A check valve includes an upper housing defining an inlet of the check valve, and a lower housing having a seating portion and defining an outlet of the check valve. The check valve further includes a chamber interposed between and defined by the upper and lower housings for fluidly connecting the inlet and the outlet, and a flexible diaphragm mounted in the chamber. The flexible diaphragm selectively permits fluid flow in a first direction, and prevents fluid backflow in a second direction opposite to the first direction. The flexible diaphragm includes a color changing material, and when the flexible diaphragm is seated on the seating portion and bent due to force of the fluid flowing in the first direction, the flexible diaphragm exhibits a color change.