Machine drawing; a practical guide to the standard methods of graphical representation of machines, including complete detail drawings of a duplex pump and of a direct-current generator . tsmight be somewhat troublesome,it is shown in an enlarged sketchfor the students benefit, Chipping or filing strips finch high are left on the portedges, which must be true, inorder to finish them up easily. The three inner ports are for exhaust, the outer ones for admis-sion of steam. This five-ported cylinder is peculiar to the directacting steam pump, it being a device to effect the cushioning of
Machine drawing; a practical guide to the standard methods of graphical representation of machines, including complete detail drawings of a duplex pump and of a direct-current generator . tsmight be somewhat troublesome,it is shown in an enlarged sketchfor the students benefit, Chipping or filing strips finch high are left on the portedges, which must be true, inorder to finish them up easily. The three inner ports are for exhaust, the outer ones for admis-sion of steam. This five-ported cylinder is peculiar to the directacting steam pump, it being a device to effect the cushioning of thepiston at the end of the stroke, thus preventing the piston fromstriking the heads. This is necessary, since no positive limit ofmotion exists, as is the case in machines with crank and connectingrod. When the edge of the piston has passed the outer edge of theexhaust port, as shown in Fig. 121, the steam, which has been ex-hausting through port A, is confined in space B and port C, and,being compressed by the piston, acts like a spring to retard itsmotion. If the point P is properly determined for a given speed,the piston will always compress the steam just enough to cause it. Fig. 121. Enlarged Details of Steam Port MACHINE DRAWING 169 to stop at the end of the nominal stroke; in this case, J inch fromthe head. It is evident, however, that at different speeds the pistonwill have more or less power to compress the steam, and will notstop at the point desired. This causes the trouble of short stroke,and consequent inability to make the pump work to its full if we connect ports A and C by a small opening shown dottedat D, and control this opening by a plug valve operated by handfrom the outside, we can let a little steam leak by into port A, thusreducing the cushion and allowing full stroke. In order to avoid complicating the drawing, no cushion valvesare shown or required to be put on by the student. They are notcustomary in small pumps, but might advantageousl
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Keywords: ., bookcentury1900, bookdecade1910, bookpublis, booksubjectmachinery
