Ejector pump check valve making 3 knocks when closing

[Qwertyjjj]

Check valve was replaced when I replaced the entire ejector pit.
It seems to occasionally be making a triple thud instead of just the normal one thud when closing.
Any ideas what could cause this?
Doesn't seem to make much difference in operation but just seems a bit odd.

 

[FullySprinklered]

Sounds like you got the dreaded Tony Orlando check valve. Just Dawned on me.

 

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[xprtplumber]

Ejector pumps will most always bang pretty hard when the pump disengages, this is due to the heavy water column in the 2" discharge slamming down on the check valve flap. Where I work we always install soft close spring loaded check valves when installing or replacing sewage ejector pumps it costs a bit more but there is no banging noise and the customers a much happier with the product and installation.