A Rotary valve is, a valve that controls by a rotary motion.
A rotary valve consists of–
- A body
- A Disk,/ plug/ ball
- A shaft and seal
- A seal ring
- Bearings for the shaft.
Rotary valves may be split up into
- Butterfly Valves
- Ball Valves
- Eccentric Plug Valve
Butterfly Valves are used for throttling, and on/off control, and are also compact and space saving, another good feature of their design is that they have a high recovery or a low pressure drop across the valve, much better than that of a sliding valve type.
1.Have the least body material making it cheaper, and lighter.
2.Can be lined for corrosion protection (example sea water lines)
3.Can handle higher flow than equivalent sliding stem type.
4.Compact so minimum space required.
6.Available in very large sizes (used in power station water inlet systems and as throttle valves Hydroelectric stations.
- High torque requirement (needs a lot of force to turn disc.)
- No noise or anti-Cavitation option. Small pressure drop
- Controls best only between 30 and 70 deg rotation
2.1 Further Types
The conventional disc is shown in the illustration, it has high dynamic torque, it is bi-directional and, cheap but it tends to rub on the seating material, which is not good as it could require a lot of maintenance.
It has an approximate equal percentage flow pattern
.2.1.2 Fishtail Disc
The fishtail disc has a lower dynamic torque than the conventional disc, and is only designed for one-way flow, but as the conventional disc, it also rubs the seating material and is expensive to manufacture.
2.1.3 Eccentric Disc
The eccentric disc has medium dynamic torque, also possesses linear flow characteristics. Because the disc prescribes, an eccentric path on opening it moves away from the seat and therefore does not rub the seating material, which increases the life of the seat seals.
Cost is between the other two.