1174

THEORY AND PRACTICE OF ENGINEERING.

Book II.

: not regular, whilst thethat part of the rod of

piston, and consequently the discharge of water through the pipepump with two pistons causes it to flow in a continual stream :the lower piston is shown at the side of the figure.

In Taylor's Sucking Pump> the piston rods have racks at their upper parts, working on theopposite sides of a pinion, and are kept to their proper position by friction rollers : a pumpof this description, with a bore of 7 inches, will lift a ton of water 24 feet high in a minute,when worked by ten men,five on each side. Thereare three kinds of valvesemployed; the first is aspheric segment, w’hichslides up and down on thepiston-rod, and is carrieddown by its own weight;the second is a pendu-lum valve ; and the othera globe which is raisedby the rising water, andfalls again by its ownweight.

Franklin's Double-Pis-ton Pump , with a sectionthrough the cylinder.

When the handle or leveris raised, the upper pistonpressed down, the lowerpiston elevated, and itsvalves shut, the water isforced through the upperpiston and the discharg-ing pipe. When thehandle is pressed down,the upper piston riseswith its valves closed, andthe water in its ascent isforced through the dis-charging pipe: at thesame time, the lower pis-ton descends, by which action the valves are opened, and a freshsupply of water is obtained: with a 6-inch stroke, a quantityof water equal to twelve inches of the cylinder is discharged:whatever the length of stroke, the quantity of water supplied isdoubled.

Stephen's Forcing Pump. — To the handle is attached a woodenrod of several lengths, united by iron joints, and capped with ironforks firmly riveted. The bucket works a brass tube, and thetop of the barrel is covered with a metal lid, which has a stuffing-box in the centre, to receive the metal cylindrical part of the pump-rod, to the lower extremity of which the bucket is fixed. Themetal lid consists of a ring screwed to a wooden barrel by fivescrew’ bolts. The forcing pipe may be made of wood, or fromcrooked timber.

The ordinary forcing-pump does not furnish an intermittingstream of water, but this effect is very simply attained by theaddition of an air-vessel, fitted upon the side of the main or risingpipe of the forcing-pump. The action of these air-vessels may bethus explained: suppose the pump to have received water abovethe valve, a part of which will get into the vessel and compressthe air within it, udth a force proportional to the height of thecolumn in the main pipe; when, by the next stroke, the pistondraws up more w f ater, and it stands higher in the main, the air-vessel is more powerfully compressed. After the water is liftedto the point at which it Ls discharged, the air in the vessel becomesso much compressed, that it balances the whole height of thecolumn above it. If the opening through which the water flotfsat the top of the main were sufficiently large permit the waterto issue with the same velocity as that of the piston, it would flow

Fig. 1783. taylor’s pump.

Fig. 1784. franklin’s double-piston.

Fig. 17*. r >. STEPHBN’SFORCING-PUMP.