The most common pitot tube pump commercially available is an overhung rotor arrangement with a coaxial suction and discharge. This White Paper from Weir discusses how this arrangement has a large impact on the Net Positive Suction Head required (NPSHr) by the pump. Often the NPSHr must be increased substantially when pumping fluids with steep vapor pressure curves such as light hydrocarbons. In this arrangement, axial thrust is dependent on suction pressure. High suction pressures result in high axial thrust, requiring multiple thrust bearings and reducing bearing life. A between bearings rotor arrangement with opposed suction and discharge has demonstrated improved NPSHr and eliminated axial thrust resulting from suction pressure.
The White Paper can be accessed by clicking here