Now screw up the stuffing-box nut (having previously removed the packing), then move the valve and stem so that the small port at right of valve will be open 1/16 inch and make a scratch upon the stem close to stuffing-box nut. The valve should then be moved in the opposite direction to open the other small port 1/16 inch and make a second scratch upon the valve stem next to stuffing-box nut. Prepare joint and replace steam chest on cylinder. To square the valve, slacken the screw in crosshead and move the latter to the end of stroke with edge of crosshead flush with the end of guide, then set the valve stem so that the first scratch is flush with the face of nut, same as when the scratch was made. Tighten screw in set screw under valve rod dog and move the crosshead to the opposite end of stroke, and note the position of second scratch. If it does not come to the position in which it was made, _split the difference by slackening the set screw under valve rod dog and move the valve rod to equalize the travel of valve_. In replacing steam chest on cylinder, cover the opening with a thin board, or piece of sheet iron, before turning it over to prevent the valve from dropping out of place. This slide valve has a fixed travel and _the process of setting is precisely the same as for that upon a steam engine with a plain slide valve_. SMITH-VAILE SINGLE PUMP. [Illustration: FIGS. 298, 299.] The accompanying sectional view of steam end of the “Smith-Vaile” exhibits some very novel features. So far as the piston and cylinder in this pump are concerned they are not unlike the average first class pump, but with this difference. It has only one set of cored ports, B, B. The supplemental ports, C, C, are drilled. The main valve, A, is a slide and is moved by a valve piston, D. Almost all the valve pistons as now made are simply plugs turned accurately to fit the holes in the chest and without any means of adjustment to compensate for wear. After these valve pistons become worn they have to be replaced with new ones, but there is a period between the time when the valve piston becomes so leaky as to render the action of the pump uncertain and the time when the worn valve is replaced by a new one that the pump is very wasteful of steam.