SEGMENTED   SOCKET,   RING   AND BAND ATTACHED.— The segmented, ring and band  attached  socket  consists  of  three  or  more segments.  As  with  the  bolt-together  segments,  the segments, ring and band are put on the hose after insertion of the nipple. A special tool is required to  compress  the  segments. SEGMENTED SOCKET, RING AND BOLT ATTACHED.—  The  segmented,  ring  and  bolt attached   socket   consists   of   three   or   more segments.  As  with  other  segmented  socket-type fittings,  the  segments,  ring,  and  nuts  and  bolts are put on the hose after insertion of the nipple. SOLID   SOCKET,   PERMANENTLY ATTACHED.—   This  type  of  socket  is  perma- nently  attached  to  the  hose  by  crimping  or swaging.  It  is  not  reusable  and  is  only  found on  hose  assemblies  where  operating  conditions preclude  the  use  of  other  fitting  types.  Hose assemblies with this type of fitting attachment are purchased as complete hose assemblies from the manufacturer. QUICK-DISCONNECT   COUPLINGS Self-sealing,  quick-disconnect  couplings  are used  at  various  points  in  many  fluid  power systems.  These  couplings  are  installed  at  locations where  frequent  uncoupling  of  the  lines  is  required for   inspection,   test,   and   maintenance.   Quick- disconnect  couplings  are  also  commonly  used  in pneumatic systems to connect sections of air hose and  to  connect  tools  to  the  air  pressure  lines.  This provides  a  convenient  method  of  attaching  and detaching  tools  and  sections  of  lines  without  losing pressure. Quick-disconnect  couplings  provide  a  means for quickly disconnecting a line without the loss of  fluid  from  the  system  or  the  entrance  of foreign matter into the system. Several types of quick-disconnect  couplings  have  been  designed  for use  in  fluid  power  systems.  Figure  5-23  illustrates Figure 5-23.—Quick-disconnect coupling for air lines. a coupling that is used with portable pneumatic tools.  The  male  section  is  connected  to  the  tool or  to  the  line  leading  from  the  tool.  The  female section,  which  contains  the  shutoff  valve,  is installed   in   the   pneumatic   line   leading   from the  pressure  source.  These  connectors  can  be separated or connected by very little effort on the part  of  the  operator. The  most  common  quick-disconnect  coupling for hydraulic systems consists of two parts, held together  by  a  union  nut.  Each  part  contains  a valve  which  is  held  open  when  the  coupling  is connected,  allowing  fluid  to  flow  in  either direction   through   the   coupling.   When   the coupling  is  disconnected,  a  spring  in  each  part closes the valve, preventing the loss of fluid and entrance  of  foreign  matter. MANIFOLDS Some fluid power systems are equipped with manifolds  in  the  pressure  supply  and/or  return lines.   A   manifold   is   a   fluid   conductor   that provides   multiple   connection   ports.   Manifolds eliminate  piping,  reduce  joints,  which  are  often a  source  of  leakage,  and  conserve  space.  For example, manifolds may be used in systems that contain  several  subsystems.  One  common  line connects  the  pump  to  the  manifold.  There  are outlet  ports  in  the  manifold  to  provide  con- nections  to  each  subsystem.  A  similar  manifold may be used in the return system. Lines from the control valves of the subsystem connect to the inlet ports  of  the  manifold,  where  the  fluid  combines into   one   outlet   line   to   the   reservoir.   Some manifolds  are  equipped  with  the  check  valves, relief  valves,  filters,  and  so  on,  required  for  the system.  In  some  cases,  the  control  valves  are mounted on the manifold in such a manner that the ports of the valves are connected directly to the  manifold. Manifolds  are  usually  one  of  three  types— sandwich,  cast,  or  drilled.  The  sandwich  type  is constructed  of  three  or  more  flat  plates.  The center plate (or plates) is machined for passages, and  the  required  inlet  and  outlet  ports  are  drilled into the outer plates. The plates are then bonded together  to  provide  a  leakproof  assembly.  The  cast type  of  manifold  is  designed  with  cast  passages and drilled ports. The casting may be iron, steel, bronze,  or  aluminum,  depending  upon  the  type of system and fluid medium. In the drilled type of manifold, all ports and passages are drilled in a  block  of  metal. 5-19