EXHAUSTING MACHINERY
489
by-pass and throttle governors shall be provided. On large works where a number of exhauster units are employed, tliere is no necessity for a by-pass governor, for, according to the make, exhauster sets are started up or shut oft and the whole of the governing can be done by steam regulation. On small and medium-sized works, however, where only duplicate machin.es are in use, a single exhauster has probably to deal with the maximum winter and minimum summer make. In this case the exliauster is usually installed to allow room for future extension ; consequently, with-out the by-pass governor it would have to run at an iaconveniently low speed when dealing with the minimum make. In such cases it is preferable, therefore, to supply a by-pass governor, which is adjusted from time to time according to the season, while the throttle governor Controls the speed of the engine according to the varying makes during the twenty-four ho ur s. Waller’s latest form of hydraulic governor is shown in Fig. 300.
The Lubrication of Exhausters
The lubrication of the exhauster is a point requir-ing very careful attention, for endless trouble may iollow the use of unsuitable oils. For most purposes the best lubricant is a mixture of
refined creosote and mineral 3OO._Walleb>s hydbaulic Govebnob.
oil—one part of the former
to three of the latter. A heavy oil should always be used, also an oil that will act as a solvent for the tar, such, as a good mineral oil, rather than a vegetable oil which. will thicken with the tar. The temperature of the gas, the quantity of suspended tar, and whether the gas is clean or foul, are all important factors from the point of view of lubrication ; and experience is, perhaps, the most reliable guide. When the exliausters are preceded by tar extractors it will be found preferable to use an ordinary engine oil of good quality. The tar vesicles present in the gas possess very important properties in relation to the lubrication of the exhauster, and it is