386 MODERN STEAM PRACTICE . for double - ported valves , that is to say , there are two steam passages at each end , and one central passage , in communication with the condenser . The joints should be placed metal to metal , all planed or surfaced in the boring lathe , and the rubbing surfaces… … the front end of the cylinder a central manhole must be left , for the boring bar to pass through ; with single piston rods there is a small cover with stuffing box and gland , but with double or more piston rods a plain cover is fitted ; holes are also left in the front end of the cylinder for the…
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