482
MODERN GASWORKS PRACTICE
of exhauster is now made for
working against pressures up to 10 1b. per square inch.
Typical examples of the multiple exhauster are shown in Figs. 291 and 292. The outer drum is bored truly cylindrical, whilst the internal drum (which is about two-thirds the diameter of the
external casing) is fitted with three or four small roils which.
Fia/293.—Walleb Exhattster with End-flate bemoved. are slotted out to take the blades, and oscillate in the bearings according to the movement of the blades. The ends of the roils project beyond the width of the inner drum and are supported in bored recesses in the end covers. The blades are hinged on a sliaft which is central with the outer drum, and which extends the whole length of the cylinder and is supported in a deep boss on the back cover, and secured by a nut. To facilitate lubrication this spindle is bored down its entire length. The driving shaft is cast on to the inner drum and projects through a giand and stuffing box in the inner cover. In order to reduce the losses by “ slip ” the tips of the blades are fitted with T-shaped strips which. are forced against the inner periphery of the drum by spiral springs. The con-
struction of fliese exhausters will be readily seen by réferring to Figs. 293 and 294.
The number of blades fitted bears some relation to the capacity of the exhauster ; and, in general, all machines dealing with. less than 5,000 cubic feet per hour are fitted with two blades ; all above this capacity and up to 25,000 cubic feet per hour are of the three-blade type; whilst four blades are fitted for sizes larger than this. The smallest rotary exhausters made are 3 inches internal diameter and 3 inches long, but these are seldom used for anything beyond adding air to the dry purifiers or for com-pressing purposes. They are of the two-blade type, running at about 500 revolutions per mimrte, and having a gross output of about 115 cubic feet per hour. The largest exhausters manufactured, which are chiefly employed on coke-oven works, have a capacity of about 450,000 cubic feet per hour,
Frø. 294.—Exhauster, showing Inner Druji pulled away from Blades.