**Abstract:**
This paper presents the working principle of a self-operated differential pressure control valve and explores its application in protecting cold and heat sources as well as in district heating systems. The valve is designed to maintain a constant pressure difference across its inlet and outlet, ensuring stable operation in various heating and air conditioning projects. Keywords: self-operated pressure control valve, cold and heat source protection, central heating.
**Introduction**
A self-operated differential pressure control valve is a device that regulates the pressure drop across a branch or user in a system, maintaining a consistent pressure level. Unlike traditional valves, it does not require external power or control signals. Instead, it adjusts its opening based on the pressure difference between the inlet and outlet, allowing it to automatically maintain a set pressure. This type of valve is widely used in heating and HVAC systems, particularly in metered heating projects where precise flow regulation is essential. This article focuses on the functionality of self-operated differential pressure control valves and their role in both cold/heat source protection and central heating applications.
**1. Structure and Working Principle**
The ZY47-16C self-operated differential pressure control valve serves as a typical example. It consists of a spring, a pressure-sensitive diaphragm, and a stem, all integrated into a single unit. The outlet pressure (P2) is introduced into the upper chamber of the diaphragm through a pilot tube, while the inlet pressure (P1) acts on the lower side. The spring is pre-compressed according to the desired pressure difference (ΔPs), ensuring that the force exerted by the spring balances the pressure forces on the diaphragm when the system is in equilibrium.
The valve operates in two main states: closed and open. When the actual pressure difference (ΔP) is less than the set value (ΔPs), the valve remains closed, acting as a shut-off valve. If ΔP exceeds ΔPs, the diaphragm overcomes the spring force, lifting the valve plug and allowing flow. As the valve opens, the pressure difference gradually reduces until it matches the set value. In an open state, the valve continuously adjusts its position to maintain a nearly constant pressure difference, even as system conditions change. By carefully selecting the spring characteristics, the deviation between ΔP and ΔPs can be kept within acceptable limits, typically around 10%.
**2. Application in HVAC Projects**
**2.1 Protection of Cold and Heat Sources**
In modern heating and cooling systems, especially those with metering, user demand for flow regulation has increased significantly. Variations in hot water usage throughout the day can cause fluctuations in system flow, potentially leading to issues such as boiling in fuel or gas units or freezing in chiller evaporators. To prevent these problems, self-operated differential pressure control valves are installed in bypass lines.
When the system flow decreases due to user adjustments, the pressure difference before and after the valve increases. Once this difference exceeds the set value, the valve opens, increasing the flow through the cold or heat source to ensure safe operation. This ensures that the flow through the source remains stable, protecting the equipment from damage. Compared to electric differential pressure control valves, which rely on electrical signals and are more complex and costly, self-operated valves offer greater reliability and lower maintenance costs.
**2.2 Central Heating Systems**
In district heating systems, buildings at different elevations often face conflicting pressure requirements. For instance, low-rise buildings may experience excessive pressure, while high-rise buildings may suffer from insufficient pressure. Self-operated differential pressure control valves help resolve this issue by dividing the network into sections with controlled pressure differences.
For example, in a system where the heat source is located at a lower elevation, a pressurizing pump and a self-operated differential pressure control valve are installed along the return line. During operation, the valve maintains a constant pressure difference, ensuring that the pressure at the front of the network is sufficient for low-rise buildings, while the pressure at the rear meets the needs of high-rise buildings. When the system is not in use, the valve closes, isolating the two sections and maintaining pressure stability. Similar configurations apply when the heat source is at a higher elevation, with the valve placed appropriately to manage pressure distribution effectively.
**3. Conclusion**
Self-operated differential pressure control valves play a crucial role in maintaining system stability in heating and HVAC applications. Their ability to automatically adjust pressure without external power makes them highly reliable and cost-effective. They are particularly effective in protecting cold and heat sources from flow fluctuations and in managing pressure differences in multi-level heating systems. With their simple design and robust performance, these valves are an essential component in modern heating infrastructure.
**References**
He Ping, Sun Gang. *Heating Engineering*. Beijing: China Building Industry Press, 1993.
HLM Powder Coating CO,.Ltd , https://www.holymepowder.com