Description The A-520 static pressure probe is designed to sense static pressure in a duct, plenum, air handler, or other type of HVAC equipment. The probe has two vertically opposed orifices that cancel out any airflow-induced errors. If a bent tube with a single orifice at the end is used to pick up static pressure in a duct, the air flowing across the probe may cause a small low pressure within the probe. This low pressure acts against the duct static pressure and hence induces an error that is exponentially proportional to the airflow. As the airflow increases, this error will increase also, and as the flow decreases, the error decreases in an exponential relationship. The engineers at MAMAC Systems resolved this problem with a unique design that incorporates two orifices diametrically opposing each other in a vertical plane. When the air flows across an orifice, it creates a suction towards that orifice. Similarly, when the same air flows across the other orifice, it creates an opposing suction that cancels out the first pressure drop. Regardless of the velocity, the flow error is constantly canceled out and the A-520 provides an accurate, repeatable, and stable static pressure value. The A-520 is available in 6061T-6 aluminum alloy for standard HVAC applications and can be ordered in two probe lengths: a four-inch probe and an eight-inch probe. The probe is attached to a two-inch O.D. flange with two conveniently located mounting holes for easy installation against sheet metal. The flange also has a neoprene gasket to seal off the mounting holes. Furthermore, an industry standard ¼" hose barb or 1/8" NPT female swivel brass fitting is provided for PVC/copper tubing connection.