PuK - Process Technology & Components 2022

Components Novel valve technology Novel valve technology for oscillating displacement pumps Prof. Dr.-Ing. Eberhard Schlücker, Daniel M. Nägel, Dr. Peter Kugel, Philipp Werhan, Michael Feist Solid-liquid mixtures always pose challenges for oscillating displacement pumps – performance depends on the only wear part, the check valves, and their condition. The high dynamics of the opening and closing processes and the excessive stress on the materials lead to wear and tear. Additionally, the constructions are prone to malfunctions, which cannot be avoided with conventional designs. The patented valve design presented in this article was developed by FELUWA Pumpen GmbH together with iPAT Erlangen. The objective was to avoid known weak points/phenomena and to increase the service life of the pumps. Classic valve technology and their weak points Ball, cone and plate valves are most commonly used in process technology, with ring plate valves also being used occasionally (Fig. 1). All valve types can be optionally equipped with or without a spring. The ball valve without spring is a popular valve for abrasive suspensions, due to the even wear, as the ball keeps turning slightly due to the asymmetric inflow. In fact, the ball valve may still operate reliably even when the ball has lost 10 % or more of its diameter. For precise dosing applications, double ball valves (Fig. 2) are used. As the size of the valves increases, the sealing body is more likely to be spring loaded to reduce the closing delay of the valve, but this results in the loss of ball rotation, making the function similar to that of a cone valve. On the other hand, balls up to 300 mm in diameter are used for slurry pumps, though these are hollow balls in order to keep the closing energy reasonably small here. Fig. 2: Double ball valve for increased dosing accuracy Close-fitting guide ribs ensure that the ball closes precisely, but at the risk of larger particles in the slurry blocking the ball and ball guide. The stroke frequencies achievable with ball valves are applicable in the range up to approx. 180 min -1 and at medium viscosities. The plate valve is only designed without a spring in exceptional cases (small or very inexpensive pumps). The spring usually serves as a plate guide and thus allows for a guide-free and simple valve casing. The sealing body mass of a valve plate and with it the closing energy are relatively small, which allows for high stroke frequencies. The freedom in the movement of the plate caused by the spring guide often results in an uneven or non-rotationally symmetrical touchdown. This leads to valve chattering and the consequent wear, and suddenly a small step has to be bridged, thus allowing leakage currents. This problem is avoided by using clear and raised contact surfaces and resistant or hard materials. The danger of uneven closing remains, however. The larger the valves, the greater the effect of the disadvantages described, which is why cone valves are usually used for larger configurations. They are always spring- loaded and require guides. This alone results in the biggest problem of their con- Fig. 1: Valve types Ball valve Cone valve Plate valve 100 PROCESS TECHNOLOGY & COMPONENTS 2022

Components Novel valve technology struction: the guide needs to be narrow enough in order to function as such. The guide diameter is significantly smaller than the diameter of the cone plate. If a particle now gets under the cone, a large bending moment acts on the transition between the guide pin and the plate (step), which can lead to rupture. The same occurs when the guide is of low quality: the sealing body touches down asymmetrically and centrally slips into the end position. For this reason, reinforcement rings made of elastic materials are used in cone valves. These are chambered by the installation groove and mating surface inside the cone and can buffer the described attacks. At the same time, this design makes for optimum use of elastomers, which also provide a certain degree of wear resistance when used with slurry. Fig. 3: Cone valve with additional reinforcement ring as a buffer for the ensuing positioning errors. The above illustrates that a ball valve without a spring would actually be the ideal construction for slurry, were it not for the large mass of the ball (closing energy and stroke frequency limitation). On the other hand, plate valves would be ideal if not for the problems described. Furthermore, for designs with guides, there would have to be a way to buffer the trapping of particles. Cone valves have therefore proven to be the best choice for critical applications with high flow rates. The ideal valve In negative terms, the fluid valves commonly used today are a necessary evil. That is, unless a design is possible that allows for precise closing, combined with perfect guidance Fig. 4: Novel valve with spoked diaphragms where required. When equipped with two spoked diaphragm guide elements, this kind of valve is possible. Fig. 4 shows the ideal valve with two spoked diaphragms (orange shown), one above and one below the sealing body. The spokes are connected with inner elastomer rings for clamping positioning in the valve guide and outer rings that can serve as sealing elements for the valve casing. The spokes replace the spring and at the same time ensure perfect guidance. Fig. 5: Novel spoked valve after 900 h of operation in iron oxide slurry Initial operating experience with iron oxide slurry (Miller number 140) led to astonishing results. After 900 hours of operation, there were little to no visible signs of wear on either the spoked diaphragms or the sealing area. High-speed camera recordings confirm that this can be attributed to the flawless guidance through the spoked diaphragms. This makes this new type of spoked valve superior to the previously listed valve types, as the described functional faults will no longer occur. Summary The presented valve with novel spoked diaphragm technology (European patent no. 3497333) represents an important advance for valve technology in oscillating displacement pumps as well as other applications, and is an optimal solution for pumping abrasive solid-liquid mixtures. In contrast to steel components, the spoked diaphragms made of elastomer do not show any noticeable wear, thus have a longer service life and are suitable for critical applications. The first long-term tests prove that the novel design will increase the availability of positive displacement pumps and reduce operating costs. The Authors: Prof. Dr.-Ing. Eberhard Schlücker, Friedrich-Alexander University Erlangen-Nuremberg, Institute of Process Machinery and Systems, Engineering (IPAT), Erlangen Daniel Nägel, Managing Director Technology, FELUWA Pumpen GmbH Dr. Peter Kugel, Product Design, FELUWA Pumpen GmbH Philipp Werhan, Product Design, FELUWA Pumpen GmbH Michael Feist, PhD student iPAT Erlangen, Germany PROCESS TECHNOLOGY & COMPONENTS 2022 101