The QS4P pumps are manufactured by ZDS. They are pumps with floating rotor with axial play, which allow water circulation with greater amount of sand, for the movement of the rotor allows the water to move the sand preventing clogging.
The QS4X pumps are manufactured by ZDS and they are pumps with floating rotor with axial play, have stainless steel cast heads to withstand higher pressures and flow rates.