Yes. The green vent cap on your aeration compartment cover must be free and clear of obstructions to allow fresh air to enter the Jet system. Jet systems are designed to inject fresh oxygen into the center treatment compartment to ensure the best performance from the aerobic bacteria living in the plant. Aerobic bacteria are just like any other living organism and more fresh oxygen means more bacteria. Depriving these bacteria of fresh oxygen by covering or burying the vent cap will inhibit the growth of these bacteria and may make it difficult for your system to recover from any toxic or overloaded conditions that it may experience.