impulse tubing

Hi ronron,

Sloped down from what and to what?

(more info would help a lot)

Mike

For achieving better accuracy & perfomance. That's why we maintaining slopdown for gas or liquid service

It is not only sloping down, we prefer them on the lower side of the pipeline too (approx at 90 deg position) to aviid the air bubbles from entering the tube and disturbing my readings if that is what you mean. But then again at the end (if it the impulse tubing terminates at a cabinate) it goes up and at the highest point we put a vent valve.

Guessing If this is what you mean.

I am assuming that by "lead" you are referring to the impulse tubing used with pressure and pressure differential transmitters (PDTs, LTs, FTs etc.).

The slope is required especially for gas or vapour services which are mounted above the tapping points in order to ensure that any condensate build-up (which is inevitable) will drain back into the pipe and not remain in the impulse lines and sensor housing and act on the sensor therefore creating inaccurate differential pressure readings.

API-RP-551 Section 2.3.2.2 states; "A positive slope, at least 1:12 for all leads, should be provided."

The slope is provided for better draining/venting of impulse lines and also to avoid any liquid/vapour pockets in the impulse lines which will affect the correctness of measurement.

R.Thiyagarajan

for liquids, the measuring device should be lower than the source.For gases, it should be higher,except for steam, which should be lower or have a pig-tail fitting to trap liquid.Basically, no liquid in a gas measuring line, no vapor in a liquid measuring line.Simple,eh?