Compression manometer

Compression manometer (McLeod gauge) partial (not vapour pressures) independent (only for 760—10 permanent gases) 10 —10 ... 

U-tube manometer 80 to 1 torr compression manometer 4 to 10 torr... 

The compression manometer due to Kammerer [63] also uses only a small amount of mercury (Fig. 383). Another advantage is that the filling is greatly facilitated by a new tj pe of pumping mechanism. The instrument is supplied for the ranges of 10 to 10 torr and 1 to 10" torr and has an additional U-tube manometer for jiressures up to 80 torr. 

It should be pointed out again that all compression manometers indicate only the partial pressure of the gas component which is not condensable at the existing temperature. The presence of condensable substances is confirmed if different values of the pressure are measured in overlapping parts of two ranges [51]. 

Density Measurements. Densities were obtained using the helium displacement apparatus described by Schumb and Rittner (23) with minor modifications. Compressed nitrogen was used to raise the mercury level a steel metric scale and cathetometer were used to measure the heights of the mercury levels in the manometer and telescopes were used to observe the levels defining the constant volume. 

Two series of experiments carried out by Amagat10 confirmed Regnault s results for hydrogen, and proved methane to resemble nitrogen in being more compressible than theory demands. In one set of observations he employed pressures up to 400 atmospheres, measured directly by means of a manometer in the other the gas was submitted to pressures up to 3000 atmospheres. Amagat s work was confirmed by the researches of Wroblewsky.11... 

Because gases are compressible, they exert pressure on their surroundings. Pressure is the force that is exerted over a unit area. For example, the atmosphere exerts a pressure known as atmospheric pressure. The Earth s atmosphere is a function of the location and the weather conditions, and it decreases with a higher altitude. The unit of pressure commonly used in chemistry is the atmosphere (atm). The standard atmosphere is 1 atm or a measurement of 760 millimeters of mercury (mm Hg or torr) on a manometer. 

HF is supplied in steel compressed-gas cylinders. Because the boiling point of HF is 19 °C, most of the HF in the cylinder is liquid, and the pressure is low (about SOOTorr). When HF cylinders are stored for a long time, pressure in the cylinders can build up due to reaction of HF with iron to form hydrogen. Newly purchased cylinders have been received with high pressure open such cylinders very cautiously the first time. If there is high pressure in the cylinder, mercury in the vacuum-line manometer can be blown out of the top and scattered about the hood. ... 

FIG. A. 10. An improved perfusion unit, Tliis unit FIG. A. 13. An improved constant volume manometer. Tire inclusion of a operates with compressed air. Tire components are Kel-F tyPe greaseless tap Permits tire measurement of grease sensitive easily assembled and are interchangeable with tliose gases. Tire Rotaflow tap between tire U-tube and tire reservoir prevents of similar units. contamination of the Hg. 

Its principle of operation is based on Boyle s Law, in that a fixed large volume of the gas at the unknown pressure is compressed to a fixed small volume. The pressure of the gas following compression is measured by a mercury manometer, and the initial pressure is calculated from this pressure and the volume ratio. Pressures as low as 10-6 mm. Hg can be accurately measured by this gage. A major cause for error is the presence of condensable vapors in the gas being measured. Under such conditions the pressure obtained with this gage is closer to the partial pressure of noncondensables than the total pressure. It is not exactly equal to the partial pressure of noncondensables, however, because the condensable vapors may exert a significant vapor pressure after condensation. 

Conversion factors for mercury manometer pressure units are calculated using die standard value for the acceleration of gravity and die density of mercury at die stated temperature. Additional digits are not justified because the definitions of the units do not take into account die compressibility of mercury or the change in density caused by the revised practical temperature scale, ITS-90. Similar comments also apply to water manometer pressure units. Conversion factors for conventional mercury and water manometer pressure units are based on ISO 31-3. 

Fig. 1.5 A schematic layout of an intensifier system (B) to experimental cell, (C) low-pressure compressor (700 MPa), (I) intensifier cylinder, (M) resistance manometer, (P) main oil ram and press, (S) separator cylinder, (U) compression cylinder, and (V) valves. Here, R is the multiplication ratio of the cylinders.

Fig. 1.6 A cross section of a 1.6 GPa cylinder (B) to experimental cell, (C) compression chamber (diameter, 16 mm), (H) piston head, (1) inner cylinder under radial compression, (M) to resistance manometer, (P) high-pressure outlet plug with electrical leads, (U) unsupported-area, Bridgman-type, sliding-piston arrangement. The force applied to the piston by the oil ram for a pressure of 1.6 GPa is F= 350 kN.

There are no special requirements for fhe insfrumenfa-tion used to measure the temperature and pressure of the compressed air. Orifice gauges and hof wire anemometers measure flow rate in a relatively precise manner. As regards to steam, the instrumentation needs to resist not only pressures but also high temperature. In the case of manometers and pressure sensors it is advisable to use cooling separators filled wifh silicon oil. It is appropriate to use orifice gauges to measure flow rate because high temperature does not affect them. 

The system shown in Fig. 2.38 is used to measure the density of a fluid in a tank. Compressed air or nitrogen bubbles at a very low rate through two dip tubes, whose ends are vertically 1.00 m apart. The difference in pressure between the two dip tubes is measured by a water manometer, which reads 1.5 m of water. The gas flow rate is so slow that the gas in the dip tubes may be considered a static fluid. The density of the gas is 1.21 kg/m. What is the density of the fluid in the tank ... 

Compression manom ers of the McLeod type can also be employed in the 760— 1 min range. Since, however, their main field of application lies in the range of 10 to 10 mm pres.sure, they will be discussed under the latter heading. For the range of 0 to 60 mm water column electronic contact manometers are now-in use [36a]. 

The principle of this manometer, which gives a reliable reading only for permanent gases, is the compression of a certain volume of the gas, measured at the pressure to be determined, to a small volume in a capillary tube. The gas sample is in this way brought to a higher pressure that can readily be measured. The pressure p of the original gas can then be calculated with sufficient accuracy by means of the formula... 

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