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Contamination Happens—But Not All Valves Handle It the Same Contamination is an unavoidable part of any mechanical system. In HVAC applications especially, fine particles are almost always present. Even with strainers in place, these tiny contaminants can pass through and pose a threat to sensitive components—particularly flow control valves. For most valves on the market, that’s a problem. Small debris can interfere with internal mechanisms, leading to clogging, jamming, and inconsistent flow. But the Hays Mesurflo® is designed differently. Thanks to its unique, no-sliding-parts construction, the Mesurflo® resists the kinds of failures that often plague traditional valves. Instead of seizing up under stress, it keeps working—delivering consistent, reliable performance even in systems where fine particulate contamination is unavoidable. Why Small Particles Matter More The purpose of this testing was to evaluate how automatic flow control valves perform in systems where a strainer is already installed. In real-world HVAC systems, strainers are standard, and they do a good job of blocking larger debris. So, this evaluation focused specifically on how valves handle smaller particulates that manage to slip through—materials like fine iron filings and oxides. Larger particles were not included in this study, for a good reason. Even in systems where such debris is present, large particulates tend to settle quickly. They don’t travel far, and they don’t circulate easily. This is because the movement of particles through a fluid system is heavily influenced by what’s known as the Reynolds Number—a calculation tied to the size (hydraulic diameter) of the particle and the characteristics of the fluid flow. According to Stoke’s Law, when the Reynolds Number is low (at or below 1), the drag force on a particle increases as the Reynolds Number decreases. This has been confirmed by experimental data and helps explain what happens in HVAC systems: smaller particles, which experience more drag, stay suspended in the flow and move throughout the system. Larger particles, with lower drag, tend to fall out of circulation more quickly. That’s why small contaminants—despite being nearly invisible—pose one of the greatest risks to flow control reliability. And that’s the kind of challenge this test was designed to address. When Flow Controllers Fail: What We Found in the Lab To better understand how automatic flow controllers perform under contaminated conditions, we set up a controlled lab test to simulate real-world HVAC system challenges. Using a custom-built open-loop system, we introduced iron filings and iron oxides into a 1 gallon-per-minute water stream at controlled rates of either 0.8 or 3.6 ounces per hour. At the end of the system, a filter collected the particulates, while the valve under test was installed just before this outlet. We varied the inlet pressure from 5 to 30 PSID and monitored water flow closely. The results were striking. Spring valve failure caused by one contaminant particle. Every single spring-loaded valve tested failed—many within the first few cycles. The culprit? Tiny iron particulates jamming the sliding members inside the valves. These spring valves rely on extremely tight internal clearances to function at high pressures. That precision, while necessary for performance, leaves little room for error—or debris. In fact, it took as little as one contaminant particle to stop the flow regulation entirely. In several cases, the amount of debris that caused failure was so small it couldn’t be measured. The mode of failure was consistent: particles lodged in the tiny gaps between the valve’s moving and fixed parts, locking them in place. And when the tests continued beyond the initial failure point, additional buildup occurred. Because these valves don’t open up significantly at lower pressures, more particulates gathered and further restricted flow, often reducing it to ineffective levels. Mesurflo ® valve maintaining flow despite particulate buildup. In contrast, Hays Mesurflo® performed reliably throughout testing. While some debris did accumulate at the base of the valve—particularly in low-velocity areas—this buildup didn’t impair functionality. That’s thanks to the Mesurflo’s unique design, which features no sliding parts and a generous opening between the orifice and diaphragm. During the low-pressure portions of the test, trapped particles were able to pass through and flush out naturally. Even at the higher contaminant rate of 0.8 oz/hr, the Mesurflo maintained accurate flow control throughout. SUPPORT For additional information or questions on the content of this article, please contact Hays Customer Service at 1-800-354-4297.