Figure 10-10.-Hydraulic press.1-pound effort without sacrificing distance. You mustapply the 1-pound effort through a much greaterdistance than the 10-pound force will move. To raise the10-pound weight a distance of 1 foot, you must applythe 1-pound effort through what distance? Remember,if you neglect friction, the work done on any machineequals the work done by that machine. Use the workformula to find how far the smaller piston will have tomove.Work input = Work outputFlxDl=F~xD2By substitutinglXD1=lOX1you find thatD] = 10 feetThe smaller piston will have to move a distance of10 feet to raise the 10-pound load 1 foot. It looks thenas though the smaller cylinder would have to be at least10 feet long—and that wouldn’t be practical. Inaddition, it isn’t necessary if you put a valve in thesystem.The hydraulic press in figure 10-10 contains a valve.As the small piston moves down, it forces the fluid pastcheck valve A into the large cylinder. As soon as thesmall piston moves upward, it removes the pressure tothe right of check valve A. The pressure of the fluid onthe check valve spring below the large piston helps forcethat valve shut. The liquid that has passed through thevalve opening on the down stroke of the small piston istrapped in the large cylinder.The small piston rises on the upstroke until itsbottom passes the opening to the fluid reservoir. Morefluid is sucked past check valve B and into the smallcylinder. The next downstroke forces this new charge offluid out of the small cylinder past the check valve intothe large cylinder. This process repeats stroke by strokeuntil enough fluid has been forced into the large cylinderto raise the large piston the required distance of 1 foot.The force has been applied through a distance of 10 feeton the pump handle. However, it was done through aseries of relatively short strokes, the total of the strokesbeing equal to 10 feet.Maybe you’re beginning to wonder how the largepiston gets back down after the process is finished. Thefluid can’t run back past check valve B-that’s obvious,Therefore, you lower the piston by letting the oil flowback into the reservoir through a return line. Notice thata simple globe valve is in this line. When the globe valveopens, the fluid flows back into the reservoir. Of course,this valve is shut while the pump is in operation.Aiding the HelmsmanYou’ve probably seen the helmsman swing a shipweighing thousands of tons almost as easily as you turnyour car. No, helmsmen are not superhuman. Theycontrol the ship with machines. Many of these machinesare hydraulic.There are several types of hydraulic and electro-hydraulic steering mechanisms. The simplified diagram10-7
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