Triple-offset butterfly valves: when they beat gate and ball valves
Triple-offset valves are used on steam, hot water, petroleum products and gas, where an ordinary rubber-lined butterfly valve cannot take the temperature. They are lighter and faster than gate valves but must be specified correctly.
TAZ Engineering Team · · 6 min
What the three offsets are
First, the shaft sits behind the sealing plane. Second, the shaft is offset from the pipe centreline. Third, the axis of the conical seat is inclined to the pipe axis. The disc touches the seat only at the moment of closing, without rubbing during rotation, so the metal-to-metal seal wears far more slowly than in a concentric valve.
Where they are used
Steam lines and boiler houses, high-temperature district heating, oil terminals and loading racks, gas and chemical plants. The quarter-turn operation suits frequent cycling and automation.
Limits
Many designs have a preferred flow direction, and tightness against reverse pressure may be lower. The disc stays in the bore, so resistance is higher than in a full-bore gate valve and the line cannot be pigged. Abrasive media with solids accelerate seat wear.
Questions for the supplier
Leakage class and test standard, whether reverse pressure is allowed and at what tightness, seat and seal ring materials, fire-safe design, maximum temperature and operating torque for actuator sizing. Ask for the passport and test certificate.
Checklist
- medium, pressure, temperature
- pressure direction
- leakage class
- seat and ring materials
- fire-safe design
- actuator and torque