Pneumatic signal

How to read it

A pneumatic signal is a variable air pressure sent through metal or plastic tubes, as Kuphaldt’s Lessons In Industrial Instrumentation describes it, and the commonest standard range is 3 to 15 PSI. The DOE’s handbook gives the same range for the pneumatic signal that comes out of a current-to-pneumatic (I/P) converter to drive a valve. Course notes by Peter Woolf and others call the line the pneumatic impulse, information sent by a gas.

Kuphaldt’s chart draws it as a thin line crossed at intervals by pairs of short slashes, and notes that since the 2009 edition of ISA 5.1 the same line can carry a continuous or an on/off signal.

Also searched as: pneumatic signal p&id symbol, pneumatic signal symbol.

Look-alikes

A dashed line is an electric signal, and a line with small x marks a capillary tube. In the DOE’s chart, a line with double slashes is an air line or a defined process line, piping that carries air, rather than a signal; the DOE’s handbook notes that auxiliary piping may carry compressed air. The legend sheet says which reading a diagram uses.