Pressure gauge

“ As soon as 95 water gas gauge pressure has entered this box, the diaphragm rises and closes the valve, which does not re-open until the lights are turned on, when it admits gas at the same rate at which it is consumed at the burners. Each jet can be regulated to a given size, so that it cannot blaze and cause waste, and all the lights in a carriage can be turned off or half-off, by a key at the end of the carriage. Finally, each carriage has a pressure gauge to indicate the pressure of gas in the cylinders, and to shew when the supply is exhausted. ”

“ Bourdon tube pressure indicator. The tube is of flat section, and its curved portion expands with the pressure, operating a finger on the dial by rackwork.
791. Worm gear and dial to register the number of revolutions. See No. 1559.
Other forms of pressure gauges are—1st. The mercurial gauge, in which the pressure is indicated by the height of a column of mercury in a glass tube. 2nd. The water gauge, in which a column of water replaces the mercury. 3rd. The spring balance (see No. 1729) . See also Nos. ”

“ We vaporize at 20° a certain quantity of the liquid, and the vapors fill the known capacity of the pump. The pressure of the gases in the interior is ascertained by a pressure gauge, and this pressure should be constant if care is taken to act upon a sufficient mass of liquid and with moderate speed. When the receiver of the air-pump is full of vapors, communication between it and the test-tube is shut off, and communication is effected with a second test-tube, like the first, plunged into the same water at 20°. Care must be taken beforehand to create a perfect vacuum in this test-tube. ”

“ By raising or lowering the pressure the temperature can be made to rise or fall. A steam vulcanizer is a tightly sealed vessel which contains water and which is provided with a thermometer or a pressure gauge as well as a safety-valve, safety disc or safety plug. By keeping the gauge at constant pressure or by keeping the thermometer constant the temperature can be limited and kept steady. The following table gives some pressure in pounds per square inch with temperatures corresponding to steam of such pressures ”

“ If the engine is to stop for any length of time, shut off the impermeator and the injection supply.
A vacuum gauge is an instrument for measuring the total or absolute pressure, or pressure above a perfect vacuum, and it is used to indicate the degree of vacuum that exists in the condenser, which, when the various joints about the cylinder and condenser are tight, averages about 27 inches of mercury when the temperature in the hot well is about 100° Fahrenheit. ”

“ In small machines, and also in some large ones, the stress is applied by screw gearing instead of by hydraulic pressure. Springs are sometimes used instead of weights to measure the stress, and another plan is to make one end of the specimen act on a diaphragm forming part of a hydrostatic pressure gauge. ”

“ Connected with the cushion is a pressure gauge, and a tube with a cock, for charging the cushion with air from the lungs. Experience shows what pressure is necessary with any given paper, and the gauge enables one to know that the pressure is neither deficient nor in excess of that which is safe for the glass. ”

“ The 'manometer' is generally known as a pressure gauge.—TRANS.
[2] Ruhmkorff's apparatus consists of a Bunsen pile worked with bichromate of potash, which makes no smell; an induction coil carries the electricity generated by the pile into communication with a lantern of peculiar construction; in this lantern there is a spiral glass tube from which the air has been excluded, and in which remains only a residuum of carbonic acid gas or of nitrogen. When the apparatus is put in action this gas becomes luminous, producing a white steady light. ”

“ The principle of construction of the dial steam gauge is, that the pressure may be indicated by means of a pointer in a divided dial similar to a clock face, but marked in division, indicating pounds pressure per square inch instead of hours and minutes. ”

“ In selecting a new gauge you will be better satisfied with a gauge having a double spring or tube, as they are less liable to freeze or become strained from a high pressure, and the double spring will not allow the needle or pointer to vibrate when subject to a shock or sudden increase of pressure, as with the single spring. A careful engineer will have nothing to do with a defective steam gauge or an unreliable safety valve. ”

“ The pressure in the thermometric bulb T is adjusted to equality with the standard by means of a delicate oil-gauge G of small bore, in which the difference of pressure is observed by means of a cathetometer microscope. This kind of gauge permits the rapid observation of small changes of pressure, and is far more accurate and delicate than the mercury manometer. The fundamental measurement of the volume of the overflow in terms of the weight of mercury displaced at 0°C. involves a single weighing made at leisure, and requires no temperature correction. ”

“ The gauge used to estimate the degree of pressure to which the gas within the condensing tube was subjected was of the same kind as those formerly described, [5] being a small tube of glass closed at one end with a cylinder of mercury moving in it. So the expression of ten or twenty atmospheres, means a force which is able to compress a given portion of air into 110th or 120th of its bulk at the pressure of one atmosphere of thirty inches of mercury. ”

“ Suppose a fan run at constant speed with different resistances and the compression pressure, discharge and brake horse-power measured. The results plot in such a diagram as is shown in fig. 213. The less the resistance to discharge, that is the larger the opening in the air trunk, the greater the quantity of air discharged at the given speed of the fan. On the other hand the compression pressure diminishes. The curve marked total gauge is the compression pressure + the velocity head in the discharge pipe, both in inches of water. ”

“ But air is a poor conductor; it acquires heat faster than it can give it off to the water surrounding the cylinders. In compound air compressors the air compressed in one cylinder is cooled before being passed on to the next cylinder, where it is further compressed. The heat loss in compressing air in a single stage up to 100 pounds gauge pressure is about 30 per cent. Air that enters a compressor at the normal pressure of the atmosphere and with an initial temperature of 60 degrees F., if not cooled will become heated to 415 pounds gauge pressure. ”

