Conduit systems

Explosion-proof enclosures are characterized by strong metal enclosures with special close-fitting access covers and breathers that contain an ignition to the inside of the enclosure. Field wiring in the hazardous environment is enclosed in a metal conduit of the mineral-insulated-cable type. All conduit and cable connections or cable terminations are threaded and explosion-proof. Conduit seals are put into the conduit or cable system at locations defined by the National Electric Code (Article 501) to prevent gas and vapor leakage and to prevent flames from passing from one part of the conduit system to the other. 

Having established that a finite volume of sample causes peak dispersion and that it is highly desirable to limit that dispersion to a level that does not impair the performance of the column, the maximum sample volume that can be tolerated can be evaluated by employing the principle of the summation of variances. Let a volume (Vi) be injected onto a column. This sample volume (Vi) will be dispersed on the front of the column in the form of a rectangular distribution. The eluted peak will have an overall variance that consists of that produced by the column and other parts of the mobile phase conduit system plus that due to the dispersion from the finite sample volume. For convenience, the dispersion contributed by parts of the mobile phase system, other than the column (except for that from the finite sample volume), will be considered negligible. In most well-designed chromatographic systems, this will be true, particularly for well-packed GC and LC columns. However, for open tubular columns in GC, and possibly microbore columns in LC, where peak volumes can be extremely small, this may not necessarily be true, and other extra-column dispersion sources may need to be taken into account. It is now possible to apply the principle of the summation of variances to the effect of sample volume. 

The designer must decide at inception whether to provide a cable system or a conduit system. Although both systems have specific advantages, the present trend is toward the installation of cable systems rather than conduit systems. Offshore, the vast majority of new systems are... 

Conduit systems have the advantage of offering greater mechanical protection to enclosed conductors, but they can easily lose this advantage through corrosion if not properly maintained. A conduit system which corrodes on the inside can provide false security although tlie outside appears completely sound, the system may not contain an internal explosion. Extremely rapid corrosion will occur in salt-air environments for most conduit systems of ferrous materials. In offshore environments. 

A box or fitting must be installed at each conductor sphce connection point, receptacle, switch, junction point, or pull point for the connection of conduit system. In Division 1 areas only explosion-proof boxes or fittings are allowed. General purpose gasketed cover type fittings are allowed in Division 2 areas. 

Confine internal explosions to explosion-proof enclosures and conduit systems. 

All threaded conduit referred to herein shall be threaded with an NPT standard conduit cutting die that provides -in. taper per ft. Such conduit shall be made wrench tight to (1) prevent sparking when fault current flows through the conduit system, and... 

Specifically note that Type 7 (explosion-proof) enclosures and their associated conduit systems are neither gas or liquid tight. Consequently, corrosive gases such as hydrogen sulfide and water from rain or internal condensation can accumulate with the enclosure. Premature failure of electrical devices and interconnections often results when preventive measures such as drains, air purges, and dual rated enclosures are not used to remove or exclude these corrosive elements. Type 7 enclosures are intended for indoor use. 

Figure 6.83 Low voltage energy distribution system. Flameproof enclosures are interconnected by a conduit system.

Integrity of conduit system and interface with mixed system is maintained... 

Any conduit system that has low dispersion will also provide very fast heat transfer rates. Serpentine tubing has been also used in commercial column ovens to heat the mobile phase rapidly to the column oven temperature before it enters the column. The serpentine tubing allows effective heat exchange with a minimum of heat exchanger volume to distort the concentration profile of the solvent gradient. 

The conduit system and sinuses are lined by sinus endothelial cells (SECs). SECs are flattened cells that do not form a continuous layer, especially in the wall of the medullary sinus, but contain intercellular gaps or pores. Gaps have also been demonsriated in the floor of the subcapsular sinus. FRCs and SECs might be ontogenically related and serve to filriate lymph fluid collected from all peripheral tissues, including brain interstitial tissue and cerebrospinal fluid. 

The various inputs of clastic sediment are commingled in the conduit system. Depending on the transport processes, the sediments are reorganized into distinct facies. The sedimentary facies that were devised based on transport mechanisms are ... 

Clastic sediments deposited in conduit systems can be conveniently be divided into five facies depending on the mechanism of deposition. The channel facies comprises most observed sediment piles and can be subdivided further depending on the objectives of a particular investigation. Diamicton facies and slackwater facies are deposited from suspended loads. Channel facies and thalweg facies are transported as bedload. The backswamp facies is defined to describe those residual in infiltrated clastic sediments that are deposited in place with little horizontal transport. 

Other electrical equipment is either directly buried or installed in underground conduit systems. In this type of environment, the extremes of temperature are less often experienced however localized and transient heating is experienced when power loads are high or when equipment runs near steam pipes for example. In underground installations, corrosive conditions are found based on road salts, lime extraction from concrete, and other minerals that become concentrated as water dries away. Exposure to microbes, oil run-off, decaying vegetation and other materials suggests that very stable polymers are required for this service. 

To construct the magnetic filtration set up, the magnetic filter is installed in a conduit system through which buffer is pumped by means of a peristaltic pump (Fig. 1). 

The advantages of a PVC conduit system are that it may be installed much more quickly than steel conduit and is non-corrosive, but it does not have the mechanical strength of steel conduit. Since PVC conduit is an insulator it cannot be used as the CPC and a separate earth conductor must be run to every outlet. It is not suitable for installations subjected to temperatures below 25°C or above 60°C. Where luminaires are suspended from PVC conduit boxes, precautions must be taken to ensure that the lamp does not raise the box temperature or that the mass of the luminaire supported by each box does not exceed the maximum recommended by the manufacturer (lET Regulations 522.1 and 522.2). PVC conduit also expands much more than metal conduit and so long runs require an expansion coupling to allow for conduit movement and to help prevent distortion during temperature changes. 

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