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Applying them to variable flow operations doesn't just fail to balance the system—it becomes a significant operational burden.

1. Core Principle: Constant Flow vs. Variable Flow

Self-operated flow control valves are designed to maintain a set flow rate regardless of pressure fluctuations. While this is ideal for constant flow "quality adjustment" systems (where only the water temperature changes), it is counterproductive in modern variable flow "quantity adjustment" systems. Once a system transitions to variable flow, these valves actively work against the system’s goals.

2. Failures in Source-Side Variable Flow Regulation

Many heating enterprises implement variable flow at the heat source using Variable Frequency Drives (VFDs) or by adjusting the number of operating pumps. In these scenarios, self-operated flow control valves lead to several critical failures:

Abnormal Flow Compensation at the Near-End: When the system’s total flow decreases and pipe pressure drops, the valves at the "near-end" (users closest to the pump) detect the pressure drop. To maintain the pre-set constant flow, the valve core automatically opens wider.

Dynamic Hydraulic Imbalance: Because near-end valves open up to grab more water, the flow reduction occurs almost entirely at the "far-end" (remote users). The flow does not decrease proportionally across the network.

Starving Remote Users: The "constant flow" at the near-end literally steals heat from the far-end. This results in severe dynamic hydraulic imbalance, leaving remote users with insufficient heat.

3. Conflicts with User-Side Variable Flow Regulation

When a heating network is designed for user-side variable flow (where users adjust their own consumption), self-operated flow control valves create two major issues:

Flow "Ceiling" Effect: When a user needs to increase heat and requires more flow, the valve acts as a restrictor. It locks the flow at the pre-set value, preventing the user from reaching the desired temperature.

System Interference and Power Waste: When a user tries to reduce flow, the self-operated valve’s attempts to regulate cause interference between different branches. In this state, the valve becomes a "useless component" that exists only to consume pump power, significantly lowering the system's energy efficiency.

4. Expert Summary: Correct Strategies for Hydraulic Balance

HVAC Engineering Best Practices:

Engineers must recognize that self-operated flow control valves should never be used in networks where either the source or the user actively varies the flow.

The Wrong Choice: Using self-operated flow control valves in systems with VFDs or multi-pump variable flow configurations.

The Right Choice: Use these valves only in constant-flow systems where only the supply water temperature is adjusted.

The Better Alternative

For high-efficiency, energy-saving variable flow networks, engineers should opt for Self-Operated Differential Pressure Control Valves or Dynamic Balancing Electric Control Valves. These components adapt to complex dynamic conditions, ensuring heat is distributed proportionally without wasting electricity or compromising comfort for remote users.

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2026-01-15

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