A pressure relief valve prevents a dangerous build - up of pressure when the hydraulic cylinder's piston reaches the end of its stroke. (en.wikipedia.org)
A spring - loaded pressure - relief valve pops up as pressure builds, rising to indicate one red line for low pressure and two for high. (bonappetit.com)
I became a full time fire fighter and continued to develop my own work as a stress relief valve. (artweb.com)