high pressure pumps
Chemical pump,Dosing Pump,High pressure pump,Dosing Equipment > news > Views
balancing system with balance disc. Its bearings are medium lubricated, so – in contrast to Type a – it requires no oiling or greasing. As the title indicates, the intention here is to draw a hydraulic comparison of the two types of pump. Considering the central importance of energy expenditures in large RO plants, and due to the fact that those costs are primarily dictated by the power requirement of the high pressure pump, this comparison focuses first and foremost on the pumps’ theoretically achievable efficiencies.
Achievable efficiencies
The Institute fur Turbomaschinen und Fluidantriebstechnik (TFA) at Darmstadt Technical University in Germany developed within the framework of a long-term research project a package of programs called ‘ETAMAX’. When a certain set of boundary conditions is inserted, the program enables close estimation of the maximum theoretically achievable efficiency of a given centrifugal pump. All individual losses occurring in a centrifugal pump (with the exception of mechanical losses in bearings and shaft seals) are modelled and grouped together as the so-called ‘internal efficiency’, η i. With the aid of a postulated mechanical efficiency, ηmech, assertions can be made concerning the pump’s overall efficiency, η pump: ηpump = η i•ηmech Modelling of the internal losses is limited in principle to defining the duty point that offers the best efficiency (‘ηmax’). Once the pumping data and the free variables are given for that load point, the program calculates an ‘optimal’ geometry of impellers and diffuser elements. No consideration whatsoever is given to the fulfillment of such special requirements as good cavitation and vibration behavior. However, realistic limits are set for several geometric variables, for example, the gap width. This precludes the postulation of geometric properties that could prove infeasible when it comes to actually building or operating the pump. This program has already been used to define and publish theoretical upper limits for maximum achievable efficiencies for various types of pumps handling cold water2,3. Accordingly, the maximum achievable efficiency is a function of:
The pump’s type of construction,
Its specific speed, nq =n•(Qn)0.5/(Hn)0.75, and
The absolute quantity of its nominal capacity, Qn,
Where n is the speed in rpm, Qn the capacity in m3/s, and Hn the stage head