The ball valve is a quarter-turn suitable for gas, compressed air, liquid and slurry service. The use of soft-seat materials such as nylon, delrin, synthetic rubbers and fluoridated polymers imparts excellent sealing ability.
With fluoridated polymer seats, ball valves can be used for service temperatures ranging from –450 Deg. To 500 Deg. F; with graphite seats, service temperatures as high as 100 Deg F are possible. Also, the metal backing seals, the valves can be used in fire safe services.
Ball valves are similar to plug valves in operation. They are non-biding and provide leakage tight closure. The valves exhibit negligible resistance to flow because of their smooth body and port.
Ball Valve consist of a body which houses a rotating ball which has bore machined directly through it. The ball is located in the body by two sealing rings.
Rotation of the ball through 90° opens and closes the valve and allows fluid to flow directly through the orifice. In the closed position, the blank sides of the ball block the inlet and the outlet preventing any flow.
Conventionally, the handle that is attached to the ball is in-line with the axis of the pipe when the valve is open; conversely, if it is at right angles to the pipe axis, this indicates that the valve is closed.
In order to insert the ball into the body, three different types of assembly exist. Not only does the type affect the ease of assembly, but it also influences the maintainability of the valve.
Two and three piece valves – The body of the valve is split in one or two places in the same plane as the valve flange, and these pieces are bolted together. This has the advantage of simplified, in-line maintenance.
Top entry valves – The ball is inserted through a bonnet in the top of the valve. This facilitates in-line maintenance.
Single piece valves – The ball is enclosed in the body by an insert fitted along the valve’s axis. This eliminates the possibility of body joint leakage and any chance of disconnection whilst in service, but when maintenance is required, the whole valve has to be removed from the pipeline.