This plug is designed to provide an effective secondary seal on the valve. This is a requirement for some life raft approvals. This plug can also be useful in preventing air loss through the pressure relief valve when an inflatable chamber is experiencing heavy impacts in rough seas which can cause pressure spikes.
The plug is highly resistant to ozone, oil and other contaminants normally found in the marine environment.
Please note that with the plug in place the valve is no longer able to function as a pressure relief valve.