Air leaks

Place 45 g. of benzamide (Section IV, 188) and 80 g. of phosphorus pentoxide in a 250 ml. Claisen flask (for exact experimeutal details on the handling and weighing out of phosphoric oxide, see under Acetamide, Section 111,111). Mix well. Arrange for distillation (Fig.//, 29, 1 or Fig. II, 20, 1) under reduced pressure use a water pump with an air leak in the system so that a pressure of about 100 mm. is attained. Heat the flask with a free flame until no more liquid distils the nitrile will pass over at 126-130°/100 mm. Wash the distillate with a little sodium carbonate solution, then with water, and dry over anhydrous calcium chloride or magnesium sulphate. Distil under normal pressure (Fig. II, 13, 2 or II, 13, 6) from a 50 ml. flask the benzonitrile passes over as a colourless liquid at 188-189° (compare Section IV,66). The yield is 28 g. 

This pressure is readily attained by placing an air leak between the water pump and the apparatus or, better, with the aid of a manostat. Figs. II, 23, 4-7. 

Air leaks into the system if the pump suction is below atmospheric pressure. 

Air is usually the basic load component to an ejector, and the quantities of water vapor and/or condensable vapor are usually directly proportional to the air load. Unfortunately, no reliable method exists for determining precisely the optimum basic air capacity of ejectors. It is desirable to select a capacity which minimizes the total costs of removing the noncondensable gases which accumulate in a process vacuum system. An oversized ejector costs more and uses unnecessarily large quantities of steam and cooling water. If an ejector is undersized, constant monitoring of air leaks is required to avoid costly upsets. 

To determine the amount of air leak in an existing system, estimate the total volume of the system. Operate the ejector to secure a pressure somewhat less than 15 inches Hgabs. Then isolate the ejector from the system. Measure the time required for a rise in pressure in the vessel (say 2 inch Hg). It is essential that the absolute pressure does not rise above 15 inches Hg abs during this time. The following formula will then give the leakage ... 

First, the test described above must be run. Then a known air leak must be introduced to the system. This can be done by means of a calibrated air orifice. A second test is made, obtaining a new pressure rise and time. The unknown leak is then given by... 

Pressure Zero shift, air leaks in signal lines. Variable energy consumption under temperature control. Unpredictable transmitter output. Permanent zero shift. Excessive vibration from positive displacement equipment. Change in atmospheric pressure. Wet instrument air. Overpressure. Use independent transmitter mtg., flexible process connection lines. Use liquid filled gauge. Use absolute pressure transmitter. Mount local dryer. Use regulator with sump, slope air line away from transmitter. Install pressure snubber for spikes. 

Macchiarini, R, Wain, J., Almy, S. and Dartevell, R, Experimental and clinical evaluation of a new synthetic, absorbable sealant to reduce air leaks in thoracic operations. J. Thorac. Cardiovasc. Surg., 117, 751-758 (1999). 

Bee.iusa the nitrogen pressure was unreliable, it was difficult to maintain a pressure of 0.5 inch water gauge in the metal cabinet. Workers complained that the safety switch kept isolating the electricity supply, so an electrician reduced the setpoint first to 0.25-inch and then to zero, thus effeciocly bypassing the switch. The setpoint could not be seen unless the cover of the switch was removed and the electrician told no one what he had done. The workers though I lie wa,s a good electrician who had prevented spurious trips. Solvent and air leaked into the cabinet, as ilready described, and the next time the electricity supply was switched there was an explosion. 

Moisture from Air Leaks through Cracks and Apertures... 

To prevent leaks of carbon monoxide and hydrogen from the glands of a number of compressors getting into the atmosphere of the compressor house, they were sucked away by a fan and discharged through a small vent stack. Air leaked into the duct because there was a poor seal between the duct and the compressor. The mixture of air and gas was ignited by lightning. 

To provide a constant, controlled supply of fresh air to maintain proper indoor air quality and prevent moisture damage, there are three basic ventilation strategies constant supply, constant exhaust, and balanced systems. Constant supply systems provide a continuous flow of fresh air to living areas and force stale air out through air leaks and kitchen and bathroom Ian vents. Constant exhaust systems continuously remove stale air while allowing fresh air to... 

Air in leakage, depending on the quantity, can create an explosive mixture in some process reaction systems therefore, the system should be tested for air leaks and kept as tight as practical. 

Note System must be free of air leaks steam must be dry and condenser tubes clean. 

Comparatively small air leaks into the combustion spaces of a boiler can produce localized problems. All access opening seals and sight glasses and seals must be monitored to prevent this. 

Check pneumatics for air leaks and fully service compressor. 

Fig. 3.11 Conventional flasks for microdeterminations (a) air leak design (A) stopper design (c) filter paper for wrapping sample. Reproduced by permission from A. M. B. Macdonald, in Advances in Analytical Chemistry and Instrumentation, C. N. Reilly (Ed.), Vol. 4, Interscience, New York, 1965, p. 75.

Air leaks are another source of trouble in the MS. A simple method of leak detection is to squirt a small volume of acetone on flanges and other areas where leaks could occur. Caution is advised not to use this procedure near hot surfaces because of the flammability of acetone. A second way to test for small leaks is to tune the MS to m/z 40 and to use argon to test for leaks. The m/z 40 peak will increase if argon enters the source. Helium m/z 4) is a better choice, except when helium carrier gas is used in conjunction with the GC. A small stream of the gas is aimed at all seals where a leak can occur. If a leak is detected at a seal, it can sometimes be stopped by tightening the seal, but it is better to replace the seal than to overtighten it. 

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