Pressure build up in a pipe system containing solvent
Pressure build up in a pipe system containing solvent
(OP)
Ok, having a bit of trouble here. there seems to be a gremlin in a system at work that is causing a pressure build up but we cannot find the cause.
in essence, the system is run off a huge vertical storage vessel, the solvent is pumped out via a pump at approximately 40psig. This then feeds two dispensing guns, 4 large mixers, 5 washers and a dispensing room with three outlets. The pump is only activated when a dispensing point is operational, and stops as soon as operations cease. The issue at hand is that there is a large pressure build up, intermittently, of up 150psig. Enough so that it can blow through a dispensing guns trigger operation.
Im looking for any help or ideas at what could cause such a build up within this kind of system and to this magnitude. Any ideas are welcome and happy to explain further details if you need more information.
thanks
Sean
in essence, the system is run off a huge vertical storage vessel, the solvent is pumped out via a pump at approximately 40psig. This then feeds two dispensing guns, 4 large mixers, 5 washers and a dispensing room with three outlets. The pump is only activated when a dispensing point is operational, and stops as soon as operations cease. The issue at hand is that there is a large pressure build up, intermittently, of up 150psig. Enough so that it can blow through a dispensing guns trigger operation.
Im looking for any help or ideas at what could cause such a build up within this kind of system and to this magnitude. Any ideas are welcome and happy to explain further details if you need more information.
thanks
Sean





RE: Pressure build up in a pipe system containing solvent
What event/sensor or ?? causes the pump to run?
Are there flow check valves installed, and where are they.
I'm guessing it a positive displacement pump.
Are certain dispensing points more likely to cause the pressure build up?
Regardless, I'd be thinking about stuff like accumulators, pressure relief valves, and circuits to bleed/recirculate fluid from the pump discharge back to the main storage vessel.
6 down, 14 to go.
RE: Pressure build up in a pipe system containing solvent
If the main pressure isn't supposed to be that high, possibly something is allowing the compressor to run unattended, forcing the system pressure to rise.
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Pressure build up in a pipe system containing solvent
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RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
In regards to the tank, it is its self approximately 5 meters high and operates at atmospheric pressure. the exit to the tank is on the same level at the pump and all the dispensing points other than the 4 mixers which are at about 3 meters above ground.
The pump it automatically operated by sensors and switches, depending on the operation tool. Although this has already been tested and the pump shuts off immediately when operations cease.
I don't believe there are any flow check valves but would have to double check that one.
the pumps are centrifugal pumps that operate at approximately 3 bar and pump at a rate of 12000L/h.
I'll try to get any other information tomorrow (home time for me) and I appreciate the advice guys.
Current theory is possibly water hammer effect that gets "stuck" behind the only NTV which is directly after the pump but its a hard one to prove.
RE: Pressure build up in a pipe system containing solvent
If this issue only arrives when you've got one dispenser running then it might be surge, but only a few degrees C will make a massive difference in pressure.
It could be something like a stretch of pipe is exposed to sunlight at certain times of the day and not others.
You'll need to try and get as amuch as you can from the pople who see it and try and find out what is going on when these pressure spikes appear.
Are they fast rise, slow rise?
How often does it happen?
Can it be replicated?
Try and formulate a set of trials to work out if its surge or temperature.
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RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
I would also strongly recommend installing pressure relief valves throughout the system to prevent potential human injury.
RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
Again I know this isn't much to go on, but I'm new in this role and just looking for any spitball ideas that I can look at or test.
As always, I appreciate all your suggestions and advice.
RE: Pressure build up in a pipe system containing solvent
In order for just one line to develop high pressure, it suggests there is a check valve somewhere along each pipe, or at least THAT pipe.
If 100% positive prevention of back flow is not needed, a strategically place leak/bleed would prevent pressure build up.
19 down, just 1 to go.
RE: Pressure build up in a pipe system containing solvent
From what I can tell, which is why were having so much issue with it, is that there shouldn't be any way, other than the pumps, that pressure is input into the system. All the washers and stirrers aren't pressurized and the fluid is poured straight in, and all dispensing points are essentially open ended. All solenoids are run on a slow down procedure, which means when they detect that whatever they're filling is reaching the desired weight, they slowly close the valves. The pipe goes over the same bridge as several other pipes, so if there were thermal expansion in this pipe, it would also be in all the others. While there are no relief points, the centrifugal pumps should not be able to pump any more that 3 bar and about 3L/s. These have also been tested and they turn off as soon as all operational points cease using the fluid. The storage tanks are not pressurized either, so the max pressure at the bottom of the tanks when full is no more than 0.5 Bar.
