360 KINEMATICS OF MACHINERY.
link c, otherwise the arrangement is very similar to that of Knott's pump. We have again (F) d, b, and the crank a is again the driving-link. The higher pairing used between d and b on account of the omission of c is that of Fig. 270, it is exactly the same therefore as that employed by Lamb in the machines shown in PL XV. The pressures commonly required in blowing machines are so small that the closure at 3 is quite sufficient, and for the same reason the disadvantage of the momentary communication between the suction and delivery pipes when the crank is at its upper centre is greatly reduced.* The relation between the machine before us and that of Lamb (PL XV. Fig. 1) merits closer examination. We find that the inner cylinder d of Lamb's engine, with its prismatic plate 3', corresponds to the piston of the machine before us, and the revolving annular piston of the former to the chamber of the latter, and this again conditions their respective double and single action. Herr Wedding remarks that by suitably forming the upper portion of b and d we could make them into a second chamber and piston respectively, and that the latter would be in its most advantageous positions when the first piston was in its worst, i.e., at the upper centre, and vice versd. Here again there is an analogy with Lamb's machine, where the actions on the two sides of the annular piston have the same relation to each other.
Once more looking back from the two last machines to Fig." 1, PL XIV, we cannot wonder that it has only been after the most careful and searching analysis that we have been able to recognise the turned connecting rod of the common steam-engine in the peculiar looking chamber b, or its framing in the club-shaped piston d.
82.
Chamber-crank Trains from the Turning Block. Plates XVIII. to XXII.
No one of the crank mechanisms has been turned to account as a rotary engine or pump in so many different ways as the turning
- Two 6 horse-power machines of "Wedding, used in the Spandau Artillery
Works, apparently worked well. (The pistons here were made of wood, the plate at d of thin boards.) Lately, however, both machines have been replaced by common fans, because the diminution of pressure occurring as the crank passed the upper centres was found to affect the smiths' fires, R,
