Operational characteristics of this pressure relief valve are directly affected by back pressure changes. For conventional safety relief valve, only the superimposed back pressure affects the opening characteristic and set pressure value, but the combined back pressure affects the blowdown characteristic and re-seat pressure value. A conventional pressure relief valve is not used when the built-up backpressure is greater than 10% of the set pressure at 10% overpressure. A higher maximum allowable built-up backpressure may be used for overpressure greater than 10%.