At this point there is no silly suggestions, anything outside the box is welcome. Anything I can test or research is a positive step forward.
Thank you for all the suggestions so far, they have all be most appreciated
RE: Pressure build up in a pipe system containing solvent
Exposed pipe in the sun can hit 60-70C and you might find that your liquid is boiling, but all depends on what it's physical properties are.
What are those vertical tube like things just downstream of the pumps? and on the lines in the solvent dispensing area? Why is only one connected in a through flow system?
you are only showing one PI upstream of the non return valves. Where are you measuring this 150 psi?
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RE: Pressure build up in a pipe system containing solvent
As for the point at which the pressure is displayed, the Gauge is located at the dispensing gun in the production room. The Gauge hasnt been added to the drawing yet as it was only added fairly recently. But thank you for pointing that out, something I can do fairly quickly today.
RE: Pressure build up in a pipe system containing solvent
Only thing I can suggest more is for YOU to physically check the entire run of pipes from tank through to each dispensing point using your drawing just to make sure no one has added a tapping point or connected something to any of your blanked off valves. don't trust anyone else with this.
Also figure out how much of your pipework in volume is exposed to any form of solar heating. It might only be 20% of the entire volume, but could easily raise pressure by 7 bar if you get s ay a 20C rise in temperature. Solvents and hydrocarbons in general are notorious for thermal expansion / pressure rise issues.
Find out what it's volumetric temperature expansion co-efficient is. Some typicals for solvents are 0.0015 m3/m3/C. Water by example is 0.0002, so 8 times worse than water.
Try and get a history of these pressure rises to see when they occur and what was happening before and during it.
otherwise just fit a pressure relief line back to the tank or fit a pressure accumulator d/s the pumps NRV set at some suitable pressure which doesn't impact on the D/S equipment.
It could be your system is just new and the non return valves are seating better than any other system where there are few more leak paths.
Keep us informed.
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RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
At this point I have given up trying to find the cause because this system simply shouldn't physically be able to build up 20bar in 15 minutes then just stop. So I've moved onto designing a modification to the system to allow it to be used safely.
RE: Pressure build up in a pipe system containing solvent
Is the solvent stored somewhere that's much cooler than the rest of the factory?
A.
RE: Pressure build up in a pipe system containing solvent
Have a close look at the end of the dispenser - is it below liquid level? Can it get reacting fluid back flowing into the pipe??
Still better to solve this at source, but a pressure relief back to the tank would be a good idea in any case.
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RE: Pressure build up in a pipe system containing solvent
LittleInch, the dispensing pipe into the mixer is at the top of the vessel, and the feeding pipe even higher. There isn't any way that some other material could work its way back into the pipe by that route. Also it wouldn't explain why the pressure build up suddenly stops when the hand gun is used briefly.
RE: Pressure build up in a pipe system containing solvent
If you only suck in a small amount of material then it will only generate a certain amount of gas which is then relieved as soon as you operate the gun and then there is no more material to create any gas.
It's not easy to guess remotely, but it's all I can think off.
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RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
The real question on my mind now is; Why does the pressure build up so slowly after such an immediate event? After the water hammer, I recorded the pressure of the system every 5 minutes for 20 minutes:
0 minutes - 3 Bar
5 minutes - 8 Bar (+5)
10 minutes - 11.5 Bar (+3.5)
15 minutes - 14 Bar (+2.5)
20 minutes - 16.5 Bar (+2.5)
So what do you guys think could cause the pressure to build up so slowly over 20 minutes, rather that instantaneously?
RE: Pressure build up in a pipe system containing solvent
There's something else going on that you haven't figured out yet.
What happens if you leave a valve open somewhere? Obviously the pressure won't go up (which leads into the prior suggestions that you've got thermal build-up in a closed system), but how much comes out of that valve and over what time period?
RE: Pressure build up in a pipe system containing solvent
What happens to the pressure when the operations cease during plant closure?
RE: Pressure build up in a pipe system containing solvent
It still looks thermal related to me, but maybe there is somewhere a device which is taking out the high pressure then slowly pumping it back in?
