1/4" Hose Barb Check Valve, 3 psi Cracking Pressure 302 Stainless Steel Spring, 316 Stainless Steel Ball, Viton Seals, Natural Polypropylene.Safety is paramount when working with glass vessels that see pressure.Hydrophobic vent filters can become blocked due to moisture form the vessel contents. This results in a higher-than-normal back pressure and an increased chance for the vessel or other system components to fail.The pressure relief valve should be used in situations where the glass vessel could see pressure.The valve is a one-way or non-return device to let gas flow in one direction above a fixed pressure level.It is attached by silicone or comparable tubing to one of the vessels head plate ports. If the pressure inside the vessel reaches 3 PSIG, the valve will open and then close when the pressure falls below 3 PSIG.The housing cannot be opened nor can the pressure setting be adjusted.