The diaphragm style check valve has a flapper that is secured at the center. The top and bottom thirds of the rubber seal are
“hinged” so they flap open when water flows through the valve in the proper direction. The rubber seal on the flapper provides a positive seal.
When water goes forward through the valve, the top and bottom third of the diaphragm open up and this allows the water through the
valve.
When water attempts to go backwards through the valve the diaphragm closes and prevents the water from going through the valve.