I realized that my pool builder installed the SWG cell in the vertical pipe after the heat pump without a check valve between it and the heat pump. The installation manual for the Jandy heat pump shows a check valve in the vertical and the SWG cell installed after the loop before the pipe heads into the ground to return to the pool. Since my pool is inground and is below the level of the pool equipment, is there any need for a check valve? I do not have any in the system now and it works fine. I am more concerned about residual chlorine in the SWG cell draining back into the heat pump and corroding the heat exchanger. I am considering making a vertical loop and relocating the SWG cell to the side of the loop that goes into the ground. If I do this, is there any need to install a check valve before the SWG cell? Once the pump shuts off, whatever water that is left in the cell will drain back to the pool by gravity. I would rather not add the additional resistance of a check valve into the hydraulics if it is not required.