Modern Gasworks Practice

486 MODERN GASWORKS PRACTICE 296. The inlet and outlet of the exhauster are connected by a short length of pipe in which an ordinary butterfly valve, attached to a quadrant (Fig. 297) is inserted. The quadrant is then attached by a chain and lever to the bell of a small gasholder which is connected by a small service pipe (F) to the inlet main of the exhauster. Fig. 297.— Quadrant and Valve. The quantity of gas coming away from the retort liouse varies to some considerable extent at different, periods of the day. Accordingly, the intensity of vacuum produced will also vary in ratio to the amount passing if the speed of the exhauster is permitted to remain constant. In this type of governing tlie speed of the engine is maintained. fairly constant, and at a sufficient velocity to take the maximum quantity of gas coming from the retorts. When the quantity passing along the foul main undergoes reduction the vacuum becomes momentarily increased;