Self-operated Differential Pressure Valve

Self-operated differential pressure valve is an automatic hydraulic control component widely adopted in central air conditioning, floor heating and district heating circulating water systems. Distinguished from electrically driven pressure control valves, it relies entirely on medium pressure inside pipelines as power source, without external power supply, actuators or any electrical control accessories. Its core function is to automatically maintain a constant differential pressure between the supply and return pipes of each branch loop, isolating pressure fluctuations from main pipelines and providing stable operating conditions for downstream balancing valves, fan coils and heating terminals.

The complete internal structure consists of a pressure sensing diaphragm, precision throttling plug, balance spring, sealed valve body and two external impulse pressure sampling tubes. These sampling pipes are separately connected to the upstream supply pipeline and downstream return pipeline of the controlled loop to transmit real-time pressure signals to both sides of the diaphragm. Before system formal operation, construction workers rotate the external adjustment handwheel to pre-set the target differential pressure value according to hydraulic design requirements, and lock the position to avoid accidental shifting.

During normal operation, when the pressure of main pipes rises due to variable frequency pump operation or shutdown of partial branch terminals, the actual differential pressure across the loop will exceed the preset standard. The pressure difference pushes the sensing diaphragm to compress the built-in balance spring, driving the throttling plug to reduce the effective flow area and throttle excess pressure. Conversely, if main pipe pressure drops and loop differential pressure becomes insufficient, the rebound force of the spring pushes the diaphragm backward to open the flow channel wider and supplement pressure. The whole adjustment cycle runs automatically and continuously, keeping the differential pressure of the controlled loop stable within the calibrated range all the time.

The valve body is mostly cast from high-strength ductile iron with anti-rust epoxy coating to resist long-term erosion of hot and chilled circulating water. Key moving parts including the diaphragm and sealing rings adopt aging-resistant EPDM, while the throttling plug uses stainless steel to prevent jamming, scaling and internal leakage under years of continuous running. Standard pressure ratings PN10 and PN16 cover mainstream engineering demands, with threaded, flange and grooved connection ends ranging from DN15 to DN300. Small threaded models match fan coil and floor heating manifold branches, while large flanged specifications serve vertical risers and heat exchange station distribution mains. Every finished valve undergoes strict factory calibration to guarantee high control accuracy within the full working pressure range.

Compared with electrically powered differential pressure control valves, this self-operated version brings prominent cost and safety advantages. It requires no wiring, controllers or signal cables, greatly simplifying on-site construction procedures and cutting material and labor costs. Without electrical parts inside, it eliminates hidden dangers such as circuit short circuit, electric leakage and electrical component failure, making it suitable for humid equipment rooms and unattended pump stations. It also avoids extra energy consumption for driving actuators, helping reduce the overall operation cost of HVAC systems.

In unbalanced water networks, frequent pressure surges of main pipes will lead to excessive flow, loud pipeline vibration and noise in low-resistance branches, while remote terminals suffer insufficient water volume and uneven indoor temperature. Even with static balancing valves installed, unstable differential pressure will break preset flow parameters. The self-operated differential pressure valve fundamentally solves this problem by stabilizing loop pressure difference independently. It is commonly combined with static balancing valves to form a full hydraulic balance solution for multi-story buildings, shopping malls and residential communities.

Installation is usually arranged on the main inlet pipe of each independent floor, unit or zone loop. After one-time differential pressure setting during system commissioning, no manual adjustment or regular inspection is needed in daily operation. The compact integrated design reduces the number of pipeline fittings and connecting joints, lowering potential medium leakage risks. By optimizing the hydraulic balance of the whole water network, it effectively decreases the operating load of circulating water pumps and improves the energy-saving performance of chillers and heat exchangers.

Core Advantages

Self-powered design driven by medium pressure, no external power supply or electrical control equipment required

Automatically compensates main pipe pressure fluctuations to keep branch loop differential pressure constant

No electrical components, safe and reliable for humid, unattended mechanical equipment rooms

Simple installation without wiring work, saving construction period and engineering investment

Wear-resistant, anti-scaling internal parts support long-term continuous operation with low failure rate

Works cooperatively with static balancing valves to realize full hydraulic balance of heating and cooling water networks

Suppresses pipeline noise and water hammer, balances indoor temperature of all terminals and reduces pump energy consumption

Typical Application Scenarios

High-rise building heating and air conditioning vertical risers, floor heating manifold main pipelines, fan coil unit branch loops, commercial complex multi-zone chilled water systems, residential district heat exchange station distribution pipes and industrial constant-temperature cooling water circulation networks