I am trying to subject some plastic pieces to temperature and pressure testing while the parts are in a container of salt water. I have a pressure chamber that is pumped to a desired pressure with compressed air. If I put the pieces in the container of salt water in the chamber and then pump it to 20psi, will the pressure felt by the parts be 20psi, or does the salt water affect the pressure the parts feel? Does that change if I seal the container with some air above the salt water? Thanks.