The HAV-501 air adjustment valve attaches to the spray gun inlet, allowing the operator to control pressure at the gun. The HAV-501 includes an air guage. The swivel top allows fast, easy installation. For use with all professional spray guns. The HAV-500 is the same valve as the HAV-501 without the gauge. P-H-5516 air adjustment valve attaches directly to the spray gun air inlet. Commonly used with spray guns, pressure tanks and pumps, the valve features a large knurled knob for adjusting the airflow.