Abstract: A relief valve to be used in cases for transformers submerged in oil that requires periodic testing for concentration of pollutants. A T-shape body having an upper tubular member with an internal through passage with an internal thread inside one of its ends and the other end having an external thread that is cooperatively received within a threaded bore in a transformer case. A perpendicularly extending tubular member includes an exhaust chamber wherein a spring loaded valve assembly is housed. The load in the spring is predetermined to permit the pressure that builds inside the case not to exceed a predetermined value. Using a flexible plastic tube that is insertable through the internal passage and applying a pressurized gas, preferably nitrogen, through the tire valve, a specimen of the liquid inside the case is extracted for analysis and testing without having to open the case.