NorTrac Cast Iron Two-Stage Pump -&nbsp;16 GPM, 1/2in. Dia. Shaft, Model# CBN2-13/3.0S Both large and small displacement pumps work together to provide faster extension at low pressures Small pump works individually at higher pressures to greatly reduce power consumption 1/2in. dia. hardened steel shaft delivers 3,600 rotations per minute Check valve and unload valve for top performance Continuous usage