Restriction orifice

ISO 10628-2 (groups 24-25, fittings and piping) / PIP PIC001 / ISA 5.1 (FO)

Drawn as

An orifice plate between two flange bars (a bar across the pipe with a gap in the middle), labelled "RO" or with an FO bubble.

Meaning

Fixed plate that limits flow: after blowdown valves, on minimum-flow lines and on purge connections. It is not a meter, so there are no dp taps. Becomes restriction-orifice.

Variants

Multi-stage ROs are drawn as several plates in series
Look-alike: orifice flow element (FE) has dp tap lines to a transmitter