Triple-Offset Butterfly Valves: When Standard Valves Aren't Enough

A standard butterfly valve is a simple, light and economical way to control or isolate flow in a large line. But its rubber seat limits pressure and temperature, and the disc drags against the seat as it closes. When service gets tougher, engineers turn to triple-offset designs.

What the three offsets are

1. First offset. The shaft sits behind the sealing surface, not in the middle of it, so the seal is continuous around the disc.

2. Second offset. The shaft is moved off the centreline of the pipe, so the disc lifts away from the seat quickly when it opens.

3. Third offset. The sealing surface is shaped as an angled cone. The disc swings in a cam-like action and only meets the seat at the final moment of closing.

The third offset is the key. Because there is no rubbing between disc and seat during travel, the metal seal lasts, and the valve can seal tightly without rubber.

What that gives you

• Metal-to-metal seating that tolerates higher temperatures and pressures than resilient seats.

• Tight shut-off in the closed position, often to bubble-tight leakage classes when the design and test standard require it.

• Low wear, so the seal holds up over many cycles.

• Compact, lighter bodies compared with gate and ball valves of the same size.

Where they fit

Typical uses include isolation in process and pipeline facilities, hydrocarbon services, steam and high-temperature lines, and applications where fire-safe design is required. They are less suited to heavy slurries or fluids that leave deposits on the seat.

How to specify one

Give your supplier the size, pressure class, temperature, fluid, seat and body materials, required leakage class and the governing standard, together with end connections (wafer, lug or flanged) and actuation. Different manufacturers' designs vary, so the datasheet should lead.

We supply triple-offset butterfly valves as part of our valve range. Send us your datasheet and we will source to it.