Pneumatic gauge

In 1952-1959 all pneumatic gauges were worn-out and replaced with a float in a stilling well. 

Hornbcek Pneumatic gauge from 1890. Float in stilling well from app. 1959. Differential pressure transducer — CTD (Conductivity, Temperature, Depth) — from June 2000. 

Another more or less contacting thickness measurement technique is pneumatic gauging. The device consists of a nozzle fixed in position relative to a stop. Air at a constant supply pressure passes through a restriction and discharges through the nozzle see Fig. 4.21. 

The receiving gauge in the control room works on the transmitted pneumatic pressure, 15 psi giving full scale, but has its dial calibrated in terms of the plant pressure that it is indicating. The Bourdon tube of such a gauge is capable of withstanding only a limited amount of overpressure above 15 psi before it will burst. Furthermore, the material of the Bourdon tube is chosen for air and may be unsuitable for direct measurement of the process fluid pressure. 

Pneumatic controllers, which may include part of the sensing instrument, are supplied with compressed air at 1 bar gauge which is allowed to escape from an orifice controlled by a detector. The resulting pressure modulates about 0.4 bar and is used in a servo... 

In front of the building a timber floor protected by a eave should be laid. Trucks coming and going with materials should be moved by hand. Trucks with pneumatic-tyred wheels or barrows with bronze wheels are best for this purpose. If a narrow-gauged track is to be used, in the vicinity of buildings holding blackpowder, the rails should be of wood and the trucks should be fitted with bronze wheels. 

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. 

The pressure control system is directly connected to the gas refill system. Pressure is measured by pressure gauges at the top of each column. It is kept constant by the subsequently installed pneumatic regulated expansion valves. If the pressure of the second regeneration column becomes too low the gas refill system is activated (see chapter 2.1.4). 

Figure 5.2.1. Simplified diagram of a Py-GC system (not to scale). The pyrolyser is schematized as a heated filament type. A piece of a deactivated fused silica line is passed through the injection port of the GC and goes directly into the pyrolyser. This piece of fused silica is connected to the column, which is put in the GC oven. The pneumatic system consists of (1) a mass flow controller, (2) an electronic flow sensor, (3) a solenoid valve, (4) a backpressure regulator, (5) a pressure gauge, and (6) septum purge controller. The connection (7) is closed when working in Py-GC mode, and connection (8) is open. (Connection (7) is open when the system works as a GC only.) Connection (9) is closed and connection (10) is open when the GC works in splitless mode (purge off). Connection (10) is closed and connection (9) is open when the GC works in split mode (purge on). No details on the GC oven or on the detector are given.

Most pneumatic conveyors operate under positive pressure, with a blower or compressor feeding air (or occasionally nitrogen) at 1 to 5 atm gauge pressure into the system. The ratio of solids to gas is usually higher than in vacuum systems. Sometimes the gas is recycled to the blower or compressor inlet in a closed system to save a valuable gas or prevent loss of dust to the atmosphere. 

Transducers Many measurements cannot be used for control until they are converted to physical quantities (such as electric voltage or current, or a pneumatic signal, i.e., compressed air or liquid) which can be transmitted easily. Transducers are used for that purpose. For example, strain gauges are metallic conductors whose electric resistance changes when they are subjected to mechanical strain. Thus they can be used to convert a pressure signal to an electric one. 

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