What is particularly important in the oil sector however – even more important than efficiency – is the flexibility that displacement pumps provide when it comes to the viscosity of the medium. Whilst centrifugal pumps have fixed operating points and their efficiency drops rapidly as viscosity increases, NOTOS® multi screw pumps also operate with excellent rates of efficiency across the entire range of viscosity up to 50,000 cSt, as they operate on the principle of displacement. The pumping principle is based on the interaction between the screws and the housing to form chambers, which continuously convey the medium at stable pressure from the suction to the discharge side, almost entirely independent of consistency or viscosity. The flow rate is determined by the rotational speed, the screw diameter and the thread pitch. It is therefore directly proportional to the speed which can be flexibly adjusted.
And what is more: the pump speed and the viscosity of the medium affect the NPSHr value, which determines the intake behaviour. As NOTOS® pumps can be regulated flexibly, they can keep NPSHr values suitably low to match conditions so that the medium is sucked in without interruptions and tanks can be drained fully, even with viscous crude oil derivatives. At a Brazilian terminal, this is used for transferring polyols: The versatile oil product used to produce plastics and flavourings and as a basis of sugar substitutes has a viscosity of up to 3000 cSt. The oil can still be pumped at normal ambient temperatures of 25 to 28 °C at a rate of 50 m³/h without leaving any appreciable residue in the storage tank thanks to the special technology in the 3NS pumps.
Another advantage of low NPSHr values is that all NOTOS® multi screw pumps can usually be operated beside the tanks. Depending on the design of the pipe work, which may cover several hundred metres, the pumps reliably take in the medium. For highly viscous media or particularly deep tanks that can only be accessed from above, the pumps can also be submerged to guarantee high flow rates even when tank fill levels are low. NOTOS® multi screw pumps allow complete draining of tanks, even with higher viscosity media.