Single Offset vs Double Offset vs Triple Offset Butterfly Valve

Butterfly valves are one of the most commonly used types of industrial valves, primarily employed in industries such as water treatment, environmental engineering, chemicals, building plumbing, food processing, and pharmaceuticals etc. When selecting butterfly valves for actual operating conditions, many users find it challenging to choose between single-offset, double-offset and triple-offset butterfly valves, as they are unfamiliar with their structural characteristics and selection criteria. To assist users in making informed selections and gaining a better understanding of these valves, the following information is provided for reference and learning.

1. Single-Offset Butterfly Valves Introduction

Valve stem axis offset design: By offsetting the valve stem centerline from the geometric center of the butterfly plate, the rotation trajectory of the butterfly plate avoids the area of maximum force on the valve seat, effectively alleviating the sealing surface compression issues common in traditional butterfly valves.

Typical application scenarios: Primarily used for flow regulation in medium to low-pressure conditions, commonly found in municipal water supply systems and chemical medium transportation pipelines, with operating pressures typically not exceeding PN16.

2. Double Offset Butterfly Valves Introduction

Composite Axis Offset Mechanism: Building on the single-offset design, a secondary offset of the valve stem relative to the pipeline axis is added, forming a conical seal structure. When opened, the butterfly plate undergoes radial displacement, enabling rapid separation of the sealing surfaces.

Performance Advantages: Sealing pressure is reduced by approximately 40%, and service life is improved by 2-3 times compared to single-offset structures, making it particularly suitable for applications requiring frequent operation, such as power plant circulating water systems.

3. Triple Offset Butterfly Valves Introduction

Three-Dimensional Spatial Offset Design: In addition to the double eccentric features, the valve seat cone angle is offset (typically 8-12°), forming a metal hard seal structure. The contact surfaces use multi-layer stainless steel + graphite composite materials to achieve zero leakage.

High-temperature and high-pressure adaptability: It can withstand 425°C steam media and PN100 pressure ratings, making it indispensable in critical applications such as catalytic cracking units in refineries and main steam isolation valves in nuclear power plants.

4. The Three Valve Types Comparison

Sealing grade differences: Single-eccentric structures typically achieve ANSI Class IV, double-eccentric structures can reach Class VI, and triple-eccentric structures can achieve Class VI zero leakage.

Economic Considerations: The procurement cost ratio is approximately 1:1.8:3.2, but the total lifecycle cost must be evaluated comprehensively, taking into account maintenance frequency and downtime losses.

Medium Adaptability: Triple-offset structures can handle media containing solid particles, double-offset structures are suitable for clean fluids, and single-offset structures have the highest requirements for medium purity.

This article is provided by ZZJG Valve engineer, If you need more information of single offset, double offset and triple offset butterfly valve, please contact us via Email and Whatsapp.