In brief
A ball valve is a shut-off valve whose bored ball fully opens or tightly closes the flow with a quarter turn.
Contents
What is Ball valve?
The body houses a ball with a bore, supported between two seat rings. When the bore is aligned with the pipe, the medium flows almost unhindered; after a 90-degree turn, the passage is closed. Ball valves switch quickly, seal reliably and are widely used in water, compressed air, gas, oil and chemical lines.
A distinction is made between full-bore and reduced-bore ball valves, one-, two- or three-piece bodies, and two-way and multi-way valves with L- or T-port. In smaller nominal sizes, the ball is usually floating; in large sizes and at high pressures, it is trunnion-mounted. Key ratings are nominal size (DN), nominal pressure (PN), connection type such as thread, flange or weld ends, body material, seal material and temperature range. For actuators, a top flange geometry to ISO 5211 is common.
Ball valves are designed as shut-off valves, not control valves; partial opening damages the seats. Failures are caused by worn seals, deposits and leakage at the stem. For automated valves, valve and actuator should be considered together, as torque and connection geometry must match.
In practice: maintenance and procurement
For a replacement, DN, PN, connection type, face-to-face length, materials of body, ball and seals, medium and temperature are needed. For automated valves, the top flange, square drive and actuator data must also be stated.
Synonyms and abbreviations: ball cock · three-way ball valve · shut-off ball valve · quarter-turn valve
Frequently asked questions
What is the difference between a ball valve and a butterfly valve?
A ball valve shuts off with a bored ball and, when full-bore, offers almost no flow resistance and high tightness. A butterfly valve uses a rotating disc that remains in the flow even when open. Butterfly valves are lighter and less expensive in large nominal sizes, while ball valves are preferred for small and medium nominal sizes and high tightness requirements.
Can a ball valve be used for control?
Standard ball valves are built for the open and closed positions. In intermediate positions, the medium flows past the seat edges at high velocity and damages them. For control tasks, there are special control ball valves with a V-shaped ball opening or segmented ball. Otherwise, control valves are the appropriate choice.
What information is needed to replace a ball valve?
The nominal size, nominal pressure, connection type and thread or flange standard, face-to-face length, full or reduced bore, body and seal materials, medium, temperature and operation by lever or actuator are needed. For automated ball valves, the top flange, square drive size, torque and actuator type are added.
What do full bore and reduced bore mean?
With full bore, the ball bore corresponds to the inside diameter of the pipe; flow resistance and pressure loss are minimal, and the line can, for example, be pigged. With reduced bore, the bore is smaller. This makes the valve more compact and less expensive, but it causes a higher pressure loss.