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Pumps and Systems
Pumps and Systems Diaphragm metering pumps The challenge of the shared oil bath In practice, the development work was accompanied by an FMEA (Failure Mode and Effects Analysis) and risk assessments according to MRL and ATEX. The design was carried out with the aid of an advanced 3D CAD system and was validated by the use of kinematic collision analyses. “In addition, we perform strength calculations in product development according to the classic finite element method (FEM) as well as computational strength verifications according to the FKM guideline (computational strength verification of machine components),” explains an RD Engineer, Research & Development Mechanics from the supplier. “FEM is known to be used to determine deformations of components under certain load boundary conditions, such as assembly forces, transport forces and accelerations, and operating forces and accelerations.” The strength verification according to the FKM guideline is then used to determine the load factor of the component under static and dynamic boundary conditions – and thus the operational strength. This enabled the German manufacturer to reduce the amount of testing on real components and thus shorten the development time for the LCC and LCD models. “These calculations are also particularly important for us because our units are often used to convey hazardous fluids,” adds another Engineer. “In the simulation, worstcase scenarios are considered that are sometimes very difficult to implement in tests. This way, the risk of accidents can be significantly minimized.” In accordance with the design concept, focus was not only on the safety and robustness of the units but also on reducing the number of parts. In the course of the project, for example, it was checked whether a shared oil bath and the direct connection of the plunger to the connecting rod, which could potentially eliminate five components, could be implemented in practice. “The compromise of using only one kind of oil for lubrication and the transfer of hydraulic energy is something we have verified in many thousands of hours of endurance testing,” the Engineer says. Many series-produced drive unit components could also be taken over due to their high volume and the resulting suitable costs. However, this also led to challenges. For example, in order use the series-production connecting rods and achieve an easy assembly, the positioning of the worm shaft in the drive element housing was changed which caused a change in the oil dynamics. During operation, the oil was distributed unevenly in the drive units of the triple pump and an oil wave formed. This impeded the oil exchange between the multiplex drive unit, which had an unfavorable effect on lubrication and hydraulics. Solution with the help of a simulation of oil movements with SPH “We were able to see the effect on the physical test object, but it was difficult to look inside the components to determine exactly what was happening there and how it could be fixed,” the Engineer said. Therefore, the engineers needed a simulation method to illustrate the processes within the drive unit. However, the CFD and CFX methods used to simulate pump behavior to date were not very suitable for figuring out the phenomenon, as they would have required an enormous amount of time, and thus money, for this problem. For this reason, the engineers decided to take a new approach and use a method originally developed to deal with astrophysical problems in three-dimensional space for the first time. SPH is a particle-based method and is generally used when highly dynamic and strong flows or free surface flows need to be simulated efficiently. Classic application areas include the simulation of oil flows in vehicle transmissions or the simulation of tank sloshing. “We had to do several cycles, including investigating a few hypo theses on the physical test object, but we ultimately obtained reliable simulation results very quickly that reproduced the observed flow behavi or well and in a usable way,” the RD Engineer explains. “The simulation has helped us tremendously in understanding the phenomenon.” Corrective measures were subsequently designed and implemented. Further simulations and the subsequent validation of the modifications used showed the desired homogeneous oil distribution and low oil movements on the surface. Fig. 6: Examination with SPH method: before – after During operation, the oil was unevenly distributed in the triple pump's drive units, forming an oil wave. To solve the oil wave problem, the engineers used SPH for the first time, a method originally developed to deal with astrophysical problems in three-dimensional space, now generally used when highly dynamic and strong flows or free surface flows need to be simulated efficiently. Pictured: Simulation oil distribution in a triple pump before/after New modular system with 40 % reduction in manufacturing costs The development work was successfully completed in December 2021. The result was a new ecosmart mo dular system consisting of three drive unit performance classes and the associated diaphragm pump heads. The new product range includes single and multiplex pumps, four gear ratios, a manual as well as an electric stroke length adjustment, ten plunger diameters in the hydraulic part and three material variants. Wear-related long-term tests and function-related short tests to determine the technical characteristics and the function under extreme challenging conditions (temperature, pressure, stroke frequencies, input speeds) had previously proven the robustness, durability and reliability of the new low-cost pump range. The BOM structure of the pump product was designed according to the requirements of the automated configuration software (drive element, pump head, drive flange, fluid valves, valve bodies as customer-provided connection adapters). At the same time, in addition to the technical targets, a 40 percent reduction in manufacturing costs was achieved compared to the high-pressure diaphragm pumps of the same size from the ecoflow series. “The experience we gained during this project through the engineering concept, the testing and the measures derived from it have provided us with some new insights and generated knowledge which we will also benefit from in future development projects,” the Team Leader Research & Development Mechanics sums up. The Auhtor: Thomas Bökenbrink, Lead Product Manager Pumps, LEWA GmbH, Leonberg, Germany 44 PROCESS TECHNOLOGY & COMPONENTS 2022
