The PLASTIC MUSHROOM STYLE TANK VENT CAP, or tank breather cap, keeps out debris, insects, seeds, and rain while allowing tanks to properly vent. All plastic construction is corrosion proof.
How much air flowthe vent caps are capable of, is a common question. The answer is that there is no real limit to the amount of flow through the vent caps, but as the flow increases, the back-pressure created increases. (same as with a valve or elbow in the pipe) So the real question becomes: how much back pressure will your system tolerate at the maximum anticipated air flow rate? The relationships are described in the chart.