Pitot tube pumps excel in low flow high head applications and are able to operate reliably throughout their full curve (shutoff to runout) without damage. This makes them a great choice for tough applications in which there is high fluctuation in flow rate.
The most common pitot tube pump commercially available is an overhung rotor arrangement with an coaxial suction and discharge. 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 eliminate axial thrust resulting from suction pressure. It has been demonstrated that size and number of blades of the pitot tube has a large impact on the pressure distribution inside the rotating case. There is region of higher than anticipated pressure at the center of the rotor. This pressure adds significantly to axial thrust loads and increases seal pressure (in the between bearings arrangement). This has a large impact on bearing life and seal selection. Adding enclosed channels to the rotating case eliminates this pressure without sacrificing pump performance reducing the size and number of bearings required and increasing bearing life.
