Below is a list of Pressure Vessels manufacturers from Appleton, Wisconsin. Pressure vessels, often referred to as air pressure tanks are used for the storage and containment of fluids, vapors or gases at pressure levels greater than that of atmospheric pressure. They are designed to operate at pressures more than 15 psi, and are made of a variety of metals, high-strength plastic or fiberglass. The tanks are usually cylindrical in shape with a horizontal or vertical orientation.