A pilot-operated valve employs an external self-actuated auxiliary pressure-relief valve which is referred to as pilot, alongside the main valve in order to operate more precisely compared to spring-loaded valve. The pilot-operated valve includes pop-action and modulating types.

These valves are flanged type and are based on API 526 standard. These sizes vary from 1”x2” up to 8”x10” with flange ratings of #150×150 up to #2500×300.