In some embodiments, a capacitor includes a first conductive layer electrically coupled to a first terminal, a second conductive layer electrically coupled to a second terminal, a floated conductive layer disposed between the first and second conductive layers, and a plurality of non-conductive layers respectively disposed between each of the conductive layers. The base unit has a first through hole having a first tapered portion. The first member is disposed at least partially in the central bore of the valve body and includes a shaft portion and a sealing portion. Fresh air enters from the air intake valve and is then downwardly introduced into the box body through the drainage channel and pushes air originally within the box body to exhaust it away from the air vent valve to allow air within the box body to perform circulation.