Why UNIFLOW Isn't a Butterfly Valve?

UNIFLOW looks like a butterfly valve but isn’t — the double-eccentric rotary design behind its sealing life and bi-directional shutoff, explained.

At a glance, NBS UNIFLOW looks like a butterfly valve — a disc, a shaft, a wafer body. NBS is explicit about this on their own technical documentation: “UNIFLOW is not a Butterfly Valve. It is a Rotary Valve.” The distinction isn’t marketing language — it describes a fundamentally different sealing mechanism with real consequences for service life.

The Problem with Standard Butterfly Valve Sealing

A conventional butterfly valve seals by pressing a disc directly against a seat on a single axis. Every open-close cycle drags the disc across the seat surface during the final degrees of travel — abrading both disc and seat over time. This is why butterfly valves in high-cycle or high-differential-pressure service tend to develop leakage well before other components in a system reach the end of their service life.

Double Eccentricity — What It Actually Changes

UNIFLOW’s rotary design offsets the shaft on two axes simultaneously — a primary and a secondary eccentricity. The practical effect: as the disc approaches the closed position, it moves away from the seat surface rather than dragging across it, then presses into final contact only at the last moment of travel. This eliminates the seat abrasion that limits conventional butterfly valve life, and enables genuine bi-directional sealing — tight shutoff regardless of which direction the pressure differential is applied.

Compact and Light — Without the Sealing Trade-off

Because the sealing principle borrows from ball valve shutoff performance while keeping the compact, lightweight rotary body, UNIFLOW achieves sealing performance closer to a ball valve at a fraction of the weight and installed cost — without the space and actuation torque penalties that come with a full ball valve assembly at larger nominal sizes.

Where This Matters

Any application with frequent cycling, bi-directional flow, or tight installation space benefits from this construction — which is exactly why UNIFLOW is the base platform behind BM TECH’s PSA, VPSA, ASU, LNG/LPG and chemical tanker valve service lines.

BM TECH — NBS Europe supplies and services the full UNIFLOW range.