Abstract: A closure-port type valve is constructed so as to minimize internal stresses and lengthen valve life. A limit plate is secured between a valve bonnet and a valve body; the limit plate halts motion of a diaphragm compressor as the compressor moves the diaphragm toward a valve-closed position. The limit plate and compressor are provided with surfaces which substantially completely support the diaphragm when the valve is fully opened. The limit plate and valve body seal and retain an outer diaphragm edge while achieving metal-to-metal contact, thereby preventing leakage and rocking movement which might otherwise be caused by repeated valve operation, or externally applied forces, such as overhung loads from actuators or seismic shocks.