The GSZ-4-series is a submersible three-phase, cast iron, high head, high volume, heavy-duty drainage pump driven by a 4-pole motor. The side discharge, spiral design allows smoother passage of solids which reduces abrasive wear. The motor is cooled by a water jacket that gives efficient motor cooling even when the pump operates with the motor exposed to air. The pump incorporates seal pressure relief ports that relieve the pump before it reaches the shaft seal.