A complete engineer's reference for specifying ball valves across oil & gas, water, cryogenic and slurry service.
A ball valve is a quarter-turn on/off valve that uses a rotating sphere with a bored center to start or stop flow. Turn the stem 90° and the bore aligns with the pipe (open); turn it back and the solid side blocks the line (closed). That simple mechanism gives fast actuation, a tight shutoff, and very low resistance when open — which is why ball valves are the default isolation valve across most process industries.
The key limitation to respect: a ball valve is an isolation device, not a control valve. Holding it partly open to regulate flow directs high-velocity flow across the soft seat, accelerating erosion and cavitation. For modulation, reach for a globe or control valve instead.
The single most important classification is how the ball is supported, because it sets the size and pressure ceiling.
| Attribute | Floating ball | Trunnion ball |
|---|---|---|
| Typical size limit | ~DN200 | DN200 and up |
| Pressure ceiling | Moderate | High / pipeline |
| Seat load source | Line pressure | Spring + line pressure |
| Relative cost | Lower | Higher |
"Full-bore" (full-port) means the ball bore equals the pipe inside diameter, so the valve adds almost no pressure drop and stays piggable for pipeline cleaning. "Reduced-bore" uses a smaller ball to cut cost and weight, at the price of restricted flow and a flow-step that blocks pigging.
Field note: for steam or any service with sustained thermal cycling above ~200°C, specify full-port rather than reduced-port. Thermal expansion in a reduced-port seat tends to increase seat-leakage risk over time — a judgment that comes from installed experience, not from a datasheet.
Body and trim selection drives both price and service limits. Carbon steel (WCB / 20# in Chinese grades) covers the bulk of general service; stainless (CF8 / 304, CF8M / 316, and Chinese 06Cr19Ni10 / 06Cr17Ni12Mo2) is specified for corrosive or hygienic duty. Seats are typically PTFE for tight bubble shutoff, or metal-to-metal (often hard-faced with Stellite) where slurries, coke, or high temperature would destroy a soft seat.
Full cross-designation tables and seal temperature limits are on the materials & flanges hub; for the Chinese-to-Western grade mapping specifically, see our Chinese valve material grades guide.
Procurement specs usually name one of these; confirm which governs before sourcing:
Note the regional pressure-rating trap: a Chinese PN flange and a US Class flange are not interchangeable by formula. The full standards matrix is on the valve standards overview, and the numbers are in our PN vs ASME Class guide and face-to-face dimensions guide.
Trunnion, full-bore, API 6D, metal or soft seat per isolation vs tight-shutoff need; fire-safe design where hydrocarbons are present (fire-safe and special service guide).
Floating, reduced or full bore, soft-seated, WRAS/potable where required; cost-driven material choice.
Extended bonnet, full-bore, cavity relief mandatory — see the cryogenic valve requirements.
Metal-seated ball valves with hard-facing survive far longer than soft seats, trading a perfect bubble shutoff for durability.
In a floating-ball valve the ball is suspended and pressed against the downstream seat by line pressure; this works well up to roughly DN200 and moderate pressure. In a trunnion-mounted valve the ball is anchored by upper and lower trunnions and the seats are spring-loaded into the ball, so it handles large diameters and high pressures where a floating ball's weight would overload the seat.
Choose full-bore (full-port) when you need unobstructed flow, minimal pressure drop, or piggability for pipeline cleaning. Choose reduced-bore for cost-sensitive, lower-flow, non-piggable services where the slightly smaller ball is acceptable.
Ball valves are quarter-turn on/off valves. Using them partly open for flow control erodes the soft seat and causes cavitation at the narrow gap. For modulation, use a globe or control valve instead.
Common references are API 6D (pipeline valves), API 608 (flanged/butt-weld steel ball valves), ISO 17292 (general-purpose steel ball valves), BS 5351 (legacy UK), and GB/T 12237 (China). Your project specification should state which one governs procurement and testing.
Yes. Where slurries, coke, or high temperature would destroy a soft PTFE seat, metal-to-metal seated ball valves (often with hard-facing such as Stellite) survive far longer, at the cost of a less tight bubble shutoff than soft seats.
Under GB/T 32808 the first unit 'Q' means ball valve, '4' a flanged connection, '1' a floating structure, 'F' a PTFE seat, '16' a PN16 rating, and 'C' a carbon-steel body (WCB/20#). See our Chinese valve model-number guide for the full seven-unit decoding.