Soft-Seated vs Metal-Seated Butterfly Valves: Differences and Selection Guide

Sealing Principle

During valve closure, the disc compresses the valve seat, causing the soft sealing material to undergo elastic deformation. This deformation fills the microscopic gaps between the disc and the seat, creating continuous and reliable sealing contact.

Key Advantages

1. Excellent sealing performance: The elastic seat material readily deforms, making it easy to achieve zero leakage.
2. Smooth operation: Low operating torque allows easy opening and closing, well suited for manual operation or small actuators.
3. High tolerance to installation conditions: Requirements for body machining accuracy and pipeline alignment are relatively forgiving.
4. Wide range of applications: Commonly used in water supply and drainage, water treatment, and HVAC systems operating under low to medium pressure.

What Is a Metal-Seated Butterfly Valve?

A metal-seated butterfly valve achieves sealing through precise contact between metal or hard-alloy sealing surfaces. The valve seat is typically made of stainless steel, alloy steel, or hardfaced with wear-resistant alloys to ensure durability and high-temperature resistance. This type of butterfly valve is commonly designed with an eccentric structure to enhance sealing performance and reduce wear during operation.

Sealing Principle

In the final stage of valve closure, the eccentric design brings the disc sealing surface into precise contact with the metal seat at a defined position. Sealing is achieved through metal-to-metal contact and the applied contact force, rather than through elastic deformation of the materials.

Key Advantages

1. High temperature and wear resistance: Metal sealing materials can withstand extreme temperatures and pressures.
2. Stable sealing performance: Sealing reliability is less affected by temperature fluctuations or material aging, offering more consistent performance under varying operating conditions.
3. Long service life: Wear of the sealing surfaces is controllable, making this design suitable for applications with frequent opening and closing.
4. Designed for demanding conditions: Commonly used in industrial piping, steam systems, and other services with more severe operating requirements.

The sealing performance of a soft-seated butterfly valve mainly depends on the elasticity and recovery capability of the seat material. In contrast, the sealing performance of a metal-seated butterfly valve is primarily determined by the soundness of the structural design, the machining quality of the sealing surfaces, and the stability of the contact condition.

Soft-Seated vs Metal-Seated: Key Technical Differences

Note: The temperature and pressure ranges listed above represent typical engineering reference values. Actual selection should be based on the valve design, sealing materials, and the manufacturer’s technical specifications.

How to Choose Between Soft and Metal Seated Butterfly Valves

In practical engineering applications, there is no absolute advantage or disadvantage between soft-seated and metal-seated butterfly valves. The key lies in whether the sealing method is properly matched to the actual operating conditions. By considering the sealing principles and performance characteristics of both designs, selection can be guided by several core factors.

1. Selection Based on Media Type

• When the medium is water, air, or other mild media with minimal corrosion and wear on the valve seat
  → Soft-seated butterfly valve.
• When the medium is steam, high-temperature fluids, or media containing a small amount of solid particles, requiring higher temperature and wear resistance from the valve seat
  → Metal-seated butterfly valve.

2. Selection Based on Temperature and Pressure Conditions

• When operating under normal or moderate temperatures and low to medium pressure, within the safe operating limits of the elastic seat material
  → Soft-seated butterfly valve.
• When operating temperatures are high, temperature fluctuations are significant, or pressure ratings approach or exceed the suitable range of elastic materials
  → Metal-seated butterfly valve.

3. Selection Based on Sealing Performance Requirements

• If the system is sensitive to leakage and requires bubble-tight or zero visible leakage 
  → Soft-seated butterfly valve.
• If the system permits industrial-grade minor leakage but cannot tolerate rapid degradation or sudden failure of sealing performance over time 
  → Metal-seated butterfly valve.

4. Selection Based on Installation and Maintenance Conditions

• When site installation conditions are less than ideal, where machining or alignment errors are difficult to completely avoid, and where ease of sealing assurance and simplified future maintenance are priorities
   → Soft-seated butterfly valve.
• When the system operates continuously for long periods, downtime maintenance costs are high, and the goal is to minimize unplanned replacements 
  → Metal-seated butterfly valve.

5. Selection Based on Operational Mode

• When the valve operates infrequently, with greater emphasis on ease of operation and actuator cost
   → Soft-seated butterfly valve.
• When the valve cycles frequently or operates under significantly fluctuating conditions, with greater emphasis on long-term sealing stability 
  → Metal-seated butterfly valve.

Summary

For mild operating conditions where sealing performance and ease of operation are the primary concerns, a soft-seated butterfly valve is the preferred choice.

For more demanding service conditions where long-term operational stability is critical, a metal-seated butterfly valve is the better option.

The selection between soft-seated and metal-seated butterfly valves should be based on operating temperature, pressure, media characteristics, sealing requirements, and expectations for long-term reliability. A clear understanding of these differences helps prevent premature valve failure and ensures stable system performance.

At Union Valve, we approach every project from actual operating conditions, aligning butterfly valve selection with the specific application requirements. Through well-matched valve designs and configurations, we help our customers achieve long-term, stable operation while reducing operational and maintenance risks over the life of the system. If you have any further questions, please feel free to contact us.

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• EPDM vs PTFE Butterfly Valve Seats: Selection Guide
• Understanding Butterfly Valve Seats: The Differences Between Hard, Soft and Rubber Lined
• Understanding Your Options: Soft Sealing vs Hard Sealing Butterfly
• How to Replace a Butterfly Valve Seat