I have a steam flow DP transmitter that has output swinging. Steam valve is in

I have a steam flow DP transmitter that has output
swinging. Steam valve is in manual.I have good steam
pressure. The impulse lines have steam tracing on them. The
steam tracing has a hole in it that is blowing raw steam on
the high side impulse line only. Could this be causing the
swinging?

Question Posted / todd

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I have a steam flow DP transmitter that has output swinging. Steam valve is in manual.I have good s..

Answer / carl_ellis

Answer:
Yes, live steam on an impulse line could cause pressure swings.

Blowing live steam on an impulse line could conceivably heat
the condensate in the impulse tubing enough to boil it.
Even if it doesn't boil, a deadheaded impulse line with have
thermal syphon flow occuring as the hot spot condensate
rises and its place is taken by cooler condensate.

If boiling is occurring, then it could be intermittent
boiling with associated pressure pulses: as the steam
bubble(s) move away from the hot spot and cooler condensate
takes it place.

None of which should be happening in an impulse line.

The high side is 'seeing' these artifacts as forces on its
diaphragm which is creating pressure swings.

Carl Ellis
Measure First