“ The force-pump is then connected with a gauge, and is worked until a high pressure has been registered upon it, in order that should the pipes have any latent weaknesses, the pressure exerted will develop and discover them. ”

“ The large gauge became unsafe in 1896 and was removed, but the observations for the previous ten years entirely confirm this result, the importance of which is obvious. The same result may be deduced from the Tower Bridge observations. Power is required to raise the great bascules and the power needed depends on the direction of the wind. From observations on the power some estimate of the average wind pressure on the surface may be obtained, and this is found to be less than the pressure registered by the small wind gauges. ”

“ Fixed pressure gauges, however, connected with every item of a plant are extremely useful, and should be employed in all large installations, as they afford great aid in observing and controlling the working, and in locating the exact position of any block. ”

“ A check valve is almost indispensable in using a hydraulic gauge, as the pressure is often suddenly removed and the momentum of the hand will throw the pinion out of gear with the toothed arc, and is liable to break the hair-spring. ”

“ The two-stage or multi-stage system of air compression is used generally for high pressure work. The system is most usefully employed between 40 and 120 pounds gauge pressure. For the moderate working pressure of 90 to 100 lbs., the two-stage compression has demonstrated its efficiency chiefly for the reason, that the heat generated in the last half of the stroke75 of a single compressor is by the two-stage process greatly reduced. ”

“ The fact that the heating effect of compressing air from an initial pressure of 10 pounds absolute to 90 pounds gauge pressure is theoretically equivalent to that of compression to 132 pounds at sea level, makes a two-stage arrangement more imperative in high level work than under ordinary conditions. ”

“ These have been found to answer well and enable the experimenter to graduate with a nicety the pressure to which the gas is exposed during measurement. By employing a cylinder filled with mercury instead of the usual caoutchouc tubing small bubbles of air are prevented from entering the gauge along with the mercury. An adjustable brace or support is used which prevents accident to the cylinder when the pump is inclined for the purpose of pumping out the vacuum-bulb. ”

“ The subsidence of pressure resulting from explosives being about as sudden as the creation of pressure, causes the pointer to move too rapidly for correct ocular observation, on which account a static electric current is employed, causing a stream of electric sparks to shoot off from the end of the pointer, B, to the brass outer ring, M. The gauge is insulated for that purpose by glass plate, S, which is secured concentrically to the gauge proper and the ring, M. Binding posts for the electric wires are provided at O and P, which wires are shown in Fig. ”

“ At each stroke of the piston which expands the air under the pneumatic receiver when a vacuum is to be created, a lowering of pressure is produced, and undoubtedly a change of temperature. It can be determined approximately, at least, by observing the position of the manometer at the instant after the dilatation has taken place, and again after a time long enough for the temperature to have returned to its original point, that of the surrounding bodies. ”

“ Now, if the piston should be loaded with a weight, the pressure on the outside would be that due to the atmosphere, plus the weight, while the pressure from the inside is simply equal to atmospheric pressure; thus the piston is forced to descend, but as the air inside of the cylinder has no means of escape, the volume it fills being diminished, its pressure rises until the pressure under the piston balances that above it. ”

“ It happens that we are living in an atmosphere of about fifteen pounds pressure per square inch, and it is very convenient oftentimes in our computations to take the pressure of the atmosphere as our zero, and reckon all other pressures above and below this. If all our pressure scales read from absolute zero, the pressure of a perfect vacuum, then all this confusion would be avoided. We have not used the absolute zero in our diagram, because all our gauges are graduated with their zero at atmospheric pressure, and it is customary to speak of pressures above and below the atmospheric. ”

“ The pressures rise in an even, gradual line from the end of the compression curve, and instead of having a sharp peak at the end of the combustion, as in a gas engine, the top of the curve is broad and greatly resembles the indicator diagram of a steam engine. The compression curve constitutes a greater proportion of the pressure line than that of a steam engine, the rise of pressure due to the ignition being very slight in comparison to the height of the compression curve. ”

“ Thus, when by increase of pressure the vacuum box is compressed, the mechanism transfers the movement to the index, and it moves to the right; when the vacuum box bulges out under diminished pressure, the mechanical motion is reversed, and the index moves to the left. As the index traverses the dial, it shows upon the scale the pressure corresponding with that which a good mercurial barometer would at the same time and place indicate ”

“ Plainly, the engineer should begin by sending into his compressor air as cool as possible, and during compression he should keep the temperature of the air as low as he can. Moderate pressures, to fifty pounds per square inch or so, may well be effected at a single stroke, the air as it issues from the compressing cylinder passing through pipes immersed in cold water, a similar chilling stream being sent around the cylinder walls themselves. This air at fifty pounds, duly cooled, may now, if we wish, be brought to say 100 pounds pressure in a second cylinder ”

“ The unit of measurement of gas pressure is that pressure which will cause a difference of water level of one tenth of an inch in the two legs of a V-shaped tube when one end is connected with the gas main and the other end is left open to the outer air. Ten tenths, or one inch, is the standard, or normal pressure.
Any appliance—even a gas-burner—operates to best advantage ”

“ The divisions running horizontally represent centimeters of water or of mercury, according to the strength of the spring, M, which should be so constructed as to be in relation with the pressure. The operation of the apparatus may be readily understood.
GAS INDICATOR OF MANOMETER.
When the gas reaches the pressure chamber, the spring, M, contracts, and consequently the counterpoise descends, and causes the cord, O, which carries the slide and writing style, to wind around the pulley. When the pressure diminishes, the movement takes place in an opposite direction. ”