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öf Hydraulk Engines.

wheel as F in Fig. i. of Flate VIII, having Ievers y, y,y,y on its up-right axle, to which horses may be joined for working the engine. Andif the wheel has three times as many cogs as the trundle has staves orrounds, the trundle and cranks will make three revolutions for everyone of the wheel: and as each crank will fetch a stroke in the time itgoes round, the three cranks will make nine strokes for every turn of thegreat wheel.

The cranks fhould be made of cast iron, becaufe that will not bend ;and they fhould each make an angle of 120 with both of the others,as at s, b,c ; which is (as it were) a view of their radii, in looking end- Plate xir.wife at the axis: and then there will be always one or other of them Fl S‘ 2>going downward,, which will pulh the watet forward with a continuedstream into the main pipe. For, when b is almost at its lowestsituation, and is therefore just; beginning to lose its action upon thepisto n which it moves, c is beginning to move downward, whichwill by its piston continue the propelling force upon the water: andwhen c is come down to the position of b, a will be in the positionof c.

The more perpendicularly the piston-rods move up and down in thepumps, the freer and bettet will their strokes be : but a little deviationfrom the perpendicular will not be material. Therefore, when thepump-rods D, E, and F go down into a deep well, they may bemoved directly by the cranks, as is done in a very good horfe-engineof this fort at the late Sir 'James Creed’s at Greenwic-h, which forces upwater about 64 feet from a well under ground, to a refervoir on thetop of his houfe. But when the cranks are only at a small heightabove the pumps, the pistons must be moved by vibrating Ievers, as inthe above engine at Blenheim : and the longer the Ievers are, the nearerwill the strokes be to a perpendicular.

Let us fuppofe, that in such an engine as Sir James Creed's, the A caicuiadongreat wheel is 12 feet diameter, the trundle 4 feet, and the radius or the s *i uan “length of each crank 9. inches, working a piston in Its pump. Let that may bethere be three pumps in all, and the bore of each pump be fcur inches b y. adiameter. Then, if the great wheel has three times as many cogs as ens ' ne-the trundle has staves, the trundle and cranks will go three times roundfor each revolution of the horses and wheel, and the three cranks willmake nine strokes of the pumps in that time, each stroke being 18inches (or double the length of the crank) in a four-inch bore. Letthe diameter of the horfe-walk be 18 feet, and the perpendicularheight to which the. water is raifed above the furface of the well be64 feet.

If