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The Giffard injector
52
Meehanles, _Physics, and Chemistry.
be exemplified by observing the marks left on a polished glass-surface from tile light blows of a steel centre punch. The point of the punch drives in an atom of tile glass, and the fracture extends some distance into tim interior, expanding downwards in the ferm of a truncated cone. The polariseope shows that the conical centre is in a state of eompres~ sion, and that the surrounding exterior portion of the glass is also under strain. The smooth, round edge of a glazier's diamond, when drag'n over a polished glass surface, burnishes down and compresses the glass beneath the cut, and in the case of thin sheets the wedgelike force of the compressed line splits the glass nearly through, but 'when the glass is thick and rigid, as plate glass, unless the sheet is bent back and broken through immediately after the cut, greater difficulty will be experienced if allowed to remain for a time, for the compressed line of glass will speedily tear up the portion on both sides, leaving a wide ragged grove in place of the original clean and scarcely visible line.
For the Journal of the Franklin Institute.
:By CHARLES E. EMERY,Asst. Eng. U.S.N. The writer, by permission, recently tried some brief experiment s ~vlth a view of ascertaining the cost of forcing water with a Giffard injector, an account of which may not be uninteresting, inasmuch as there is a wide difference of opinion in regard to the economy of using this device for feeding boilers. The injector employed was one of moderate size attached to the auxiliary boiler of the U. S. Steam Expansion E~periments. Tile water was supplied from a tank, with a head of from three to four feet, and was delivered by the injector into a pipe with two branches, one connected to the boiler, and the other to a water chamber, having attached to it a steam gauge and safety ~'alve. Each branch of the pipe was provided with a stop valve, so that the water could at pleasure be forced into the boiler or out of the safety valve on the water chamber at the desired pressure shown by the gauge. :Before starting an experiment, the boiler was supplied v.'ith sufficient water to last an hour without feeding, the boiler and ~vater chamber gauges being compared by opening valves on both branches of lower pipe when the injector was in operation. The water connexion with boiler was then carefully closed. During the experiments the water was measured before being supplied to the injector; the safety valve on the w~ter chamber was loaded to the desired pressure, and the injected water passed through it, and was again carefully measured, the increase in quantity showing the amount of steam drawn from the boiler. The "overflow " water was collected in a separate vessel and returned to the first tank. The following table shows the b e s t results of the experiments under the conditions expressed. The pressures and temperatures are the means of records taken every fifteen " minutes,
The Giffard Injector.
Tl~e ~,;ffard Injector.
~
Durationof Experiment.
o
~
~
.~
~
53
o
~
•
t ¢'1
T .~
~
o
~ o
5~
54
Mechanics, Physics, and Cl~emistry.
In three of the above experiments the average pressure of steam exceeded that of the water. In No. 3 the water pressure was in excess, and it was found that it could be carried much higher without stopping the operation of the injector. In one instance, with seventy pounds of steam, by weighting the safety valve on water chamber, the water pressure was increased to one hundred and ten pounds, which caused a larger " overflow," and less water was delivered under pressure. The above would seem to indicate that the injector forces, against pressure, sufficient water to condense the steam used. Two of the experiments fall short of this by calculation, due probably to the h.eating of the small quantity of " overflow " water. The better result of No. 2 over No. 1 was doubtless occasioned by the adjustment of the valves, a smaller quantity of water being delivered, but at a less comparative cost. ~qos. 3 and 4 indicate that small changes in the relative pressures of" steam and water have some little influence on the ratio. Assuming as the best result that one pound of steam will force sixteen pounds of water against a pressure of sixty pounds, or one hundred and thirty-eight feet high, thus performing 2208 foot-pounds of work, and, bearing in mind that few steam engines use more than one pound of steam per horse power per minute, we find that the injector requires nearly fifteen times the quantity of steam used by a steam engine to do the same work, or a steam pump should force nearly fifteen times as much water as an injector, when using the same quantity of steam. For feeding cold water to a boiler the injector is more economical, as it returns through the feed water all the heat it takes out in the steam, and the pump, though it requires less steam, wastes all the heat of what it does receive. When, however, the pump is used in connexion with a condensing engine or heater, so that the temperature of the feed water is raised to upwards of one hundred degrees, there can be no question of its superior economy, as it will convey to the boiler, by means of the feed water, a greater number of units of heat from the exhaust steam of the main engine than will be required for tile steam to drive the pump itself. T h e value of an injector, as simply an auxiliary feed to a steam boiler when the engines are stopped, cannot be doubted, but for constant use as a boiler feed, under ordinary circumstances, the force pump would seem to be preferable, and that can be most economically ope. rated by the main engine, for the cost of the power in a small engine is proportionately much greater than in a large o n e - - a point apparently ignored in these days of independent feed, air, and circulating pumps.
Alloying of Iron and Steel with Tungsten. From the London Mechanics' Magazine, September, 1865.
