**Abstract:** Based on the analysis of fluid noise and field investigations after the installation of flow control valves, we developed a low-noise product by applying the principles of flow velocity, pressure differential, and multi-stage noise reduction. The key factors in noise generation include cavitation, turbulent flow, and improper system design. This paper presents our experience and technical improvements in reducing noise, particularly in heating systems. **Keywords:** Noise source, liquid flow rate, cavitation noise, monomer flow rate, multi-stage noise reduction Our leading product—self-operated flow control valve—has been in use since 1993, marking over a decade of development. During this time, it has gradually gained recognition within the heating industry. Initially, users had limited understanding of its application, often using it in a one-sided manner. However, through continuous improvements, the valve has proven effective in various applications. Over the past ten years, we have made two major upgrades. From 1993 to 1998, we introduced Type II valves, but due to their large size and limited installation space, we made significant modifications in 1999. This improved version allowed for installation at any angle and reduced the volume by 40%. In the following five years, from 2002, users reported increased noise, especially in outdoor overhead pipelines. To address this, we conducted extensive research and testing, resulting in a low-noise, adjustable, and lockable flow control valve. The noise level was reduced from 65–75 dB to 45–55 dB, meeting diverse user needs. In the development process, we learned several important lessons that we now share with colleagues for reference. **First, noise source analysis** In heating systems, pumps, pipes, and valves are essential components, but they also contribute to noise. When liquids flow through pipes, turbulence and friction generate pressure disturbances, especially when the Reynolds number (Re) exceeds 2400, leading to turbulent flow. This turbulence can be inherently noisy. When turbulent flow interacts with throttling valves or abrupt pipe sections, additional noise is generated. Valves, particularly throttle or pressure-limiting valves, are the main sources of noise in liquid transmission. If the flow velocity is high enough and the valve is partially closed, a choke area forms, increasing the flow rate and decreasing the internal pressure. If the velocity reaches or exceeds the critical velocity of the medium, bubbles may form. As these bubbles move downstream and collapse, they cause pressure fluctuations, known as cavitation, which results in cavitation noise. Cavitation noise is proportional to the seventh or eighth power of the flow rate. Therefore, even small changes in flow can significantly impact noise levels. To reduce this, multi-stage valves are used to gradually lower the flow and pressure, minimizing the risk of cavitation. **Second, flow rate and pressure-related noise survey** We conducted field tests at a heating station in Tianjin, covering an area of 265,000 square meters. Some buildings, such as Building 34 and the Spring Breeze area, reported high noise levels. Measurements showed indoor noise levels reaching up to 60 dB, while others were around 45–47 dB. Despite flows not exceeding design limits, the individual flow rates were too high, leading to large pressure drops and cavitation noise. The pressure difference in Building 34 was 0.06 MPa, compared to 0.02 MPa in other areas. This imbalance caused uneven pressure distribution, resulting in higher noise levels. To resolve this, we adjusted the main branch valve and unit door valves, reducing the pressure drop and flow rate. After retesting, noise levels dropped significantly, meeting user requirements. **Third, noise-reducing control valve development** From theoretical analysis and field data, we concluded that noise is closely related to flow rate and pressure. Using the formula △Lw = 60lg(V), we designed a multi-stage noise reduction structure. The first stage involved replacing the manual valve with an inclined screw plug to reduce flow. The second stage used a double-arc, double-valve structure to slow down the fluid flow. The third stage further reduced the speed through another arc surface. Additionally, side ribs were added to the automatic valve flap to prevent bubble formation. After nearly 1,000 tests, we successfully reduced the noise level from 65–75 dB to 45–55 dB. These improvements expanded the valve’s application range. Today, our noise-reducing valves are mass-produced, with over 10 customers placing orders. With a typical lifespan of 30–50 years, self-operated flow control valves have become a standard product in China. Our goal is to educate users on proper application and continue developing new products to better serve the heating industry.

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