Screw pumps are low-noise and theoretical pulsation-free positive displacement pumps. They are used in oil and chemical industry, as fuel supply and injection pumps in marine and gas turbine applications, as lubrication pumps and as well as hydrostatic drive for presses and elevators.

Screw pumps show a pressure operation limit resulting from lateral hydrostatic loads on the sidewise idle screws. The hydrostatic forces are balanced by hydrodynamic journal bearing forces in the chamber sealing gaps between spindles and casing.

At the chair of Fluid Systems Technologies at Technische Universität Darmstadt a hydrostatic load balance of the idle screws inside the delivering area of the screws has been developed and two prototypes have been build and tested. The system uses the potential of suction and discharge pressure of the pump, and sets compensation pressure on the exterior diameter of the idle screws. Due to the fact that the chamber sealing changes position in axial direction the compensation pressures are switched by the turn angle of the screw itself. Hence the compensation system is passive. Measurements showed a very small additional inner leakage.

The system vanishes hydrostatic loads and enables to drive screw pumps within higher differential pressures.

In hydraulic pumps and motors, the tribological contacts are responsible for the greatest share of hydromechanic and volumetric losses. The most important tribological interfaces in an axial piston machine are the contacts piston / cylinder, cylinder block / valve plate and slipper / swash plate. Other tribological interfaces have minor importance in ordinary operating points.

In the past, a couple of simulation approaches have been presented for simulating the tribological contacts of axial piston machines. These approaches have different conditions and goals considering different physical effects. In all simulation approaches, the Reynolds equation which describes the characteristics of the fluid film is taken into account. Moreover deformations as well as the micro-movement of the involved parts, thermic effects, cavitation, solid contact and mixed friction can be considered. The friction torque between cylinder block and valve plate consists of viscous and solid friction. For high operating speed viscous friction is dominant, while for lower speed mixed friction becomes more relevant.

In this paper, a simulation model for the tribological contact cylinder block / valve plate is presented. Micro movement of the cylinder block and models for solid contact and mixed friction are implemented, so that it is possible to run realistic simulations for high and low speeds. Moreover, geometric variations of parts in an axial piston machine are simulated. The simulative results are compared and discussed with regard to friction and leakage losses.

Noise emission of hydraulic drives represents a major subject in many applications. As hydraulic pumps are the primary source of oscillations leading to noise, present major issues in pump development are minimizing the flow ripple and the resulting pressure pulsation as well as reducing direct oscillations of the mechanical structure. For this reason, pump simulations have become more and more important. The variety of model types ranges from simple and universal approaches concentrating mostly on the flow ripple up to construction specific models with respect to both, structure and fluid mechanical effects.
Whereas complex, construction specific simulation models work with tree-dimensional design aspects of the pump, more simple and universal models try to describe certain functional characteristics by defining less complex, two-dimensional parameters, such as the volume of one displacement chamber relative to the driveshaft angle or the variations of areas for flow transfer between chamber and ports. This type of model is rather common in today’s industrial development.
Insofar as the shapes of displacement chamber and corresponding elements can be described by simple mathematical functions, simulation parameters can be derived easily from the dimensions of the related design elements. A good example of such pump geometry is an axial piston machine with circle-shaped endings of ports and chamber opening as well as symmetric pre- and decompression grooves. If the shapes of displacement chamber and ports are more complex and difficult to describe by means of mathematical functions, the simulation parameters cannot be linked directly with dimensions of design elements. Typical examples of these geometries are gear pumps. In this case, parameters have to be calculated by approximation. Finding an appropriate software solution for this is important, because with every change in the functional design of the pump one or more simulation parameters have to be recalculated.

In this paper, a fast and universal method for deriving two-dimensional simulation parameters from complex pump geometries will be presented. The method provides two types of information. First, a modular structure that allows to easily build up a parameterization tool for any pump geometry. This can be seen already on a very high level, where every single parameterization procedure consists of modules for assembly, motion and calculation of the demanded output. Secondly, the method offers a set of algorithms for the calculation of closed and partial functional areas, as well as algorithms for position calculation of pump elements that have to be positioned in an iterative way on the basis of certain conditions of contact. A typical example for this need is the relative angular positioning of gears or vanes. By defining the cutting points between the calculation modules just on the basic principle of hydrostatic pumps, the method is applicable to different types of pumps, taking gear and vane machines as examples. Even combined functional principals are covered.
The presentation will start with a short introduction to the general approach of modeling pumps by defining two-dimensional parameters. After that, the overall concept of the method will be explained by showing, how the modular structure of parameterization can be adapted to different types of pumps. This will be followed by a closer look at some of the algorithms used in this method. By taking one complex pump geometry as an example, specific calculation results for common parameters will be discussed, such as the variations of displacement chamber volume and flow transfer areas. At this point, the main focus will be laid on accuracy and calculation which usually represent the most interesting aspects within the industrial development process. At the end of the presentation, the potential of the method for deriving additional, new parameters will be estimated.

Oil pumps, including vane, gerotor, crescent and external gear pumps, are a critical component in many industrial applications. Generated rotor (gerotor) pumps are internal rotary positive-displacement pumps in which the outer rotor has one tooth more than the inner rotor. The inner and outer gear tooth profiles are described by epitrochoidal equidistance and circular arcs respectively.
Due to their compact design, low cost, and robustness gerotor pumps are commonly used for cooling, lubrication, and filtration systems, for pumping liquids such as oil, transmission fluid, and fuel. They provide high volumetric efficiency and smooth pumping action and they work well with a wide range of fluid viscosities.
In this paper a new gerotor pump with innovative gerotor design is presented and fundamentally investigated by means of full three dimensional transient Computational Fluid Dynamics (CFD) analysis. Five gerotor pump CAD models (having from 8 to 12 teeth of the internal gear and from 9 to 13 teeth of the external gear) were designed and compared to a standard gerotor pump (having 8 inner rotor and 9 outer rotor teeth). The results from the simulation showed a substantial reduction of the flow and pressure ripple of all five models. Furthermore the flow rate and the volumetric efficiency of all gerotor pump models were predicted. Finally a prototype of the first CAD model was built and its simulation results were compared to the experimental data with excellent agreement.