There has been considerable controversy from time to time as to the effect which is produced upon iron and steel by alloying them with
Meehanles, _Physics, and Chemistry.
be exemplified by observing the marks left on a polished glass-surface from tile light blows of a steel centre punch. The point of the punch drives in an atom of tile glass, and the fracture extends some distance into tim interior, expanding downwards in the ferm of a truncated cone. The polariseope shows that the conical centre is in a state of eompres~ sion, and that the surrounding exterior portion of the glass is also under strain. The smooth, round edge of a glazier's diamond, when drag'n over a polished glass surface, burnishes down and compresses the glass beneath the cut, and in the case of thin sheets the wedgelike force of the compressed line splits the glass nearly through, but 'when the glass is thick and rigid, as plate glass, unless the sheet is bent back and broken through immediately after the cut, greater difficulty will be experienced if allowed to remain for a time, for the compressed line of glass will speedily tear up the portion on both sides, leaving a wide ragged grove in place of the original clean and scarcely visible line.
For the Journal of the Franklin Institute.
:By CHARLES E. EMERY,Asst. Eng. U.S.N. The writer, by permission, recently tried some brief experiment s ~vlth a view of ascertaining the cost of forcing water with a Giffard injector, an account of which may not be uninteresting, inasmuch as there is a wide difference of opinion in regard to the economy of using this device for feeding boilers. The injector employed was one of moderate size attached to the auxiliary boiler of the U. S. Steam Expansion E~periments. Tile water was supplied from a tank, with a head of from three to four feet, and was delivered by the injector into a pipe with two branches, one connected to the boiler, and the other to a water chamber, having attached to it a steam gauge and safety ~'alve. Each branch of the pipe was provided with a stop valve, so that the water could at pleasure be forced into the boiler or out of the safety valve on the water chamber at the desired pressure shown by the gauge. :Before starting an experiment, the boiler was supplied v.'ith sufficient water to last an hour without feeding, the boiler and ~vater chamber gauges being compared by opening valves on both branches of lower pipe when the injector was in operation. The water connexion with boiler was then carefully closed. During the experiments the water was measured before being supplied to the injector; the safety valve on the w~ter chamber was loaded to the desired pressure, and the injected water passed through it, and was again carefully measured, the increase in quantity showing the amount of steam drawn from the boiler. The "overflow " water was collected in a separate vessel and returned to the first tank. The following table shows the b e s t results of the experiments under the conditions expressed. The pressures and temperatures are the means of records taken every fifteen " minutes,
The Giffard Injector.
Tl~e ~,;ffard Injector.
~
Durationof Experiment.
o
~
~
.~
~
53
o
~
•
t ¢'1
T .~
~
o
~ o
5~
54
Mechanics, Physics, and Cl~emistry.
In three of the above experiments the average pressure of steam exceeded that of the water. In No. 3 the water pressure was in excess, and it was found that it could be carried much higher without stopping the operation of the injector. In one instance, with seventy pounds of steam, by weighting the safety valve on water chamber, the water pressure was increased to one hundred and ten pounds, which caused a larger " overflow," and less water was delivered under pressure. The above would seem to indicate that the injector forces, against pressure, sufficient water to condense the steam used. Two of the experiments fall short of this by calculation, due probably to the h.eating of the small quantity of " overflow " water. The better result of No. 2 over No. 1 was doubtless occasioned by the adjustment of the valves, a smaller quantity of water being delivered, but at a less comparative cost. ~qos. 3 and 4 indicate that small changes in the relative pressures of" steam and water have some little influence on the ratio. Assuming as the best result that one pound of steam will force sixteen pounds of water against a pressure of sixty pounds, or one hundred and thirty-eight feet high, thus performing 2208 foot-pounds of work, and, bearing in mind that few steam engines use more than one pound of steam per horse power per minute, we find that the injector requires nearly fifteen times the quantity of steam used by a steam engine to do the same work, or a steam pump should force nearly fifteen times as much water as an injector, when using the same quantity of steam. For feeding cold water to a boiler the injector is more economical, as it returns through the feed water all the heat it takes out in the steam, and the pump, though it requires less steam, wastes all the heat of what it does receive. When, however, the pump is used in connexion with a condensing engine or heater, so that the temperature of the feed water is raised to upwards of one hundred degrees, there can be no question of its superior economy, as it will convey to the boiler, by means of the feed water, a greater number of units of heat from the exhaust steam of the main engine than will be required for tile steam to drive the pump itself. T h e value of an injector, as simply an auxiliary feed to a steam boiler when the engines are stopped, cannot be doubted, but for constant use as a boiler feed, under ordinary circumstances, the force pump would seem to be preferable, and that can be most economically ope. rated by the main engine, for the cost of the power in a small engine is proportionately much greater than in a large o n e - - a point apparently ignored in these days of independent feed, air, and circulating pumps.
Alloying of Iron and Steel with Tungsten. From the London Mechanics' Magazine, September, 1865.
There has been considerable controversy from time to time as to the effect which is produced upon iron and steel by alloying them with