. American engineer and railroad journal . e. Themachine weighs about 1,400 pounds. To give some slight idea ofthe range of work for which it is intended several illustrationsare presented showing various operations on the No. 2 machine. AMERICAN SEMI-PLUG PISTON VALVE. The valve which is shown in the accompanying illustration iscalled a semi-plug piston valve because when drifting, or atany time with the steam shut off, it acts like a snap ring valve,that is, the packing rings are expansible and adjust themselves tothe valve chamber, but, when steam is turned on, it becomes aplug valve due to
. American engineer and railroad journal . e. Themachine weighs about 1,400 pounds. To give some slight idea ofthe range of work for which it is intended several illustrationsare presented showing various operations on the No. 2 machine. AMERICAN SEMI-PLUG PISTON VALVE. The valve which is shown in the accompanying illustration iscalled a semi-plug piston valve because when drifting, or atany time with the steam shut off, it acts like a snap ring valve,that is, the packing rings are expansible and adjust themselves tothe valve chamber, but, when steam is turned on, it becomes aplug valve due to the pressure acting on the wedges, as will beexplained below, and locking the snap rings at a fixed diameter. It is, of course, of great importance for securing the best servicefrom piston valves to have the cages perfectly true, and this con-dition would be best maintained by a plug valve. It is also ofimportance, for a satisfactory valve, to prevent lateral wearwhich will allow steam to blow around and underneath the rings. - E££S£3. It is for the purpose of fulfilling these requirements that thisvalve has been designed. Referring to the sectional view, it will be seen that the pack-ing consists of two snap rings (1) which have straight outsidefaces fitting against the straight wall of the follower and inner faces of the snap rings, however, are beveled. Insideof these are a pair of rings, (2) which are called wall are uncut, non-expansible, steel rings and are beveled atdifferent angles on the two sides, as shown. Between these fitsan expansible ring called a wedge ring (4). An expansible ring,(3) with grooves which forms the actual packing and bears onthe cage, fits between and interlocks with the snap rings. Thisring is wide enough to carry the snap rings across the port whendrifting, and it also acts to keep them parallel with each other. The operation of this packing is as follows: When steam isturned on, with an internal admission valve, it ent
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
