490
MODERN GASWORKS PRACTICE
important to ensure that the necessary fluidity of the tar is maintamed. Dr. Carpenter has emphasized the value of the tar present by showing that, when the ex-hausters are placed prior to the condensers in sequence, no lubricating oil whatever is necessary.
Special apparatus for the lubrication of exhausters is now nearly always em-ployed. The forms most generally made use of are
(a) Ordinary self-contained drip-feed.
(b) Pressure system, embodying the use of a reservoir from which the oil is expelled by the pressure of gas at the outlet of the exhauster.
(c) Mechanical appliances, such as miniature pumps driven by gearing or belting from the exhauster shaft.
The several points at which an exhauster should be lubricated depend largely upon the type of the machine. Taking, however, as an instan.ee one of the three-or four-blade types such as Waller’s (Fig. 292), it will be seen that the inner drum is supported and rotates in recessed covers, therefore lubrication is required at these points. The hinges upon which. the blades are carried upon the central spindle ara lubricated by means of an oil hole provided by boring through the whole length. of the spindle, oil being forced through this duet by an automatic or hånd. pump. In the case of the old pattern two-blade Beale exhauster the inner drum is sup-ported by the shaft, which is carried in out-side bearings ; these require lubrication, as do the segments which rotate in grooves in the covers. The latest pattem Beale machine is provided with a recessed back cover which requires lubrication, the driving shaft is supported by an outer bearing which must also be lubricated, whilst the steel spindle supporting the centre block upon which the blades rotate is pro-