Dig a hole over the irrigation line at the point where the sprinkler head is to be added. When digging out the sprinkler head in a turf area, cut out a section of the lawn and set aside for replanting later.
Mark the location on the PVC pipe where the saddle-T fitting will be installed. Slide the saddle-T onto 1/2" polyethylene tubing (Image 1) and tighten down securely with a nut driver (Image 2).
With the core tool, push down in the center of the saddle-T fitting and twist. A small hole will be cut from the pipe. Place a barbed fitting into the hole of the saddle-T and screw down tightly. Push an 18" section of 1/2" polyethylene tubing onto the barbed fitting securely. Screw another barbed fitting into the base of the sprinkler head (Image 1). Heat the open end of the tubing with a propane torch. Be careful not to burn the pipe; a few seconds with the torch is sufficient to heat up the pipe and cause it to expand slightly. Then push the tubing onto the barbed fitting as far as it will go.
Set the 4" sprinkler head in place (Image 2) and backfill with dirt. A good way to keep the sprinkler head in place while you do this is to place one hand down onto the sprinkler head and push down so that it is flush with the ground. With the other hand, push several handfuls of dirt into the hole and pack it tightly around the sprinkler head. Continue backfilling until the sprinkler head is level and flush with the ground. Be sure to leave the protective cap on the sprinkler head in place during the installation.
Turn on the zone without the nozzle on the new head; this flushes soil or other debris out of the waterline that may have gotten in during installation. Then turn off the zone. Screw the nozzle tightly onto the head, remove the protective cap and adjust the spray range.
Replant the sod around the new sprinkler head and water as needed until the grass is re-established.