Preventing an over pressure condition with a mechanical shutdown valve

A membrane test assembly comprising:

• a pressure source to flow a fluid;
• a membrane test cell fluidly coupled to the pressure source receive the fluid and to hold a membrane;
• a test instrument fluidly coupled to an outlet of the membrane test cell to perform a test on a membrane;
• and
• a mechanical shutdown valve positioned in between the membrane test cell and the test instrument, the mechanical shutdown valve configured to stop a fluid flow to the test instrument when a differential pressure created by the fluid flow through the mechanical shutdown valve is greater than or equal to a differential pressure threshold, the mechanical shutdown valve comprising:
• a diaphragm movable between an open position and a closed position to stop the fluid flow through the mechanical shutdown valve;
• a mesh coupled to the diaphragm, the mesh extending from the diaphragm to an inner surface of the mechanical shutdown valve such that the mesh and the diaphragm limit fluid flow between the diaphragm and the inner surface;
• and
• a set of springs biasing the diaphragm towards the open position, wherein a characteristic of the set of springs determines a differential pressure threshold at which the diaphragm stops the fluid flow though the mechanical shutdown valve.