Modern Gasworks Practice

EXHAUSTING MACHINERY 491 vided with a hole for injecting oil. When possible, a continuous flow of oil, as given, by one of the mechanical lubricators, should always be arranged for, this being very much more effective than an intermittent supply. The distribution must, moreover, be uniform, as a dry portion, where contact occurs quickly results in heating and subsequent erosion of the surfaces. Water as a Lubricant The scarcity and high price of ordinary lubricating oils during the war led to an. attempt to use water for the purpose. The practice has been adopted with. considerable success in France,1 where it has been shown that the principle is entirely satisfactory so long as the water employed is chemically pure and free from sus-pended matter. The water may be supplied through ordinary drip-feed lubricators, or by means of a small pump. The rate of flow should be from 90 to 100 drops per minute for an exhauster having a capacity of about 200,000 cubic feet per day, and it is stated that if the machine is to stand idle for any length of time a small quantity of oil should be admitted in order to prevent rusting. Guillet states that instead of water it is preferable to use ammoniacal liquor, since a hard water, under the action of ammonia and carbon dioxide in the gas, forms a deposit which may give rise to trouble. With ammoniacal liquor no derangement occurs ; in fact the interior surface of the exhauster takes a high polish. The following results were obtained from an electrically driven exhauster when lubricated by oil and water respectively :— Oil. Water. Power absorbed (watt hours)_________________________ 7,500 .. 5,000 Temperature _______________________________________........ 30° C. .. 20° C. Precautions against Stoppages Owing to the seizure of a bearing. the slipping of a beit, the burning out of a fuse, or some other unlooked-for cause, an exhauster is liable to pull-up at short notice. This, of course, should not occur if the machine is properly attended to ; but, nevertheless, it is an emergency which must always be provided for. In addition to duplicate plant some means should be provided for guarding against the undue pressure which would otherwise be thrown upon the retorts and the apparatus between them and the exhauster. A usual method is to insert in a by-pass pipe connecting miet and outlet a safety flap-valve such as that shown in Fig. 302. In the ordinary way the outlet pressure holds the valve against its seatings, but should the exhauster stop the inlet pressure will, after a time, exceed that on the outlet, so that the valve is forced open, giving a free way for the gas. It will be realized, however. that only temporary relief is afiorded before the pressure of the whole apparatus will be thrown on the retorts. The flap valves are usually fitted with a handle, as shown, so that they may occasionally be jarred in. Order to ensure that sticking will not occur. On the rare occasions when the exhausting plant breaks down it is unreason- 1 J. des Usines d Gaz, Jan. 20, 1918.