reducedbore

Reduced bore, written as reducedbore in some technical texts, refers to a section of a piping or flow system where the inside diameter decreases from a larger upstream size to a smaller downstream size. This can occur with fittings, valves, or sleeves designed to connect pipes of different nominal sizes. Reduced bore fittings are usually categorized as reducers, which come in concentric (centerlines aligned) and eccentric (centerlines offset) varieties.

In practice, a reduced bore affects fluid flow through changes in area, velocity, and pressure. By continuity, the same volumetric flow rate must pass through the smaller cross-section, causing an increase in fluid velocity and a drop in static pressure downstream, as described by Bernoulli’s principle. The magnitude of the associated minor losses depends on whether the reduction is abrupt or gradual. Abrupt contractions tend to generate higher energy losses and potential flow separation, while gradual or conical reducers are used to minimize such losses and improve flow uniformity.

Design considerations for reduced bore sections include the size ratio between upstream and downstream diameters, the fluid’s properties (density, viscosity, compressibility), flow regime (laminar or turbulent), and operating pressures. In compressible fluid applications, additional attention to pressure waves and potential surge is needed. Material compatibility, installation geometry, and alignment (for concentric versus eccentric reducers) are also important to avoid issues such as misalignment, vibration, or entrained air.

Reduced bore components are common in water supply, oil and gas piping, chemical processing, and HVAC systems, where changing pipe sizes helps adapt to different equipment or service requirements.