Gauges, pressure-measuring, types

Pressure reducing valves should be of steel constmction, designed for minimum and maximum operation conditions. Pressure gauges should be of ak-kon constmction. Pressure rehef valves should be of the spring-loaded type. Rupture disks may be used only as auxkiary equipment. Differential pressure measurements using mercury manometers should be avoided in ammonia service. 

Conditions of Use Bourdon tubes shoula not be exposed to temperatures over about 65°C (about 150°F) unless the tubes are specifically designed for such operation. When the pressure of a hotter fluid is to be measured, some type of hquid seal should be used to keep the hot fluid from the tube. In using either a Bourdon or a diaphragm gauge to measure gas pressure, if the gauge is below the... 

Pressure. Pressure so defined is sometimes called absolute pressure. The differential pressure is the difference between two absolute pressures. The most common types of pressure-measuring sensors are silicon pressure sensors, mechanical strain gauges, and electromechanical transducers. 

Change of pressure in a gas-phase reaction involving change of total moles of gas in a constant-volume BR (see Example 1-1) in this case, the total pressure (P) is measured and must be related to concentration of a particular species. The instrument used is a pressure gauge of some type. 

Pressure loss coefficient, 13 261 Pressure measurement, 11 783 20 644-665. See also Vacuum measurement electronic sensors, 20 651-657 mechanical gauges, 20 646-651 smart pressure transmitters, 20 663-665 terms related to, 20 644-646 Pressure measurement devices. See also Pressure meters Pressure sensors location of, 20 682 types of, 20 681-682 Pressure meters, 20 651 Pressure microfiltration/ultrafiltration,... 

Pressure is measured extensively in the chemical processing industries and a wide variety of pressure measuring methods has been developed. Some of these have already been discussed in Volume 1, Section 6.2.2, viz. the manometer (which is an example of a gravity-balance type of meter), the Bourdon gauge (an example of an elastic transducer) and mention is made of the common first element in most pressure signal transmission systems—the differential pressure (DP) cell (Volume 1, Section 6.2.3). The latter also frequently forms part of a pneumatic transmission system and further discussion of this can be found in Section 6.3.4. 

Bourdon gauges are used on gas cylinders and are also considered a type of aneroid gauge. These devices have a coiled tube (shown in Figure 3.5) and are used to measure the pressure difference between the pressure exerted by the gas in a cylinder and the atmospheric pressure. The coiled tube is mechanically coupled to a pointer (shown in red). As a gas at a pressure above atmospheric pressure enters the coiled tube, it causes it to slightly uncoil, kind of like those New Year s Eve paper noisemakers. This causes the pointer to move over a numerical scale, thereby indicating the gauge pressure in the tank. 

For our system we chose the simplest approach — a fast sample conduit with quick quench into an evacuated sample container. For temperature measurements we used a similar probe outfitted with platinum/6% rhodium-platinum/30% rhodium thermocouple. For pressure measurements the same general type probe mentioned was employed but without extracting samples. This probe had one hole opening perpendicular to the longitudinal axis of the probe such that when inserted into the reactor it could be rotated 360°. In this manner the pressures were read from a precision pressure gauge with the opening facing 0°, 90°, 180°, and 270° relative to the direction of flow in the reactor. 

The McLeod gauge will measure the pressure of dry gas to an accuracy of about 1 % and is used to calibrate other types of vacuum gauges. It is slow in operation and does not give continuous readings. It does not measure the pressure accurately if condensable vapours are present, and is limited to 10 torr if no refrigerated trap is used. 

The range of this type of vacuum gauge depends on the quality, and therefore the price, of the gauge head and associated electrical equipment. A moderately priced gauge will measure pressures within the range 10 torr to 10 toiT. The most elaborate and costly instrument is said to measure pressures as low as 10 torr. 

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