The phrase "pressure valve" refers to a device or mechanism that helps release or control built-up pressure in a system. It prevents any potential damage or danger caused by excessive pressure by safely discharging it. Full definition
As it turned out, the 2018 GT3 was the perfect pressure valve for the market. (automobilemag.com)
Rather than waiting up for some fantastic escape months from now, look for little escapes to act as pressure valves from the everyday stresses of parenting. (babycenter.com)
The only thing I thought of is if there is some kind of pressure valve releasing the system freon (if the auxiliary fan is not rotating and the temperature is too high or in any other extreme case)? (mechanics.stackexchange.com)