As  the  load  is  lifted  and  begins  to  dump,  the required  force  becomes  less  and  less  until  the  load is  completely  dumped.  During  the  raise  cycle, pressurized fluid enters the cylinder through port A  (fig.  10-3)  and  acts  on  the  bottom  surface  of all three rams. Ram 1 has a larger surface area and, therefore, provides the greater force for the initial load, As ram 1 reaches the end of its stroke and the required force is decreased, ram 2 moves, providing  the  smaller  force  needed  to  continue raising the load. When ram 2 completes its stroke, a still smaller force is required. Ram 3 then moves outward to finish raising and dumping the load. Some  telescoping  ram-type  cylinders  are  of  the single-acting   type.   Like   the   single-acting   ram discussed previously, these telescoping ram-type cylinders are retracted by gravity or mechanical force.  Some  hydraulic  jacks  are  equipped  with telescoping   rams.   Such   jacks   are   used   to   lift vehicles with low clearances to the required height. Other types of telescoping cylinders, like the one illustrated in figure 10-3, are of the double- acting  type.  In  this  type,  fluid  pressure  is  used  for both the extension and retraction strokes. A four- way  directional  control  valve  is  commonly  used to control the operation of the double-acting type. Note the small passages in the walls of rams 1 and 2.  They  provide  a  path  for  fluid  to  flow  to  and from the chambers above the lips of rams 2 and 3. During the extension stroke, return fluid flows through  these  passages  and  out  of  the  cylinder through   port   B.   It   then   flows   through   the directional  control  valve  to  the  return  line  or reservoir. To  retract  the  rams,  fluid  under  pressure  is directed into the cylinder through port B and acts against the top surface areas of all three ram lips. This  forces  the  rams  to  the  retracted  position.  The displaced fluid from the opposite side of the rams flows out of the cylinder through port A, through the directional control valve to the return line or reservoir. Dual Rams A dual ram assembly consists of a single ram with a cylinder at either end (fig. 10-4). Fluid can be directed to either cylinder, forcing the ram to move  in  the  opposite  direction.  The  ram  is connected through mechanical linkage to the unit to  be  operated.  A  four-way  directional  control valve is commonly used to operate the dual ram. When  the  control  valve  is  positioned  to  direct  fluid under  pressure  to  one  of  the  cylinders  (let’s  say the left one), the ram is forced to the right. This Figure 10-4.-Dual ram actuating assembly. action  displaces  the  fluid  in  the  opposite  cylinder. The   displaced   fluid   flows   back   through   the directional  control  valve  to  the  return  line  or reservoir  in  hydraulic  systems  or  to  the atmosphere  in  pneumatic  systems. Dual  ram  actuating  assemblies  are  used  in steering systems of most ships. In some systems, one assembly is used to actuate the rudder in either direction; while in other systems, two assemblies are  used  for  the  same  purpose. PISTON-TYPE  CYLINDERS An  actuating  cylinder  in  which  the  cross- sectional area of the piston is less than one-half the  cross-sectional  area  of  the  movable  element is referred to as a piston-type cylinder. This type of cylinder is normally used for applications that require both push and pull functions. The piston- type  cylinder  is  the  most  common  type  used  in fluid  power  systems. The  essential  parts  of  a  piston-type  cylinder are a cylindrical barrel, a piston and rod, end caps, and suitable seals. The end caps are attached to the  ends  of  the  barrel.  These  end  caps  usually contain  the  fluid  ports.  The  end  cap  on  the  rod end  contains  a  hole  for  the  piston  rod  to  pass through.  Suitable  seals  are  used  between  the  hole and the piston rod to keep fluid from leaking out and  to  keep  dirt  and  other  contaminants  from entering the barrel. The opposite end cap of most cylinders  is  provided  with  a  fitting  for  securing the  actuating  cylinder  to  some  structure.  This  end cap  is  referred  to  as  the  anchor  end  cap. The piston rod may extend through either or both  ends  of  the  cylinder.  The  extended  end  of the  rod  is  normally  threaded  so  that  some  type of  mechanical  connector,  such  as  an  eyebolt  or a  clevis,  and  a  locknut  can  be  attached.  This threaded  connection  of  the  rod  and  mechanical connector  provides  for  adjustment  between  the rod and the unit to be actuated. After the correct 10-3