Figure 3-7.-Valves. and E₁ = 900 = 112/5 pounds         8 Slim,  the  smart  sailor,  has  to  lift  only  112.5 pounds.    There’s    a    sailor    who    really    puts    his knowledge to work. THE COUPLE Take  a  look  at  figure  3-6.  It’s  another  capstan- turning   situation.   To   increase   an   effective   effort, place  a  second  capstan  bar  opposite  the  first  and another  sailor  can  apply  a  force  on  the  second  bar. The   two   sailors   in   figure   3-6   will   apparently   be pushing  in  opposite  directions.  Since  they  are  on opposite  sides  of  the  axle,  they  are  actually  causing rotation in the same direction. If the two  sailors  are pushing with equal force, the moment of force is twice as  great  as  if  only  one  sailor  were  pushing.  This arrangement is known technically as a couple. You will see that the couple is a special example of the wheel and axle. The moment of force is equal to the product of the total distance (L_n between the two points  and  the  force  (E₁)  applied  by  one  sailor.  The equation for the couple may be written E₁ x L_T = E₂ x L₂ APPLICATIONS AFLOAT AND ASHORE A  trip  to  the  engine  room  important  the  wheel and  axle  makes  you   realize  how  is  on  the  modern ship. Figure 3-8.—A simple torque wrench. Everywhere you look you see wheels of all  sizes and shapes. We use most of them to open and close valves quickly. One common type of valve is shown in figure 3-7.  Turning  the  wheel  causes  the  threaded  stem  to rise  and  open  the  valve.  Since  the  valve  must  close watertight, airtight, or steamtight, all the parts must fit snugly. To move the stem on most valves without the aid of the wheel would be impossible. The wheel gives you the necessary mechanical advantage. You’ve  handled  enough  wrenches  to  know  that the longer the handle, the tighter you can turn a nut. Actually, a wrench is a wheel-and-axle machine. You can consider the handle as one spoke of a wheel and the place where you take hold of the handle as a point on the rim. You can compare the nut that holds in the jaws of the wrench to the axle. You know that you can turn a nut too tight and strip the threads or cause internal parts to seize. This is   especially   true   when   you   are   taking   up   on bearings. To make the proper adjustment, you use a torque  wrench.  There  are  several  types.  Figure  3-8 shows you one that is very simple. When you pull on the  handle,  its  shaft  bends.  The  rod  fixed  on  the pointer does not bend. The pointer shows on the scale the torque, or moment of force, that you are exerting. The   scale   indicates   pounds,   although   it   is   really measuring  foot-pounds  to  torque.  If  the  nut  is  to  be tightened by a moment of 90 ft-1b, you pull until the pointer  is  opposite  the  number  90  on  the  scale.  The servicing  or  repair  manual  on  an  engine  or  piece  of machinery  tells  you  what  the  torque—or  moment  of force—should be on each set of nuts or bolt. The  gun  pointer  uses  a  couple  to  elevate  and depress   the   gun barrel.   He   cranks   away   at   a handwheel  that  has  two  handles.  The   right-hand handle  is  on  the  opposite  side  of  the  axle  from  the left-hand handle—180° apart. 3-5