Valves are ubiquitous in almost every industrial application or process. Automotive and heavy equipment manufacturers, mining companies and global energy giants alike could not function without them. Technically a type of fitting (though discussed under a separate category), the aim of a valve is to regulate the flow of a fluid (gas or liquid) by completely/partially blocking or modifying its path. This action is usually performed with the electric, pneumatic, hydraulic or mechanical adjustment of a moving part (stem) that has been submerged into the fluid. Their significance—and the varying conditions they are placed under—makes valve design a considerable task. In this article, we have listed 5 common mistakes that engineers can make in the valve design process.
1. Failing to Use FEM Analysis to Predict Stresses
Versatile and sturdy, valves are used in a wide variety of applications, but often have to deal with stark changes in temperature or significant pressure levels. In such conditions, it’s natural that the components of the valve will experience varying levels of stress. This shortens their life-cycle and can lead to cracks, leaks, and in the worst case, total part failure. FEM (finite element method) simulation can be an invaluable tool for engineers looking to refine and improve their valve design in the early stages, providing constructive information on the location and grade of stress points. While it is also possible to calculate these areas of stress by hand, running a FEM analysis on the SimScale platform takes just a few minutes.
2. Not Taking Advantage of CFD to Improve Fluid Flow
Once you’ve taken into account the static stress on your valve, the next step is to analyze the dynamics at play for the required fluid. The most important factor to consider here is pressure loss due to friction and turbulence. If your valve design produces strong areas of fluid separation or vortices, it can lead to a substantial increase in vibration and noise, potentially requiring the installation of additional pumps or machinery.
Running a steady-state or transient CFD simulation is the fastest and most convenient way to improve your valve design. Look out for high pressure, low-velocity regions to identify separated flows and modify your CAD model accordingly.
3. Don’t Forget the Benefit of Thermal Simulation
Thermal simulation can be an especially useful analysis if your valve is exposed to high or low-temperature fluids. High-temperature liquids or gases, in particular, can cause heightened stress on materials, decrease operating efficiency and damage external components through heat transfer (e.g., melting nearby plastic components).
A form of FEM analysis, in thermal simulation certain thermal loads are prescribed to the object rather than pressure or displacement. With SimScale’s simulation technology, hotspots, problem areas, and heat transfer can be simulated and visualized ahead of any prototype. Check out how it works by copying this project.
4. Using an Ill-sized Valve in Your System
When selecting the fittings for a hydraulic or pneumatic system, the first step is to determine the size of the valve required. If your valve is undersized (relative to the overall system), you’ll likely face increased system resistance, pressure loss and additional stress, all of which lead to higher costs. On the other hand, if your valve is oversized or designed for a higher flow rate than required, it will be inefficient.
The optimal solution is to design a valve specifically for the conditions it will be placed under. Until now, this has been relatively inaccessible for the large majority of engineers. Limited resources available for testing, the time and expense required in making a working prototype and time pressure during the product development phase have all reduced the uptake of CFD simulation software. With SimScale, this is no longer the case. The easy-to-use, cloud-based simulation tool not only speeds up your product development but saves you resources and time.
5. Failing to Take Into Account Critical Scenarios in Your Valve Design
While using an ill-sized valve may cause problems for you or your customer, a more critical scenario is valve failure. Water hammer effects, high-speed choke, cavitation, and erosion are all terms to be considered when designing a long-lasting high-quality valve. Let’s dive further into a few of these terms and what they mean:
When strong pressure waves travel through a pipe system they can cause a tonal noise not unlike a hammer hitting a wall. This effect is what is generally referred to as a “water hammer”. A “water hammer”, or more generally fluid hammer, occurs when a fluid that is in motion is forced to stop or change direction suddenly, affecting its momentum. If a valve closes too quickly or suddenly within a pipe system, this creates a surge of compression-suction pressure. In mild cases, this will lead to noise or vibration; in major cases, it can lead to total pipe collapse.
“Choke” occurs in a system when flow velocity increases to such an extent that it matches the speed of sound. This causes a shockwave which decelerates flow rate and can cause a blockage in the system. Choke appears most commonly in gas systems, and can generally be avoided with a proper aerodynamic analysis. CFD simulation is an excellent tool to check for localized regions of high speed, and through these results optimize the geometry for improvements.
Cavitation — Noise, Erosion, and Damage
Cavitation is the formation of bubbles or cavities in a fluid due to areas of relatively low pressure. As these cavities implode or collapse further down the stream, they cause shock waves, leading to noise, erosion and in some cases, significant damage.
Although the physics involved in all of these phenomena are extremely complex, and it is difficult to remove the risk entirely, it is relatively easy to reduce the probability of their occurrence with CFD simulation. By analyzing the flow throughout your valve design and identifying low pressure and high-speed regions, you can quickly optimize and iterate your geometry, allowing you to put the optimal design forward into physical prototype production.
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