Port Valves Port valves are in fact one-way valves but instead of allowing forward flow they allow instruments such as catheters to open and pass through the valve and close automatically as soon as the instrument is withdrawn. This way they act as a port. Application examples are catheter introducer valves and Trocar valves for Laparoscopic surgery. The valve components that are available for this kind of function are: Duckbill valves Dome valves