**Abstract:** This paper presents the working mechanism of a self-operated differential pressure control valve and explores its application in protecting cold and heat sources, as well as its role in district heating systems. The focus is on how these valves maintain stable pressure conditions and enhance system efficiency.
**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 branch or user’s network, ensuring that it remains relatively constant. Unlike traditional valves, this type of valve adjusts its opening based on the pressure difference between the inlet and outlet, maintaining a consistent pressure drop without external power sources. These valves are widely used in heating and air conditioning projects, particularly in metered heating systems where precise pressure control is essential. This article provides an overview of the function and operation of such valves, highlighting their importance in HVAC applications.
**1. Structure and Working Principle**
To illustrate the working principle, we take the ZY47-16C self-operated differential pressure control valve as an example. As shown in Figure 1, the valve consists of a spring, a pressure-sensitive diaphragm, and a stem. The outlet pressure (P2) is introduced into the upper chamber of the diaphragm through a pressure guide tube, while the inlet pressure (P1) acts on the lower side. The spring is pre-compressed according to the set pressure difference (ΔPs), which is the desired pressure drop between P1 and P2. When the actual pressure difference (ΔP) exceeds ΔPs, the diaphragm overcomes the spring force, causing the valve to open and adjust the flow to restore balance.
The valve operates in two main modes: closed and open. In the closed state, if ΔP is less than ΔPs, the valve remains shut. If ΔP exceeds ΔPs, the valve opens to allow more flow, reducing the pressure difference. In the open state, the valve continuously adjusts its opening to maintain ΔP close to ΔPs. This ensures that the pressure before and after the valve remains stable, regardless of fluctuations in system demand.
**2. Application in HVAC Projects**
**2.1 Protection of Cold and Heat Sources**
In modern heating systems, especially those involving fuel or gas units, proper flow regulation is crucial to prevent damage. For example, if the flow through a chiller unit is too low, it can cause freezing in the evaporator, leading to equipment failure. Similarly, reduced flow in a boiler may result in overheating and potential damage.
To address this, a self-operated differential pressure control valve is often installed in the bypass line. When the system flow decreases, the pressure difference across the valve increases, triggering it to open and increase the flow through the cold or heat source. This helps maintain a minimum required flow, ensuring safe and stable operation. Compared to electrically controlled valves, self-operated versions are more reliable and cost-effective, making them a preferred choice for system protection.
**2.2 Use in Central Heating Systems**
In district heating projects, buildings at different elevations pose challenges in maintaining consistent pressure. Lower buildings may experience excessive pressure, while higher ones may face underpressure or air pockets. A self-operated differential pressure control valve can effectively manage these issues by balancing the pressure across different parts of the network.
For instance, in a system where the heat source is located at a lower level, a pressure pump is installed in the supply line, and a differential pressure control valve is placed in the return line. During operation, the valve maintains a constant pressure drop, allowing the system to meet the needs of both high-rise and low-rise buildings. When the system is not running, the valve closes, isolating sections of the network and ensuring pressure stability.
**3. Conclusion**
Self-operated differential pressure control valves are effective tools for maintaining stable pressure in heating and cooling systems. They automatically adjust their opening based on the pressure difference, ensuring that the system operates efficiently and safely. Compared to traditional electric valves, they offer greater reliability and lower costs, making them ideal for protecting cold and heat sources.
Moreover, these valves play a critical role in addressing pressure differences in central heating systems, helping to balance the needs of buildings at varying heights. Their ability to maintain consistent pressure makes them an essential component in modern HVAC projects.
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