What Is a Concentric Butterfly Valve?
A concentric butterfly valve is the most classic and widely used type of soft-seated butterfly valve. The term “concentric” means that the centerline of the valve stem, the center of the disc, and the centerline of the valve body are all aligned on the same axis.
During operation, the disc rotates 90° around this central axis, functioning like a circular plate inside the pipeline that opens or blocks the flow.
The key advantages of this design are its symmetry, compact structure, reliable sealing, and reasonable cost. Because it uses a soft seat, a concentric butterfly valve is ideal for water systems, HVAC, circulating water, and general service applications where tight sealing is required but the pressure and temperature are not high.
Key Components of a Concentric Butterfly Valve
To understand why the concentric butterfly valve performs so reliably in water systems, it helps to look at its internal structure.
Elastic Soft Seat
Concentric butterfly valves almost always use soft seating materials such as EPDM (for potable and hot/cold water service), NBR (for better oil resistance), or Viton (for higher temperature capability).
Main function: To provide sealing. When the valve closes, the disc compresses the rubber seat, creating elastic deformation that achieves tight, zero-leakage sealing.
Disc
The disc is the circular plate located in the center of the pipeline, commonly made of ductile iron with a nickel-plated surface.
Main function: To control flow. The nickel-plated surface is smooth, minimizing friction against the rubber seat. This results in easier operation and significantly extends seat life.
Stem (Shaft)
The stem passes through the center of the disc and connects to the handle, gear operator, or actuator.
Main function: To transmit torque. Dual O-rings are often used for sealing to prevent leakage around the stem.
Concentric Symmetry (the “Concentric” Principle)
The centerlines of the stem, disc, and valve body are aligned.
Main function: This symmetrical rotation ensures smooth torque, easy operation, and stable sealing performance.
Operating Principle of a Concentric Butterfly Valve
The operating principle of a concentric butterfly valve is straightforward: the disc rotates 90° around the stem to open or close the flow.
When the disc is aligned parallel to the direction of flow, the valve is fully open and fluid passes through with minimal resistance.
When the disc rotates 90° to a position perpendicular to the flow, the valve is fully closed. At this point, the edge of the disc presses against the soft rubber seat inside the valve body.
The elastic deformation of the seat tightly wraps around the disc edge, cutting off the flow and achieving reliable sealing.
Why Concentric Butterfly Valves Are Ideal for Water Systems
Water systems—such as municipal supply, HVAC, and circulation loops—typically operate at normal temperatures, low to medium pressures, and use water as the working medium. The design of the concentric butterfly valve aligns perfectly with these conditions.
1) Excellent Sealing Performance
Water systems demand zero leakage.
The soft rubber seat in a concentric butterfly valve provides reliable bi-directional sealing even at low pressure, fully meeting sealing requirements.
2) Significant Cost Advantages
Water systems involve long pipeline networks and a large number of valves, making cost a critical factor.
A concentric butterfly valve has a simple structure, helping reduce procurement, installation, and maintenance costs compared to alternative valve types.
3) Lightweight Operation for Frequent Use
Valves in water systems are often opened, closed, or adjusted regularly.
Thanks to its symmetric design, the required operating torque is very low, making manual operation easy and actuator automation straightforward.
4) Low Flow Resistance and Energy Savings
When fully open, the disc causes very little obstruction to the flow.
This results in lower pressure drop compared to gate or globe valves and contributes to reduced pumping energy consumption.
Difference Between Concentric and Eccentric Butterfly Valves
Choosing between a concentric and eccentric butterfly valve depends on the operating conditions and performance requirements.
The fundamental difference lies in whether the valve stem shares the same centerline with the disc and the pipe.
Comparison Item | Concentric Butterfly Valve | Eccentric Butterfly Valve |
Structure | The stem, disc, and pipeline centerlines are fully aligned. | The stem and disc are offset from the pipeline centerline. Double eccentric has two offsets; triple eccentric adds a conical sealing offset. |
Sealing Principle | Compression sealing: the disc presses directly against the rubber seat, sealing through elastic deformation. | Position sealing: the disc engages tightly against the metal seat at a specific angle, with minimal friction. |
Seat Material | Soft elastomeric materials (EPDM, NBR). | Metal or composite hard materials (e.g., stainless steel + graphite). |
Advantages | Simple design, lower cost, excellent sealing at low pressure, low operating torque. | Handles high temperature and pressure, wear-resistant, long service life, capable of achieving high integrity (zero) leakage. |
Limitations | Not suitable for high temperature or high pressure; rubber seat may age or wear. | Higher cost, more complex structure, heavier weight. |
Typical Applications | Water systems (municipal supply, HVAC, firewater). | Severe conditions (steam, oil & gas, chemical process, high-temp hot water, power plants). |
Simple Selection Principle
Choose a concentric butterfly valve when operating at ambient temperature and low pressure, and when cost-effectiveness and practicality are priorities, especially for water or neutral fluids.
Choose an eccentric butterfly valve when the application involves high temperature, high pressure, corrosion, abrasion, or requires extremely tight (zero-leakage) sealing.
Frequently Asked Questions (FAQ)
Can a concentric butterfly valve be used for steam service?
No. Soft-seated materials such as EPDM are not suitable for steam (typically limited to ≤120°C).
High temperature causes rapid hardening and cracking of the seat, leading to sealing failure.
For steam pipelines, a metal-seated eccentric butterfly valve or a globe valve should be used.
How do I choose the right seat material — EPDM or NBR?
It depends on the medium.
EPDM: Best for hot water, chilled water, potable water, and HVAC applications. It has excellent aging resistance.
NBR: Better oil resistance. Recommended for industrial water systems containing lubricants, fuels, or hydraulic oils.
What is the maximum pressure rating for a concentric butterfly valve?
Typically PN10 or PN16 (10 or 16 bar).
This limitation comes from the soft seat material and the overall valve design. Always ensure that the system pressure does not exceed the valve's rated pressure.
Can a concentric butterfly valve be used for flow control?
Yes, but only for coarse regulation.
Between approximately 40° and 90° open, it offers reasonable throttling characteristics.
For precise flow modulation, a purpose-designed control valve is recommended.
Conclusion
Thanks to its soft-seated design, easy operation, cost advantages, and strong suitability for water-related applications, the concentric butterfly valve has become the preferred choice in municipal water supply, HVAC, circulation loops, and similar systems. When the seat material is selected correctly and the pressure/temperature conditions are properly matched, it delivers reliable performance and long service life.
If you are looking for concentric butterfly valves that meet international standards and offer reliable sealing and smooth operation, TFW Valve provides a full range from DN50 to DN1600. We can also recommend the most suitable configuration based on your operating conditions. As a professional butterfly valve manufacturer, we focus on consistent quality and ongoing technical improvements to help ensure safe and dependable pipeline performance.
If you have any questions or need engineering support, please feel free to contact us.
