Flow Fluctuating

what is fluctuating.. pressure and/or flow? more details are required, what is your pipe layout? lengths of runs, are there valves at teh end of the runs...

Before shutdown (TAM) it was ok but after that start fluctuating

no design issue behind this problem.

fluctuating only in flow not pressure of pump discharge

Are there any high points on the lines that fluctuate?

yeah pipes is moving up and down until reaching the extruder but the transmitter fluctuating is before extruder chute. maybe 20m from pump to extruder

I might be on the wrong train here, but it sounds as if you have a pipe with liquid that occasionally gets purged with gas. Flow/pressure fluctuations would likely be caused by inadequate removal/venting of the nitrogen when you start flowing liquid again.

Trapped gas, turbulence etc. It's not going to be an electrical problem though, I would post this in the mechanical engineering forum if I were you.

Actually not true, in fact I would think it is most likely electrical. We sent a batch of 600 commercial heaters to Japan, they rang and complained when they tested the items that the resistance reading were all out, having done the final test myself on the items I knew they were perfect when they left.

It took me a few days, then i asked them what season it was, when they said winter i asked where the items were stored, they said outside in the warehouse where they were used. i told them to take one into the office building, wait half an hour and test it again. the reading was normal.

Copper wire shrinks in extreme cold and alters the resistance level, thus restricting the flow of energy, the trace wire will be copper without doubt, and what is the substance in the lines? yep the coldest liquid on the planet

You cab bet without doubt the flow drop occurs within the 12 hours of the lines being filled, the following 12 hours will be when the trace wire has had time to not simply heat the pipes but remove the effect that is being applied to itself.

The chance of it being mechanical are very low, any leak even internally to another line or pump component trapping any liquid or gas would be noticeable a mile away, the outside would be frozen

we already flushed the line several times

If it is a trapped gas issue, which I still suspect, flushing the line will do little. The thumb rules I was taught for liquid piping systems is to maintain flow velocities less than 7 ft/s; for water systems this velocity does not provide the energy to purge the line of air. The pipes need to be vented.

Is there any difference in the lines?

Always the same 2 lines?

Do you use more than one supplier?

What was done before and after it started to fluctuate?

every two line are similar

the fluctuating is happend to 2 similar lines

we have one supplier only

What was done before and after it started to fluctuate?

upgrade DCS control panal software only (no cables)

the discharge pressure of the pump is stable

the temperature of the weston (liquid) is stable

the flow transmitter is fluctuating 12 hr then return normal.

the set up is a tank with nitrogen to make pressure of 1 atmosphere

pump that supplies 6 lines to 6 extruders

4 of them ok the other 2 are fluctuating

this is immediately after TAM ( turn around)

i don't know if electrical breakers or something with timer affects the reading, i don't understand electrical stuff so i hope from electrical point of view i may find a clue. the one with copper is actually good approach i may need more to look at

what affects instrument reading?

as you have posted this in the "Electrical" section, then you must suspect an electrical problem, so does the running current of your motor alter?

Have you checked the frequency of the supply? Have you checked the stability of the supply voltage? Any frequency variation will affect pumps/motors, control circuits, PLC and anything else

Is your motor tripping on any one of the following.. under or over volts... under or over Hz... under or over current.... current unbalance?

This would be a good place to start.

What is "Weston"? I guess it has to be liquid, so trace heating is important

Have you checked the tracing heating? Maybe the medium you are pumping is affected by temp changes, and the trace heating is not keeping it liquid throughout the whole length of the pipwork, therefore... (and just an idea), you may have it starting to solidify in the lines.

with that said, what type of pump(s) are you using? If the discharge pressure drops then the running current will drop, and if you have an underload trip, then your motor will stop.

The 12 hours of fluctuation what is the ambient temp and what time of day?

Just to close.. in a desert location in the summer my installed pumps designed to run at 60Hz were not producing as well as they did months earlier. It was then decided to pull these pumps and test them on a test bench, we found no problem, no wear everything as new.

When we looked further afield, we found the generator frequency was routinely reduced from 60Hz to 50Hz to save money on fuel as in the summer months to many A/C unit were on.

Hi Fahad.s

What procedure do you follow during TAM?

What is the difference between the culprits and the other line?

What is the possibility that an incorrect make or model sensor is installed on the 2 lines?

You could be experiencing 2 different issues that when the unite they can cause problems.

First if the distance of the piping from the pump to the receiving units is not uniform you could find that flow is following the path of least resistance and that would be to where the lowest pressure is.

Second the intermixing of the nitrogen since it may not be homogenized could be creating gas bubbles that as the difference in pressure due to the line differences can cause pressure drops where the gas forms pockets and could cause the fluctuations.

Unequal resistance of flow of piping. The flow always go the easiest path. Calculate resistance of each path and put properly designed orifice so resistance of each path is more or less equal to each other. This problem is known in water heated tall buildings.