If the swing type check valve is installed on the riser, the fluid flow must be from bottom to top. I found a typical installation error: Seen from the shape of the gland (flat), the check valve is a lift type (lifting valve body like shut-off valve), but it is installed on the riser, which is wrong! The swing-type check valve should be installed on the vertical pipe, and the fluid is from bottom to top. Once the emergency stop, the valve flap automatically resets due to the dual action of the valve's own gravity and fluid return, which plays a role of non-return; If the swing check valve is installed on a horizontal pipe and has been running for a long time, due to the rust of the valve shaft, once the emergency stop, there will be serious consequences. When the valve flap is suspended in the air and cannot be reset, it will not function as a check valve. Therefore, the swing check valve is installed on the horizontal pipe and must be checked regularly! Lift check valves can only be installed on horizontal pipes.