The Design and Theoretical and Experimental Study of the Plastic Hydraulic Valves
Authors: Marciniak Lubomir , Banaś Michał , Stryczek Jarosław 
Published: November 2016

The overall popularity of plastics has not reached the industrial hydraulics yet. They are already widely used as a material for seals and minor parts, such as handles, covers, caps, etc., but still the dominant material for the making of the key elements is steel.
The main project carried out by the Fluid Power Research Group of Wroclaw University of Technology is a fluid power system with the major elements made of plastics. The primary goal is to make a set of prototype plastic elements that within a low pressure range will perform comparably well to the elements which are traditionally made of steel and are available on the market. That set includes two basic hydraulic valves: the pressure relief valve and the on/off valve. The authors present the research that has been done on them so far, as well as evaluate the possible advantages and problems associated with the application of plastics for the making of the system.1
The analysis of the traditional, metal valves’ designs was done as the theoretical base for the plastic valves’ design. All the main parts were studied, especially the main operating elements (poppet and its seat or a piston). In the paper, the references have been provided where possible. All the analyzed features are discussed in terms of using plastics as the main material. In the summary, it is pointed out which of them could easily be transferred, which need to be tested and which are clearly non-transferable and need to be redesigned.
Based on guidelines resulting from the analysis of the traditional metal valves, the first plastic prototypes of the pressure relief valve and the on/off valve were designed, constructed and tested by the FPRG. Details of the design are discussed, focusing on its versatility achieved by the usage of interchangeable parts. The early design problems are also shown, as well as the way how they were dealt with. The steady state characteristics are presented and compared to industrial metal valves of the similar size available on the market.
A part of the improvement process was an analysis of the flow inside the valve conducted by means of Computational Fluid Dynamics (CFD). The results and conclusions of the flow analysis are presented.
The main differences between the plastics and steel are the mechanical properties, especially the lower rigidity. Much larger deformations of the loaded elements can possibly cause problems. Using the CFD results as loads, a structural analysis by means of the Finite Element Method was also carried out. The results and the discussion on whether the deformations are substantial or not and what kind of problems they may cause are presented in the paper.
In the summary, the authors draw conclusions from the conducted design process and tests on the first generation prototypes, as well as discuss the reachability of the research objectives defined at its beginning, which regarded the plastic valves. The design of the second generation prototypes is also briefly discussed and the future research plans outlined.