Here is a clear and well illustrated tutorial video demonstrating the operational principals of pilot and direct acting pressure relief valves.
There are many available configurations of pressure relief and safety valves, each tailored to accommodate a particular set of application criteria. Understanding how these valves work is important to their proper selection and application to industrial processes and their control.
Safety mindedness is critical for these applications, and you should always talk to an experienced applications expert before specifying or installing these products. Product performance and selection information, as well as application assistance, is available from your local product specialists.
Piping Specialties, Inc.
https://psi-team.com
800-223-1468