I am replacing a PRIMARY sump pump with a combo primary/baCKUP UNIT.
The old unit has a check valve behind a wall.....
the new unit has a check valve on the pump.
questions.... can I leave the old check valve behind the wall as it is?
Will there be any issues with having two check valves on the same discharge pipe?
could there be a vacuum created between the 2 check valves that would prohibit the new pump from discharging?
any advice is much appreciated.