Many industries use multi-stage orifice assemblies to restrict flow and reduce line pressures. These devices can produce large pressure drops, while avoiding the noise and cavitation issues that single-stage orifice plates can create. With no moving parts, these devices are critical in industries such as oil and gas, LNG, and Nuclear—where the utmost accuracy, system reliability, and maintenance reduction are requirements.

Sulzer, a leading fluid engineering company that specializes in pumping, agitation, mixing, separation and application technologies for fluids of all types, needed a qualified orifice design to meet their client’s specific process requirements. Based on previous work, they knew Alden was the right team to design and qualify a multi-stage orifice design to meet the stringent pressure drop needed.

The application:

Sulzer needed a qualified multi-stage orifice to be used as a minimum flow orifice assembly for an auxiliary feedwater pump for a nuclear industry power plant. Using up to 7-stages in a multi-stage orifice assembly would provide optimum process performance in a compact design, while eliminating the need for regular maintenance.

The approach: 

Our engineers approached this process like we do for all our design engineering, testing, and qualifications — by first working with the client to understand the process, flow and pressure requirements needed for the design. Sulzer provided these input conditions based on their clients needs, which Alden used to construct a computational fluid dynamics (CFD) model. The computational model provided a preliminary basis of design, while allowing small changes to be made quickly and cost-effectively. 

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The computational model was iterated upon until the required conditions were met. This provided the basis for the construction of a physical prototype. Because CFD models are run based on an idealized model and inputs, they do not always accurately reflect true-to-life performance. Physical testing reveals issues with the design that are difficult to predict computationally; in particular, noise and cavitation are phenomena that cannot be accurately predicted in CFD.

Alden manufactured the orifice assembly from stainless steel on site — an advantage that expedited the initial manufacturing and subsequent design iterations. The orifice assembly was tested using the specific flow, temperature, and pressure requirements provided by Sulzer. Data collected from high-accuracy laboratory equipment was analyzed, which informed design iterations to approach the finalized design. Small modifications to the flow geometry can yield large effects to the pressure drop across the assembly, so it was critical to approach the design modifications conservatively. By analyzing the data as testing is being performed, design iterations can be made intelligently, which reduces the number of tests required to achieve the final iteration.


The multi-stage orifice assembly was tested under Alden's Quality Assurance program with a QA documented and qualified test that demonstrated the proper differential pressure behavior, as well as the lack of cavitation at the conditions of interest


Once the iterations produced a design that met Sulzer’s strict flow requirements, the multi-stage orifice design was qualified under Alden's stringent quality assurance (QA) program. This qualification testing demonstrates the orifice is designed for the proper differential pressure, flow, and temperature conditions, while avoiding cavitation and excessive noise. All factors that could affect the qualification are rigorously documented and reviewed, including instrumentation calibration, data analysis and review, and reporting.

The test report provided the geometric details required for successful manufacture of the multi-stage orifice design. Since multi-stage orifice assemblies are extremely sensitive to small geometry changes, strict manufacturing tolerances were provided to ensure the final manufactured design would meet the desired flow requirements. These manufacturing tolerances were informed through the iterative testing, which provided quantitative insight into the effect each geometric parameter has on the overall function of the design. This allowed tolerances to be strict where required, but conservative where allowable, such that manufacturing costs in the final design would not be unnecessarily high.

The Results

Alden's tiered design approach allowed the efficient design, testing, and qualification of a multi-stage orifice assembly that met Sulzer's strict process requirements. By starting with a computational model, an initial design was reached quickly and cost-effectively. Physical testing allowed for the most accurate and realistic representation of end-use conditions. On-the-fly analysis of data throughout testing informed design decisions to drive the assembly toward the final design. The testing and qualification was performed under Alden's 10CFR50 Appendix B Quality program, ensuring the final experimental verification met the stringent quality requirements our clients expect. 


I knew that Alden would be able to provide the necessary design to meet our client's strict condition requirements. It was a no brainer to contact them for help and it was a pleasure to work with them

Art Washburn, Project Manager, Sulzer