Description The OPW 623V-2203 is a 4IN X 4IN Fill Adaptor Bronze Top Seal. It threads onto the 4 inch fill pipe of underground storage tanks to mate with top-seal delivery 4 inch elbows. Pressure Vacuum Vents are installed on the top of vent pipes from underground or aboveground fuel storage tanks. The vent cap and internal wire screen are designed to protect the tank vent lines against intrusion and blockage from water, debris or insects. A normally closed poppet in the valve opens at a predetermined pressure or vacuum setting to allow the tank to vent.