I still think you're going to need to physically check the entire pipe run versus your P & ID / schematic to see if anything else is connected to this system that isn't on your drawing.
There is something weird going on here.
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RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
RE: Pressure build up in a pipe system containing solvent
3DDave, Its worth a try, but again the issue is that as soon as the pressure build up is relieved once through the dispenser, the pressure stops rising. A pressure increase from the sun, or some other constant thermal input, would resume after the pressure is relieved.
Furthermore we had another build up last week, completely different machine was used. Over the course of 100 minutes, it went up to 40 bar at a constant gain. When the valve was cracked open the pressure relief, from 40 bar down to 6, dispensed just over 7kg of solvent. Now (if we have a high estimate of 100m pipe with an average of 2 inch dia) that means there was a low approximation of 4% more fluid than there should be (closer to 5% with a slightly more accurate approximation). Which for a line that has an in-compressible fluid in it, is quite high. Furthermore the 40bar reading is simply the limit of the gauge that's on the line at the moment. When we relieved the pressure, in order to prevent damage to the gauge, it was still climbing at about 1 bar every 5 minutes.
I have a few more tests planned out for now, but this issue is just getting more and more peculiar by each passing week.
RE: Pressure build up in a pipe system containing solvent
The reason it might stop once you relieve it is that once the gas expands and forces some fluid out of the pipe then more gas production has a gas volume to expand into where the pressure rises much slower. Aslo if it is a small section where you're getting heat then maybe it's all evaporated.
I still think you need to run / view the entire line to see if you're getting hot spots (anything over 75C will make it boil) or some strange connection not on the piping diagram.
When you get to this condition, is it possible to start the pump and flush the line through a dispenser to see if any gas appears?
Anyway thanks for the update - too many threads just stop without any further information
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RE: Pressure build up in a pipe system containing solvent
Whenever the pressure builds up, we relieve it through the dispenser. As far as we can tell there is not gas getting out.
RE: Pressure build up in a pipe system containing solvent
So they did all the design work and went through all the budgeting and so forth and got a test item set up. All worked great with none of the draining, refilling, and bleeding they had to do before the self-sealers were used.
Then came the great news. Their test plane had ruptured a hydraulic line in the tail. Without a place to vent expanded fluid, the warmth of the sunshine was enough to exceed the ability of the lines to contain the fluid.
A short time after, when the hurt had worn off enough to talk about it, an old guy sitting nearby overheard the conversation. He said, "Yup, same thing happened 40 years ago when we tried it."
Which gives me an idea. Is the supply tank typically cooler than the rest of the factory? It may just be the cold fluid from the tank warming on the way into the distribution lines. I can imagine a bunch of interactions based on how much insulation there is, how much thermal mass there is, thermal conductivity, and time dependency. It may be that the solution is to warm the tank to close or slightly above the room temperature.
RE: Pressure build up in a pipe system containing solvent
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RE: Pressure build up in a pipe system containing solvent
The solvent is kept in external tanks, so if we say for argument that the temperature outside is 4C, the solvent line is about 60% outside with the tank, the other 40% is inside the factory which is kept at a cool 19C. I personally cant see 15C temperature difference making a 40 Bar increase. None the less, I will attempt to run some calculations to see what I can find.
RE: Pressure build up in a pipe system containing solvent
Depends on how you define reactive, but it does react:
see https://en.wikipedia.org/wiki/2-Butoxyethanol_acet...
and similar entry for 2-butoxyethanol.
Both will react with oxidizers, and air (containing oxygen) is one such; in the atmosphere, the reaction is catalyzed by pollution (sources of OH and similar radical species). Granted, it is likely to be a slow reaction if at room temperature, since the stuff will not burst into flame with contact with air. Might be worth a small scale lab test: half fill a tube with solvent (the other half being air), then cap it and measure any pressure rise.
Slow reaction in air (vapor phase presumably) yields formates of various types, and some aldehydes (propanal being one, which also has a fairly high vapor pressure), which should be identifiable by a decent lab chemist; if you have such on staff, give them a catch sample from the pressure relief and let them analyze it for those contaminants. From a quick look on google using "oxidation of butoxyethanol" as search term.
I do agree that the bp of this solvent is quite high, and it's unlikely that heat alone is creating a vapor bubble...but if some reaction creates lighter species, and more of them, from single molecules of solvent...well, you get my drift.
RE: Pressure build up in a pipe system containing solvent
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