The short answer
A full-bore ball valve has a bore equal to the pipe internal diameter, so pressure loss is nearly zero and the line can be pigged; a reduced-bore valve has a bore one size smaller than the line, which makes it lighter, cheaper and easier to operate, but it introduces pressure loss and rules out pigging.
Design differences
- Full bore: the ball bore is about equal to the valve end bore (usually equal to the pipe ID). The ball is large, the body is large, weight and torque are higher and the price is higher.
- Reduced bore: the ball bore is about one size smaller (roughly 0.8–0.9 times the pipe ID); for the same nominal size the body is smaller and lighter, and cost and operating torque are lower.
Key comparison
- Bore diameter: full bore matches the line; reduced bore is one size smaller.
- Pressure loss: negligible in full bore (close to straight pipe); measurable in reduced bore.
- Pigging: possible in full bore; not possible in reduced bore.
- Passage of inspection tools: possible in full bore; not possible in reduced bore.
- Size/weight/cost: full bore large/high; reduced bore small/low.
- Operating torque: higher in full bore; lower in reduced bore.
Selection by application
- Full bore is mandatory: valve stations and pigging stations (launch/receive) on long-distance pipelines, sections that must be pigged or inspected with an ILI tool, and high-flow lines where pressure loss must be minimal. This is a typical API 6D pipeline ball valve requirement.
- Reduced bore is acceptable: general isolation duty, space-restricted locations, price-sensitive projects, and larger sizes where flow demand is moderate. Reduced-bore valves remain an economical choice in systems with spare bore capacity.
- Note: when full-bore and reduced-bore valves are mixed in one system, the reduced-bore valve becomes a throttling point; pressure drop and velocity must be checked against process requirements.
How to specify it in RFQs and drawings
- Full bore is usually marked Full Bore (FB) and reduced bore Reduced Bore (RB); in some systems the reduced-bore size is described as "one size down" (the line at that point is DN300 while the bore is taken as DN250).
- The RFQ should state all four: nominal size, bore requirement, end connection (flanged/butt weld/threaded), pressure class and product standard — missing any one can lead to a wrong model being quoted.
- If pigging requirements are unclear, state whether the line has launch/receive facilities or in-line inspection (ILI) needs — this directly determines whether full bore is required.
- At drawing review, check the ball bore against the valve end bore to avoid a "nominal full bore, actual reduced bore" discrepancy.
Common misconceptions
- Specifying only "ball valve DN300" without full bore or reduced bore — the price difference is significant, and discovering after delivery that the valve cannot be pigged leads directly to rejection.
- Assuming a reduced bore is "cheaper at no cost": in high-velocity solids-laden service, the locally higher velocity at the reduced bore accelerates erosion and cavitation.
- Ignoring end connections: large-diameter full-bore valves are usually flanged or butt weld, while small reduced-bore valves are often threaded or socket weld; end connection and bore must be confirmed together.
Vexval's ball valve range covers full bore and reduced bore, floating and trunnion-mounted designs, and trunnion and fully welded construction for high-pressure large-diameter service, allowing selection by pigging and pressure-loss requirements.