream of water breaks very readily when it is working in this way.

CURIOUS CASES OF TROUBLE WITH AN INJECTOR.

I ran a Sellers improved injector on a locomotive about a year, and it was an excellent feeding apparatus; but I several times had curious cases of trouble in getting it to work. Once it began drawing air; and I could not find out where the air was coming from, for the pipes seemed all tight. But the air was going through, for I could hear its mutterings; and the water kept breaking, which was an annoyance on the road. A heater-pipe was attached to the injector feed-pipe; and I afterward found out that the air was getting in at the top joint of this pipe, which did not show a leak, being above the water.

Another time I had almost a failure with this injector out in the snow. I was out with a snow-plow, opening the road through enormously deep snow-drifts. We had worked on one bank for several days; and we made water by shoveling snow into the tank, which was melted by blowing steam through the heaters and injector. Cinders were passed into the tank very freely with the snow, and presently I began to have trouble with my injector. I took it apart several times, and cleaned out cinders, when it went to work all right again. But a time came when it refused to work when there were no cinders inside, and it seemed that no amount of coaxing would make it start. It would prime all right; but, so soon as I gave it steam, the water would break. Driven to my wits’ end, I made the fireman try to work the injector, while I went down and watched its action. Everything seemed tight: I had examined the strainer, and there appeared no reason why it should not operate as well as it ever did. While watching it, I saw a drop of water oozing out at the stem of the overflow-valve; but I reasoned, “That can not affect the working of the injector, because it is ahead of where the water starts.” But, seeing that the thing would persist in not working, I put a bit of packing in the overflow-stem, thinking it will do no harm any way; and then the injector went to work all right, and I had no more trouble with it. So a defect that may seem trifling, sometimes proves serious to an injector.

COMMON DEFECTS.

As maintaining unbroken speed on the water put in motion is the first essential in keeping an injector in good working-order, any thing that has a tendency to reduce that speed will jeopardize its action. A variety of influences combine to reduce the original efficiency of an injector. Those with fixed nozzles are constructed with the orifices of a certain size, and in the proportion to each other which experiment has demonstrated to be best for feeding with the varied steam-pressures. When these orifices get worn out of the proper size, the injector will work badly; and nothing will cure it but new tubes. The tubes sometimes get loose inside the shell of the injector, and drop down out of line. The water will then strike against the side of the next tube, or on some point out of the true line, scattering it into spray, which contains no energy to force itself into the boiler. A machinist examining a defective injector, should always make sure that the tubes are not loose. Injectors that suffer from this defect will not work without a high pressure of steam. Injectors suffering from incrusted water-passages will generally work best with the steam low. Cases of the latter kind are common in calcareous districts. I have known instances where injectors got so incrusted with lime that the passages were almost closed.

Joints about injectors that are kept tight by packing must be closely watched. Many an injector that failed to work satisfactorily has been entirely cured by packing the ram-gland.

CARE OF INJECTORS IN WINTER.

During severe frosty weather, an injector can be kept in order much easier than a pump; but it needs constant watching and intelligent supervision.

To keep an injector clear of danger from frost, it should be fitted up so that all the pipes can be thoroughly drained, by frost-cocks put in for that purpose. Bends in the pipes, where water could stand, should be avoided as far as possible; and, where they can not be avoided, the lowest point should contain a frost-cock.

To run an injector successfully, thoughtful care is requisite on the part of the engineer; and, where this is given, the injector will prove itself a very economical boiler-feeder.

SELLERS INJECTOR.

When the Giffard injector was first introduced into this country, by William Sellers & Co., Philadelphia, it was a very defective boiler-feeder; but that firm effected great improvements, and led the way for making the injector the popular boiler-feeder it is to-day. They made the instrument self-adjusting, and improved its design, so that it would automatically feed, however much the pressure of the boiler varied. After numerous changes, the injector of 1876 was produced, which is shown by a sectional view in Fig.2. The Sellers injector of to-day remains substantially the same as it was when exhibited at the Centennial Exposition.

