The Bourdon Gauge

It may be noted that the pressure measuring devices (a) to (e) all measure a pressure difference AP(— Pj — P ). In the case of the Bourdon gauge (0, the pressure indicated is the difference between that communicated by the system to the tube and the external (ambient) pressure, and this is usually referred to as the gauge pressure. It is then necessary to add on the ambient pressure in order to obtain the (absolute) pressure. Even the mercury barometer measures, not atmospheric pressure, but the difference between atmospheric pressure and the vapour pressure of mercury which, of course, is negligible. Gauge pressures are not. however, used in the SI System of units. 

All over the world instruments of the "Bourdon gauge type" are used, and many manufacturers make such devices. Some of the best instruments of the Bourdon-type are from [53] with standard ranges up to approx. 7000 bar with a tolerance of only 0.01 % of span, provided with up to 16 inch diameter dials. 

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. 

Suppose you have a cylinder of oxygen gas, and the Bourdon gauge indicates a pressure of 0 psi. If the atmospheric pressure is 14 psi, what is the pressure... 

The high-pressure inlet is attached to a f in. cross to provide ports for gas introduction, pressure measurement, and thermocouple placement just in front of the frit. The Bourdon gauge (0-10 bar) should be connected via a tee to a purge valve to facilitate gas changes. Before use the assembly should be tested at 10 bar for leaks. Thermal insulation such as glass wool should be wrapped around the frit assembly to keep the expansion as adiabatic as possible. 

A 20-fC gas cylinder in your laboratory can hold pressures up to 400 atm. The Bourdon gauge on the cylinder reads 380 atm one morning when the temperature is 55°F. How high can the temperature go before it becomes advisable to move to a different laboratory ... 

Provided that there is a change in the number of moles upon reaction and the stoichiometry of the process is known, pressure measurements may be used to determine the order of the reaction according to equation (A). Thus Letort found that the order for the decomposition of AcH was with respect to initial concentration and 2 with respect to time (see p. 2). Such direct conclusions cannot usually be drawn from pressure measurements with oxidation reactions. However, direct information may be obtained from a very neat differential system devised by Du-gleux and Frehling (Fig. 9). Vj and V2 are two RV s, of different size connected to the inside and outside of the Bourdon gauge J. Rj allows simultaneous introduction of mixtures into Vj and V2 Any fluctuation in temperature of the furnace is thus compensated for. Rapid reactions and the direct effect of promoters and inhibitors on an oxidation may be studied. This apparatus may well be useful with other systems. 

The Bourdon gauge consists of a flattened, thin-walled metal tube bent into the form of an arc or C shape as illustrated in Figures 4.7 and 4.8 [3]. One end of the tube is fixed and securely sealed and bonded to a threaded connection called a socket. The other end is tightly sealed and free to move. At atmospheric pressure (zero gauge pressure) the tube is undeflected and for this condition the gauge pointer is calibrated to read zero pressure [4]. However, when pressure is applied into the fixed end of the tube, the effect of the forces tends... 

The precision can be greater than the resolution, as illustrated in Figure 2.5. The Bourdon gauge reads pressure from 0 bar to 6 bar and has ticks at 1 bar intervals. The tip of the needle is very narrow and it is reasonable to estimate the needle position to a precision of at least 0.2 bar, if not 0.1 bar. 

The Bourdon gauge was developed in 1849 by the French engineer Eugene Bourdon. The gauge is based on the principle that a tube will expand when a pressure is applied to it. The tube is closed at one end and open to the process fluid at the other end. The tube is in the shape of an arc and the curvature of the arc increases when pressure is applied to it and it decreases when the pressure drops. The closed end of the tube is connected to a pivot and a spring that translates the movement of the arc into a rotation of a needle. The tube can be made of many different metals— bronze, steel, brass, etc.—depending on the application. 

Solution 5.1a. The Bourdon gauge should be placed as close to the cylindrical body to minimize the total volume of gas that remains unheated. Assuming that this dead volume is negligible, Amontons Law of Pressure-Temperature applies ... 

The temperature of water in a beaker on a hot plate is measured by a constant-volume thermometer. The cylindrical body of the thermometer is 250 ml. It is connected directly to a Bourdon gauge and the barometric pressure is 1.0 bar. One hundred grams of isopropanol is placed in the body of the thermometer. What is the temperature of the water if the pressure recorded on the Bourdon gauge is 10 kPa ... 

The pressure is held constant by the controller G and is measured by the Bourdon gauge, H. Flow rates are determined at atmospheric pressure by a gasometer I and the mixture is analysed by a gas chromatograph J. The calorimeter must be carefully designed to ensure complete mixing without producing a significant pressure drop. Trial measurements in which the same substance is used in both... 

The most widely used pressure instrument in the chemical industry is the Bourdon gauge, which may be used for higher pressures (Fig. 5.2). A common type consists of a metal tube, closed at one end, and bent in the arc of a circle, which tends to increase its radius (straighten out) on the application of pressure within the tube. A connecting link from the free end of the tube is joined to a pivoted indicating pointer placed in the centre of a dial. 

The Bourdon gauge may be modified to measure the pressure of corrosive liquids or gases, which would corrode the metal tube, by sealing it oif with a flexible diaphragm. 

Eugene Bourdon was a watchmaker and engineer who in 1849 invented the Bourdon gauge, apressure measuring instrument still in use today. It could measure pressures up to 100,000 psi - quoted from Wikipedia.com. 

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