Difference between soft seal and hard seal butterfly valve

Soft-seal and hard-seal butterfly valves are classified by their sealing matching structure, with distinct differences in sealing performance, temperature resistance, pressure bearing, applicable media and service scenarios. Engineers must distinguish their features before pipeline procurement to avoid leakage and premature valve failure (Wilson, 2021).

1. Sealing Structure & Materials

Soft-seal butterfly valves adopt elastic non-metal sealing pairs. The valve disc presses tightly against a rubber lining (EPDM, NBR, PTFE) fixed inside the valve body. The flexible rubber compensates machining gaps, achieving bubble-tight zero leakage under nominal pressure.

Hard-seal butterfly valves use metal-to-metal sealing surfaces. Both the valve disc and valve seat are surfaced with alloy materials such as Stellite. There is no elastic cushion; sealing relies on precise machining and sufficient closing torque to compress the metal contact surface. Minor micro-leakage is inevitable under standard test criteria.

2. Temperature & Pressure Adaptability

Soft rubber seals have limited temperature tolerance. Conventional EPDM soft seals only work within -20℃ ~ 120℃, and PTFE lined types can reach up to 160℃. Most soft-seal designs are rated PN10/PN16, rarely suitable for high-pressure industrial processes.

Metal hard seals withstand extreme temperatures ranging from -40℃ to 600℃, and support PN25, PN40, ANSI Class 300/600 high-pressure grades. They remain stable under alternating hot and cold working conditions.

3. Applicable Working Media

Soft-seal valves fit clean, non-abrasive media: tap water, HVAC circulating water, neutral gas, light sewage and low-concentration weak acid and alkali fluids. They cannot endure high-temperature steam, oil with solid particles or abrasive slurry, as particles will scratch the rubber lining and cause permanent leakage.

Hard-seal butterfly valves are designed for harsh media: high-temperature steam, flue gas, petroleum, chemical corrosive fluid, ash water, particle-containing slurry and heat conduction oil. The alloy sealing surface resists abrasion and chemical erosion.

4. Maintenance, Cost & Service Life

Soft-seal valves feature low manufacturing cost, light weight and small operating torque for manual or lightweight pneumatic actuators. However, rubber linings age, swell or harden under heat and chemicals, requiring frequent seal replacement within 1–3 years.

Hard-seal valves have higher raw material and processing costs, demanding larger actuators to provide enough closing torque. Their alloy sealing surface wears slowly; regular maintenance intervals extend to 5–10 years under normal operating conditions.

5. Core Selection Summary

Choose soft-seal butterfly valves for low-temperature clean medium pipelines requiring zero leakage and cost control. Select hard-seal butterfly valves for high temperature, high pressure, abrasive or strongly corrosive industrial pipelines where absolute zero leakage is not mandatory.

1. APA 7th Edition

Wilson, R. (2021). Performance contrast of elastomer and metal seated butterfly valves for industrial fluid control. Process Safety Progress, 40(4), e12768. 

2. MLA 9th Edition

Wilson, Robert. "Performance Contrast of Elastomer and Metal Seated Butterfly Valves for Industrial Fluid Control." Process Safety Progress, vol. 40, no. 4, 2021, e12768, 

3. GB/T 7714-2015 

[1] Wilson R. Performance contrast of elastomer and metal seated butterfly valves for industrial fluid control[J]. Process Safety Progress, 2021, 40(4): e12768.