Referring to Fig.2, A is the receiving-tube, which will be closed to the admission of steam by the valve X. A hollow spindle passing through the receiving-tube into the combining-tube, is secured to the rod B; and the valve X is fitted to this spindle in such a way, that the latter can be moved a slight distance (until the stop shown in the figure engages with valve X) without raising the valve X from its seat. A second valve, W, secured to the rod B, has its seat in the upper side of the valve X, so that it can be opened (thus admitting steam to the center of the spindle) without raising the valve X from its seat, if the rod B is not drawn out any farther, after the stop on the hollow spindle comes in contact with the valve X. D is the delivery-tube, O an overflow opening into space C, K the check-valve in delivery-pipe, and P R the waste-valve. The upper end of the combining-tube has a piston N N attached to it, capable of moving freely in a cylindrical portion of the shell M M; and the lower end of the combining-tube slides in a cylindrical guide formed in the upper end of the delivery-tube.

The rod B is connected to a cross-head, which is fitted over the guide-rod J; and a lever H is secured to the cross-head. A rod L, attached to a lever on the top end of the screw waste-valve, passes through an eye that is secured to the lever H; and stops T, Q, control the motion of this rod, so that the waste-valve is closed when the lever H has its extreme outward throw, and is opened when the lever is thrown in so as to close the steam-valve X; while the lever can be moved between the positions of the stops P, Q, without affecting the waste-valve. A latch V is thrown into action with teeth cut in the upper side of the guide-rod J, when the lever H is drawn out to its full extent, and then moved back; and this click is raised out of action as soon as it has been moved in far enough to pass the last tooth on the rod J. An air-vessel is arranged in the body of the instrument, as shown in the figure, for the purpose of securing a continuous jet when the injector and its connections are exposed to shocks, especially such as occur in the use of the instrument on locomotives.

The manipulation required to start the injector is exceedingly simple,—much more so in practice, indeed, than it can be rendered in description. Moving the lever H until contact takes place between valve X and stop on hollow spindle, which can be felt by the hand upon the lever, steam is admitted to the center of the spindle, and, expanding as it passes into the delivery-tube D and waste-orifice P, lifts the water through the supply-pipe into the combining-tube around the hollow spindle, acting after the manner of an ejector or steam-siphon. As soon as solid water issues through the waste-orifice P, the handle H may be drawn out to its full extent, opening the steam-valve X, and closing the waste-valve, when the action of the injector will be continuous as long as steam and water are supplied to it.

THE NATHAN MANUFACTURING COMPANY’S MONITOR INJECTOR.

One of the most successful and enduring injectors in use is the Monitor, the distinguishing feature of which is, that the injector is constructed with fixed nozzles, that insure great durability, combined with certainty of action. The Monitor injector is shown in section in Fig.3. To start the injector, the middle cock is opened, which is the lifting-jet. When water appears at the overflow, the steam-valve is opened, and the lifting-jet closed. The work of the injector is regulated by the lazy-cock, which is the bottom handle. A movable valve, operated by an eccentric on the stem, is now employed as a lazy-cock; a common cock having been found troublesome during frosty weather. The combining-tube is attached to the line-check, and can be taken out with the check, which provides an easy means of effecting examination or repairs.

THE KORTING INJECTOR.

An examination of Fig.4 will show that this injector is a double-tube instrument; the first tube being proportioned for raising and delivering the water under pressure to the second one, which completes the operation of forcing the water into the boiler. This arrangement enables the injector to be worked through a wide range of steam-pressures without any adjustment of parts. By making the first tube proportionately small, a high power of suction is obtained, which enables the injector to feed water of such high temperature that it may be delivered into the boiler above the boiling-point. The Korting injector is operated entirely by one handle, and requires no instruction to teach its working. The feed is regulated by the patent combined regulation-valve and dirt-stop, which regulates the supply of water, and prevents the possibility of dirt reaching the injector.

THE HANCOCK INSPIRATOR.

Fig.5 gives a cross-section of the Hancock inspirator. It consists essentially of a lifting-jet and lifting-nozzle, combined with a forcing-jet and force-nozzle or injector; steam being admitted to both of these nozzles whenever the inspirator is working, to deliver the supply-water to the force-nozzle, and to force it through the nozzle into the boiler. Although both the lifting and forcing nozzles are fixed, their proportion, one to the other, is such that the inspirator requires no adjustment for changes in steam-pressure or water-supply; the waste-valve being kept closed while the instrument is in operation, except at the time of starting. The duplex nozzle arrangement of the Hancock inspirator enables that instrument to feed water of high temperature. In this respect it will act as well as the ordinary pump, besides having all the advantages of an injector. A form of inspirator is made specially for locomotive service, which is operated by a single handle.

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