Abnormal pressures in fireline - out of box ideas?
Abnormal pressures in fireline - out of box ideas?
(OP)
I have been called to help troubleshoot some unusually high pressures in a fire line. The fire line experiences intermittent pressures (anectdotally from the client) on the order of 260 psi, which is about 70 psi higher than the storage tank at the top of the system. There is a PRV between the tank and fireline that should keep pressures at the fireline down around 125. If the PRV were to fail, we understand that pressures would rise to the HGL of the tank, which would be about 190 psi. How would pressures increase to a level higher than the tank though (sorry, I'm mixing my HGL and gauge pressure terms, hope it still makes sense)? The fire lines have a check valve in them so no water/pressure can back feed into the system. The fire protection company says the high pressure can be bled off of the fireline, which leads me to think that the high pressure is not (always) present in the distribution system. Has anyone seen a situation where a PRV intermittently works, and further that the surge pressure from such a failure gets locked into a closed system, like a fireline.
The residences also on the system supposedly all have regulators in their lines, and there isn't supposed to be any outside watering with culinary, so we haven't had any residential complaints of high pressures, ostensibly because all 300+ regulators are functioning properly and no one really is using culinary outside.
Any help? Pressures can't 'ratchet' up without outside help, so I'm stumped. I'll attach a little schematic for reference.
Thank you in advance for any ideas!
The residences also on the system supposedly all have regulators in their lines, and there isn't supposed to be any outside watering with culinary, so we haven't had any residential complaints of high pressures, ostensibly because all 300+ regulators are functioning properly and no one really is using culinary outside.
Any help? Pressures can't 'ratchet' up without outside help, so I'm stumped. I'll attach a little schematic for reference.
Thank you in advance for any ideas!





RE: Abnormal pressures in fireline - out of box ideas?
RE: Abnormal pressures in fireline - out of box ideas?
RE: Abnormal pressures in fireline - out of box ideas?
Might there be some you're not aware of ?
A recording pressure gage on the fire line might yield some clues. Can you try that ?
By the way what does "using culinary outside" mean ? Never heard of this.
good luck
RE: Abnormal pressures in fireline - out of box ideas?
A recording guage on the system has been in place for two days and has been steady at the normal 125#. 'Course there haven't been any high pressures in the fireline since the recording guage has been put on, either. There is not a recorder on the fireline, only a pressure warning system that notifies the fire protection company when the pressure's off-kilter and what it is.
Using culinary outside means using potable water from the 'city' (company or district) to sprinkle lawns or wash cars or drives, etc. The other option is to use the secondary (non-potable) water system to take care of the outside water use.
Thank you,
RE: Abnormal pressures in fireline - out of box ideas?
I had only heard of such a dual water system in Coalinga, CA before now. Still, there they call the non potable "blackwater" . Culinary water sounds like delicacy by comparison.
RE: Abnormal pressures in fireline - out of box ideas?
Is the pressure transient? A surge perhaps?
Is the instrumentation telling you the truth?
Is there a place where water can be trapped?
If the guages are telling it right, there has to be some added energy somewhere to supply the extra head. That can be a higher tank somewhere in the system, decelerating water, a pump somewhere. Something like that.
If what you've said is correct, there's additional energy coming from somewhere.
RE: Abnormal pressures in fireline - out of box ideas?
Several questions;
How long is the water main?
How long has the water main been in service?
Any grade changes in the water main?
Are there fire hydrants on the water main?
RE: Abnormal pressures in fireline - out of box ideas?
Is there a pump somewhere in the system that could be supplying additional pressure? [No]
Is the pressure transient? A surge perhaps? [This is my guess, I wanted to see if that reasoning made sense to others wiser and more experienced]
Is the instrumentation telling you the truth? [It has not been checked, but two blown expansion tanks on the fire loop system seem to verify the high pressures]
Is there a place where water can be trapped? [Yes, in the fireline...I'm guessing a surge occurs at times in the system as a whole, but it gets trapped in the fireline...does that sound like a valid explanation?...aside from a pump somewhere adding head, it's the only one I can think of]
bimr,
How long is the water main? [About 1 mile from the tank to the fireline, with the PRV at about the mid point]
How long has the water main been in service? [10 yrs]
Any grade changes in the water main? [Yes. One local low point and one local high point between the tank and PRV, one local low point between the PRV and fireline.]
Are there fire hydrants on the water main? [Yes, supposedly at 500' spacing ...at least that's how it was designed.]
Thank you all for your questions and responses.
RE: Abnormal pressures in fireline - out of box ideas?
Steve
RE: Abnormal pressures in fireline - out of box ideas?
RE: Abnormal pressures in fireline - out of box ideas?
www.tycovalves-na.com/ld/CROMC-0296-US.pdf
RE: Abnormal pressures in fireline - out of box ideas?
Steve
RE: Abnormal pressures in fireline - out of box ideas?
then even slight temperature rise with heat absorption from any source(s) can play havoc.
Such a situation's usual remedy is very small size TRV(thermal reief valve i.e very small sized PRV)
Thus a small volume is bled out to control system pressure within limits from the blocked-out pipeline segment.
Hope this clarifies/proves helpful.
Best Regards
Qalander(Chem)
RE: Abnormal pressures in fireline - out of box ideas?
Is the problem solved and a cause found?
Another solution only indirectly mentionen above as PRV is to install an pilot operated overflow valve : eg constant pressure valve constructed to keep the pressure at least at a certain level within the system and relief/portion out water if pressure exceeds set pressure.
If you set this a selected distance above working pressure, below pressure limit it will relief repeatedly when set pressure is exceeded.
Could be a better and more longtime solution for repeated overpressures at uncertain conditions and interval if it is impossible to pinpoint exact cause and volume.
RE: Abnormal pressures in fireline - out of box ideas?
RE: Abnormal pressures in fireline - out of box ideas?
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