What would cause the 81 AF-8, nonsurge check valve (CV) to fail to open?

The primary reason the 81 AF-8 nonsurge check valve might fail to open is due to the closed downstream manual valve. When this valve is closed, it creates back pressure in the system and prevents water from flowing through the check valve. Check valves are designed to permit flow in one direction and rely on the pressure differential across them to function correctly. If the downstream path is blocked (as occurs when the manual valve is closed), then there is insufficient pressure to push the valve open, resulting in malfunction.

Options regarding valve installation or component integrity, such as the orientation of the Hytrol check, the condition of the diaphragm washer, or the presence of air in the main valve cover chamber, refer to different aspects of valve function. While these factors can cause issues in other contexts or types of valve operation, they do not specifically cause a check valve to fail to open due to the lack of flow generated by a closed manual valve.