In article ,
Ned Simmons wrote:

I don't know if every submersible well pump has a check at the pump,
but it seems to me a deep well pump (more than 30 ft, or 1 atmosphere
of water column) should. I do know mine does, and if you look at the
documents on Goulds' site all their deep well submersibles also do.

The check valve at the submersible is required since below 33 ft the
water column would separate and you would get a big BANG when you
started the pump and the columns collided.

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