Diagnosing Pressure/Flow Issues

[Alphite]

Hi,

I'm trying to diagnose issues with an existing water distribution system, and am looking for general guidance on troubleshooting, or even specific advice.

There are two storage tanks connected via bottom valves. They both feed a 3" pipe, which then splits to two distribution pumps, one for a hot loop, one for a cold loop. Both loops are fed by APV W+55/35 pumps. The hot loop discharges to a 2" line, the cold loop to a 1.5" line. The hot loop returns to the storage tank, the cold loop returns right before the pump (pictures attached).

Both loops have some cavitation, but the cold loop is much worse. I also connected an ultrasonic flowmeter after the cold pump yesterday, and the flowrate would start at 15 psi, then jump to 230 psi. It would be stable at each rate, but cycle from one to the other every couple of minutes (the flowmeter appeared to be accurate). The pump discharge pressure seemed consistent (40 psi), and the vfd was a constant 50 hz.

My question is - what is the best way to accurately develop a model for this system, that explains the cavitation, flow and pressure issues, and what additional data do I need to collect?

Thanks

 

[georgeverghese]

"flowrate goes from 15psi to 230psi" - you mean 15gpm to 230gpm ?

Would guess gas has gotten into the cold loop user return line ( blue vertical line on lower sheet). What are these units using cold water, is there gas at one or more of these users at a higher pressure than supply cold water. Gas could leak into the return cold water. Show us the PFD for these users on the cold loop and state the pressures also.

By the way, why the forward sensing PCV on this cold return line?

 

[mk3223]

The P&ID doesn't indicate that the tanks have the vortex breaker on the water outlet. And, the gas may get into the the pump suction through these nozzles, and cause cavitation.

 

[Artisi]

OP & mk3223, What cavitation?
You need to fully understand the phenomenon of cavitation before assuming what is very unlikely to be a cavitation problem.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Well normally we have to ask for detailed information, but this goes into too much right at the start.

~Can you put together a more schematic description complete with relevant pressures and flow so that we ( or at least I) can try and understand what is going on.

you should try drawing this and see where you have missing data such as flow or pressure and then try and collect it.

To have any system where flow is somehow being separated from pressure implies some diversion of low into place you can't tell, but I just can't understand your system at present.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.