**Abstract:** This paper presents the operational 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 focus is on how these valves maintain stable pressure conditions and enhance system efficiency in HVAC projects.
**Keywords:** Self-operated differential pressure control valve, cold and heat source protection, central heating
**0. Introduction**
A self-operated differential pressure control valve is designed to regulate the pressure within a specific branch or user section of a system, ensuring that the pressure remains relatively constant. Unlike traditional valves, it adjusts its own opening based on the pressure difference across it, allowing for automatic regulation without external power sources. These valves are widely used in heating and air conditioning systems, particularly in metered heating projects where precise control is essential. This article highlights the unique function of such valves, their working mechanism, and their role in improving system performance and safety in HVAC applications.
**1. Structure and Working Principle**
To illustrate the operation of a self-operated differential pressure control valve, we take the ZY47-16C model as an example. The valve consists of a spring, a pressure-sensitive diaphragm, and a stem, all connected together. The outlet pressure (P2) is introduced into the upper chamber of the diaphragm via a pressure-tapping tube, while the inlet pressure (P1) acts on the lower side. The spring is pre-compressed according to the set pressure difference (ΔPs), which ensures that the force exerted by the spring matches the force from the pressure difference under normal conditions.
The valve opens when the actual pressure difference (ΔP) exceeds the set value (ΔPs). As the valve opens, the flow increases, reducing the pressure difference until it stabilizes around ΔPs. If the pressure difference drops below ΔPs, the valve closes, maintaining a consistent pressure drop. This self-regulating mechanism allows the valve to operate efficiently over a wide range of flow conditions, making it ideal for complex heating and cooling systems.
**2. Applications in HVAC Projects**
**2.1 Protection of Cold and Heat Sources**
In modern heating systems, especially those using fuel or gas units, maintaining a minimum flow rate is crucial to prevent damage caused by partial boiling or freezing. For instance, if the flow through a chiller unit becomes too low, it may lead to pipe freezing, potentially causing serious equipment failure.
To address this, a self-operated differential pressure control valve can be installed in the bypass line. When the system flow decreases, the pressure difference across the valve increases, triggering it to open and redirect flow back to the heat source. This ensures that the heat source always receives enough flow to operate safely. Compared to electrically controlled valves, self-operated versions are more reliable and cost-effective, as they do not require external power or signal transmission.
**2.2 Application in Central Heating Systems**
In district heating projects, buildings at different elevations often face conflicting pressure requirements. Lower buildings may suffer from excessive pressure, while higher ones may experience insufficient pressure, leading to issues like radiator damage or emptying. A self-operated differential pressure control valve can effectively balance these conditions.
For example, in a system with a heat source located at a lower level, a pressurizing pump and a differential pressure control valve can be strategically placed along the water supply and return lines. During operation, the valve maintains a constant pressure drop, dividing the network into two sections: one with lower pressure for low-rise buildings and another with higher pressure for high-rise structures. When the system is inactive, the valve automatically closes, isolating the two parts and ensuring stable pressure distribution.
**3. Conclusion**
A self-operated differential pressure control valve operates by adjusting its opening based on the pressure difference between its inlet and outlet. It remains closed when the pressure difference is below the set value and opens when it exceeds it, ensuring a stable pressure drop across the valve.
These valves offer significant advantages in protecting cold and heat sources, compared to traditional electric control systems, by providing reliable and cost-effective pressure regulation. Additionally, they are highly effective in resolving pressure conflicts in district heating systems, especially in areas with varying building heights. Overall, self-operated differential pressure control valves play a vital role in enhancing the efficiency, stability, and safety of HVAC systems.
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