[John W]

Some instrumentation runs on air and those lines are prone to issues if not kept dry.

[ProtectOurFreedom]

Exactly right. Instruments and actuators run on 3-15 psi air with 3 psi corresponding to 0% and 15 psi corresponding to 100%. The control logic running power plants up until 30 years ago was all pneumatic, but that has greatly reduced as digital controls took over. The same air powers actuators that move valves, fan dampers and lots of other devices.

Water comes into the "instrument air" via the humidity in the ambient air and it can condense into liquid water when the air expands in the system. Therefore instrumentation air must be kept perfectly dry. This has been well-known in industry for many decades. There are dryer systems on all instrument air systems.

In the old pre-digital days, 3-15 psi pneumatic logic controlled everything in power plants. These were large analog computer systems running on air performing all the calculations needed to run all the subsystems in a power plant.

It is astonishing to me that instrument air is a problem today.

Here is a simple schematic of the basic flapper that provides back pressure on the nozzle.

See "Instrument Air Quality" for more info.