Reduced Bore vs Full Bore Ball Valve: Cv, Flow and When It Matters

Quick Answer

A full bore ball valve has a ball bore equal to the pipeline inside diameter, so flow restriction is minimal and the flow coefficient Cv is close to that of the pipe. A reduced bore valve has a smaller ball bore (usually one nominal size down), which lowers Cv, increases pressure drop and is cheaper and lighter. Choose full bore when piggability, low pressure loss or accurate metering matter.

Bore Size and Flow Coefficient

The flow coefficient Cv is the US-gallon-per-minute flow at 1 psi pressure drop. A full bore valve approaches the Cv of the same-size pipe because the ball opening does not neck down. A reduced bore valve introduces a restriction, so its Cv is lower for the same nominal size.

Why Pressure Drop Matters

Every restriction costs energy and can change process control. In pump discharge, metering runs and compressor suction, the extra drop from a reduced bore may be unacceptable. Where the line is already sized with margin, the saving from a reduced bore is often worth it.

Piggability

Pigging pushes a cleaning or inspection pig through the line. A reduced bore creates a step the pig cannot pass, so pigged lines require full bore valves. This is common in pipelines, some hydrocarbon and sanitary services.

Cost and Weight

Reduced bore valves use less material and a smaller actuator in some designs, lowering cost and weight. For a large project with many on-off valves where pressure drop is not critical, the saving adds up. See the ball valve guide for sizing context.

Sizing Check

Use a Cv calculation to confirm the valve will not choke the line. Our Cv flow coefficient calculator shows how bore and Cv relate for a given service.