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HYDRAULICS


used, and the .tendency of relay governors to hunt .must be overcome. In the Niaga.ra'Falls Power House No. x, each turbine has a very sensitive centrifugal governor acting on a ratchet relay. The governor puts into gear one or other of-two ratchets driven by the turbine itself. According as one or the other ratchet is in gear the sluices are raised or lowered. By a subsidiary arrangement the ratchets are gradually put out of gear unless the governor puts them in gear again, and this prevents- the over correction of the speed from the lag in. the action of the governor. In the Niagara Power House -No. 2, the relay 'is an hydraulic relay similar in principle, but rather more complicated in arrangement, to that shown in figi 2o6, which is a' governor used for the 12 50 h.p. turbines at Lyons. The sensitive governor G opens a valve and puts into action a plunger driven 'by oil pressure from an oil reservoir. As the plunger moves forward it gradually closes the oil admission valve by lowering the fulcrum end f of the valve lever which rests on awedge watt ached to the plunger. If the speed is still too high, the governor reopens the valve. In the case of the Niagaraturbines the oil pressure is rzoo lb per sq. in. One millimetre of movement of the governor sleeve completely opens the relay valve, and the relay plunger exerts a force of 5o tons. Thesluices can be completely opened or shut in twelve seconds. The ordinary variation of speed of the turbine with' varying load does not exceed 1 %. If all the load is thrown off, the momentary variation of speed is not more than 5%. To prevent hydraulic shock in the supply pipes, a relief valve is provided which opens if the pressure is in excess of that due to theehead. - "5 . § 205. The Hydraulic Ram.-The hydraulic ram is an arrangement by which a quantity of water falling a distance 'h forces a portion of the water to rise to a height hr, greater than h. It consists of a supply reservoir (A, fig. 207), into which the water enters from some natural stream. A pipe s of considerable length conducts the water to a lower level, where it is discharged intermittently through a self-acting pulsating valveyat d. The supply pipe s may be htted with a flap valve for stopping the ram, and this is attached in some .cases to afloat, so that the ram starts and stops itself automatically; according the supply cistern fills or empties. The lower fioatis just“suH'leient=.to keep open the Hap after it has been raised the action of the upper float. The length of chain is adjusted so that the upper float opens the flap when the level in the cistern is at the desired height. If the water-level falls below the lower iloat the Hap closes. The pipe .r should be as long and as straight as possible, and as it is subjected to considerable pressure from the sudden arrest of the motion of the water, it must be strong and strongly

4 PUMPS this opens an aperture fin. in'diameter, made in a brass screw plug b., The hole is reduced to 115 in. in diameter at the outer end of the plug and is closedby a small valve opening inwards. Through this, during the rebound after each stroke of the ram, a small quantity of air is sucked in which keeps the air vessel supplied with its elastic cushion of air. During the recoil aiteria sudden closing of the valve d, the pressure below it is diminished and the valve opens, permitting outflow. In consequence of the .flow through this valve, the water in the supply pipe acquires a gradually increasing velocity. The upward How of the water, towards the valve d, increases the pressure tending to lift the valve, and at last, 2 if the valve is not too » I ®@&¥s¥sog

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s - S heavy, lifts and closes it. The forward mo» mentum of the column in- the “supply pipe being destroyed by the ' 7: stoppage of the flow, the water exerts a | § s rt S P Mm, f pressure at the end of the pipe sufficient to open the delivery valve o, and to cause ~ <' " * if " -if~'il¥'; li; 5 a portion of the water M to flow into the air vessel. As the water in the supply, pipe comes to"rest and iiecoils, thelvalve rl opens again and the » Part of the energy of the descending

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I ~ F IG. 208.operation is- repeated. coiumn is employed in compressing the air at the end of the supply pipe and expanding the pipe itself. This causes a recoil of the water which momentarily diminishes the pressure in the pipe below the pressure due to the statical head. ~ This assists in opening the valve d. The recoil of the water is sufficiently great to enable a pump to be attached to the ram body instead of the direct rising pipe. With this arrangement a ram working with muddy water may be employed to raise clear spring water. Instead of lifting the delivery valve as in the ordinary ram, the momentum of the column drives a sliding or elastic piston, and the recoil brings it back. This piston lifts and forces A alternately the clear water through ordinary 737 ze.. A " pump valves' PUMPS T °' - - T. “ ' ! f A"' - .

-'L-E-I.-I~'I-eiei- ~ ' - 4 ' , y § 206. The different classes of pumps correlfii-ff-';-f-;-f-

-' Q ' - spond almost exactly to the different classes -: -::;:'::'; ' f ' of water motors, although the mechanical 4;3-'-'- -'- -'- - -°~'3 ' " 1” 9 ~ =. ' details of the construction are somewhat ~ - - - * - ~ -; - /711.1 » . ¢ 61|-~ d-5 t Th 1 d . ~ a 7/T ywy/7: X 1 |;, Q A 1 eren ey are proper y reverse - water 8 // Flo. 207. jointed. a is an air vessel, and e the delivery leading to the reservoir at a higher level than A, into which water is to be pumped. Fig. 2o8 shows in section the construction of the ram itself. d is the pulsating discharge valve already mentioned, which opens inwards and downwards. The stroke of the valve is regulated by the cotter through the spindle, under which are washers by which the amount of fall can be regulated. At o is a delivery valve, opening outwards, which is often a ball valve but sometimes a flap-Valve. The water which is pumped passes through this valve into the air vessel a, from which it flows by the delivery pipe in a regular stream into the cistern to which the water is to be raised., In the vertical chamber behind the outer valve a small air vessel is formed, and' into f » | i motors. Ordinary reciprocating pumps Corre=. ¥ s

sg . /ll! spond to water-pressure engines. Chain and bucket pumps are in principle similar to water wheels in which the water acts by weight. Scoop wheels are similar to undershot water wheels, and centrifugal pumps to turbines. Reciprocating Pumps are single or double acting, and diiieg from water-pressure engines in that the valves are moved by the 'water instead of by automatic machinery. ' They may be classed thus:-~ ' tr. Lift Pumps.~Thc water drawn through a foot valve on the ascent of the pump bucket is forced through the bucket valve when it descends, and lifted by the bucket when it reascends. Such pumps- give an intermittent discharge. 2. Plemger or Force Pumps, in which the water drawn through the foot valveis displaced by the descent of a solid plunger, and

forced through a delivery valve. They have the advantage that