TM 1-1500-204-23-9 CHAPTER 5 PNEUMATIC TOOLS 5-1.  Pneumatic Tools.  Pneumatic tools look much the same     as     electric     tools,     but     they     are     driven     by compressed  air.    When  some  sort  of  air  compressor  is available in the field, these tools can be used for a vast variety of jobs that otherwise would be impossible to do or would take too long to do by hand. 5-2.        Safety    Precautions.        When     operating     or maintaining    air-driven    tools,    observe    the    following precautions to prevent injury to personnel: a. Inspect the air hose for cracks or other defects. Replace the hose if defects are found. b. Before  connecting  an  air  hose  to  an  air  outlet, open    the    shutoff    valve    momentarily    to    expel    any condensation. c. Never point the hose at another person. d. Stop   the   flow   of   air   to   a   pneumatic   tool   by closing the shutoff valve before connecting, disconnecting, adjusting, or repairing the tool. e. Always wear eye protection when using pneumatic tools. 5-3. Paint Guns.  The use of a paint gun permits a fast and effective means of applying paint. a. Description.  Figure 5-1 shows the basic parts of a  typical  paint  gun.    Though  the  specific  locations  of some  parts  may  differ  from  type  to  type,  the  guns  are generally   the   same   and   the   parts   serve   the   same purpose. b. Operation.          The     spray     gun     operates     on compressed  air  supplied  from  a  compressor.    The  flow of paint, is controlled by a needle valve when the trigger on the spray gun is actuated. c. Use.    The  correct  use  of  a  paint  gun  involves setting    the    spray    pattern,    painting    at    the    correct distance, and using the correct technique in the stroke. (1) Setting   the   spray   pattern.      The   spray pattern  is  variable  from  round  to  a  vertical,  flat,  oval pattern, with all patterns in between, as shown in figure 5-2.    The  vertical  fan-shaped  pattern  gives  maximum coverage as the gun is moved back and forth parallel to the  surface  being  painted.    The  fan  is  vertical  because the   wings   on   the   nozzle   are   horizontal,   as   shown   in figure  5-3.    To  adjust  the  spray  pattern  from  circular  to fan, proceed as follows (see figure 5-4): (a) To  adjust  the  spray  width,  turn  the spray width adjustment right for round, and left for fan. NOTE As  the  width  of  the  spray  is  increased, more  material  must  be  allowed  to  pass through   the   gun   to   achieve   the   same coverage on the increased area. (b) To increase or decrease the amount of   material,   turn   the   material   control   screw   right   to decrease flow, and left to increase flow. (2) Distance for spraying.    Depending  on  the desired width of the spray pattern, the gun is held six to ten  inches  from  the  work.    If  all  other  adjustments  are correct,   greater   distance   will   result   in   dry   spray   or dusting  and  excessive  overspray.    Holding  the  gun  too close  to  the  work  will  result  in  coatings  which  are  too heavy and will have a tendency to sag or run. (3) Stroke    technique.        The    technique    of proper  stroking  requires  maintaining  the  same  distance between  the  gun  and  the  work,  the  same  speed,  and keeping the gun as near to a right angle to the surface as possible throughout the entire pass. (a) Distance.  The natural tendency for spray     painters,     particularly     when     tired     or     in     an uncomfortable  position,  is  to  arc  or  wave  the  gun,  as shown in figure 5-5.  This practice must be avoided at all costs, because it causes a thicker coating to be applied in the middle of a stroke than at the end. (b) Speed.    Maintain  a  constant  speed through  the  pass.    If  the  motion  is  slowed  at  any  point and   the   paint   output   is   not   changed,   an   excessive amount of paint will be deposited, causing it to run or to sag. 5-1