## 2 Materials and Methods
### Experimental  
The use of additive manufacturing methods in the design process can quickly produce working prototypes. These prototypes can be used as an effective validation tool, both functionally and aesthetically. This helps in finding flaws at the testing stage and ensures a better product. In this study, fused deposition modelling (FDM) technology was used to develop a prototype of the valve. A Ultimaker 3D printer was used to manufacture the prototype. Acrylonitrile butadiene styrene  
Figure 5: Fluid flow through extracted fluid profile of valve. (ABS) material was used for 3D printing as it provided better strength when compared to the other available materials in the printer. For the support structures, Polyvinyl alcohol (PVA) was used. To facilitate the manufacturing and assembly of the valve, the prototype was manufactured in three steps. In the first step, the valve body was manufactured. For ease of assembly of the body onto the testing rig, a base plate was added. The second step included the bonnet fabrication. The bellow in the bonnet was replaced with a cylinder through which a push rod could move. This is because the material used (ABS) does not provide enough elasticity to produce a functional bellow compared to metals. The third step of manufacturing was to make all of the internal components including the links, disc, and push rod. All components were printed as separate parts to be assembled together. Keeping in mind that the prototype will be used for experimental analysis, design changes were made to allow for the convenient mounting of sensors on the valve to collect experimental data. The bonnet design was edited to place the force sensor between the handle and push rod. Connectors were added at the end of the valve to mount pressure gauges. After finalizing the design to be manufactured, the design was imported to Ultimaker Cura for pre-processing using an Standard Tessellation Language (STL) file format. Ultimaker Cura is a dedicated software for Ultimaker 3D printers that provide pre-processing options such as customized initial parameters, support structures, and build orientation. Parameters used for 3D printing are tabulated in Table 1.  
The prototype was printed in three steps: the valve body, bonnet, and components. One hundred percent infill density with resolution of 0.1 mm was used to print all parts to obtain the maximum strength. The total time taken to print all parts was 48 h. After the successful manufacturing of all parts, some post processing operations were performed. Post processing only included the removal of support structures by immersing the part in warm water. As built surface finishing was used. No finishing treatments were applied after manufacturing. The 3D printed parts provided good dimensional accuracy for testing. To remove the support structures, all parts were immersed in water, as the support structure material is water soluble. Filing was done, where required, to remove the extra material for assembly. All printed parts were assembled together to obtain the final prototype. The manufactured valve components and assembled valve is shown in Figure 6.  
For this study, the bellow was assumed and produced as a solid cylinder as FDM cannot provide enough elasticity for the bellow function. Force on the valve disc was assumed to be equal to the fluid pressure acting on the disc. Additionally, the dimensional accuracy of the printed parts was assumed to be similar to the modelled part with a difference of 0.2 mm. However, these assumptions do not affect the accuracy of the simulation and experiment as the bellow profile does not affect the flow profile of the fluid through the valve; there will be less force acting in real life due to pressure losses and geometric tolerance does not have a significant effect on flow. After fabricating the prototype, the prototype was subjected to experimental testing for position, force, and flow analysis. Sensor and gauges were mounted on already manufactured mountings during the manufacturing process.