Butterfly Valve function is similar to sluice valves and would be used in similar situations but would not be used in sewage installations. This valve is resilient seated and hence gives droptight closure over long periods.

The disc moves through 90 degrees and since shafts operate in self lubricating bearings the valve can also be used for less onerous flow regulations duties.

It is normal practice to size the valves such that the velocity is less than 5 m/s when velocities are larger it is necessary to take particular design precautions with regard to shafts, pins, gearboxes etc. These valves are very compact hence civil costs are minimised.