are to be joined. The purpose of dielectric fittings uniform  plastic  state,  joining  the  components is  to  curtail  galvanic  or  electrolytic  action.  The together,  and  then  allowing  the  two  surfaces  to most  common  dielectric  fittings  are  the  union, fuse into a homogeneous bond as the materials cool coupling,  and  bushing. to  room  temperature. Fittings  are  identified  by  the  sizes  of  pipe  that are connected to their openings. For example, a 3-  by  3-  by  1  1/2-in.  tee  is  one  that  has  two openings  for  a  3-in.  run  of  pipe  and  a  1  1/2-in. reduced outlet. If all openings are the same size, only  one  nominal  diameter  is  designated.  For example,  a  3-in.  tee  is  one  that  has  three  3-in. openings. Joints and Connections There are various methods of joining pipes for water distribution systems. Each method used is designed  to  withstand  internal  (hydrostatic) pressure in the pipe and normal soil loads if joints and connections are belowground. Some of these methods   produce   the   types   of   joints   and connections  described  below. FLARED AND SWEATED JOINTS.— These joints  are  generally  used  with  copper  pipe  and tubing.  The  end  of  a  copper  pipe  is  formed  into a  funnellike  shape  so  that  it  can  be  held  in  a threaded fitting when a line joint is being made. This method is called FLARING, and the result is  called  a  FLARED  JOINT.  A  SWEATED JOINT  is  made  with  soft  solder  instead  of  threads or  flares.  In  plumbing,  copper  pipe  or  tubing  is occasionally fused by heating with a gas flame and silver-aIloy filler metal called SILVER BLAZING (also   called   HARD   SOLDERING). SOLVENT  WELDED,  FUSION  WELDED, FILLET   WELDED,   THREADED,   AND FLANGED JOINTS.— These types of joints are common  to  plastic  pipes.  In  the  production  of a SOLVENT WELDED JOINT, a solvent cement with a primer is used. Before solvent is applied, the pipe and fitting must be thermally balanced (caused  to  have  similar  temperatures).  This process  should  not  be  undertaken  when  the temperature is below 40°F or above 90°F or when the pipes are exposed to direct sunlight. FUSION WELDED JOINTS are produced by the use of a gas- or an electric-heated welding tool. The process consists of simultaneously heating the meeting  surfaces  of  the  pipe  and  fitting  to  a FILLET WELDED JOINTS are made by the use of a uniform heat and pressure on the welding rod during application of the bead. This process can   also   be   applied   to   repair   leaks   in thermoplastics. In  plastic  pipes,  THREADED  JOINTS  are commonly  used  for  temporary  and  low-pressure piping   since   threading   reduces   the   pipe   wall thickness.   Only   certain   heavy   pipes   can   be threaded  with  a  special  strap  wrench.  Teflon  tape is often used for pipe joint compound when this method  of  joining  pipes  is  used. FLANGED JOINTS are extensively used for process   lines   that   are   dismantled   frequently. Plastic  pipes  are  joined  together  by  the  use  of plastic  flanges  with  soft  rubber  gaskets. BELL-AND-SPIGOT AND MECHANICAL JOINTS.—   These  types  of  joints  are  most commonly used with cast-iron pressure pipe and fittings for water mains. These service lines are joined by the use of lead, lead wool, or sometimes a  sulfur  compound.  Mechanical  joints  are  made with rubber sealing rings held in place by metal follower rings that are bolted to the pipe. These are designed to permit expansion and contraction of  the  pipe  without  injury  to  the  joints. THREADED   PIPE   JOINTS   are   commonly used  on  galvanized  steel,  galvanized  wrought iron, and   black-iron   pipe.   The   process includes  connecting  threaded  male  and  female ends.  Nontoxic  compounds  are  used  for  t  bread lubricant  on  water  pipes,  while  powdered  graphite and  oil  are  used  for  steam  pipes. Valves Valves are devices that are used to stop, start, or  regulate  the  flow  of  water  into,  through,  or from pipes. Essentially, valves consist of a body containing an opening and a means of closing the opening  with  a  valve  disk  or  plug  that  can  be tightly pressed against a seating surface around or   within   the   opening.   Many   different   valve designs are available; however, only the three most common  types  of  valves  will  be  discussed  here. They  are  the  gate,  check,  and  globe  valves. 8-6