Handbook of Ship Calculations, Construction and Operation; A Book of Reference for Shipowners, Ship Officers, Ship and Engine Draughtsmen, Marine Engi

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 Excerpt: ...= edge of valve extends over edge of port on exhaust side In Fig. 68, A B steam lead = distance port is uncovered to steam C D exhaust lead = distance port is uncovered for exhaust. Valve Travel.--The travel of a valve is equal to (steam lap + port opening) X 2. The following data is of a cargo steamer 27 X 46 X 76 with an engine--, 2360 i. h. p., high pressure receiver 180 lb., intermediate 55 lb., low pressure 16 lb., r. p. m. 63, vacuum 27 ins., speed 11.2 knots. Valve Mechanism.--The most satisfactory valve mechanism for vertical marine steam engines is the Stephenson. With it the direction of rotation of the engine may be changed at will, and the point of cut-off varied by varying the travel of the valve. The Stephenson valve mechanism or link motion consists of two eccentrics, viz., ahead and astern, with a link connecting the ends of the eccentric rods that are fastened to the eccentric straps on the engine shaft, so that by varying the position of the link the valve stem may be put in direct connection with either eccentric or may be given a movement controlled partly by one eccentric and partly by the other. When the link is moved by suitable levers into a position such that the block to which the valve stem is attached is at either end of the link, the valve receives its maximum travel and when the link is in mid-position the travel is the least and the cut-off takes place early in the stroke. The expression "open and crossed eccentric rods" is understood to mean the position of the eccentric rods when the crank is on the bottom center, as in running the rods open and cross each other alternately. For slide valves or outside steam piston valves the rods are usually arranged as open, but with inside steam piston valves the rods are fitted...