Quantity of water need to change static pressure

[Takket3]

i have a closed chilled water loop w/ glycol. total system volume is about 20,000 gallons.

I need to drain a section of pipe that is, fortunately, at the top of the system. This piece of pipe holds about 200 gallons of fluids.

I need to drain the fluid to totes to hold it while the pipe is repaired. One tote will hold the 250 gallons.

However... there is an certain amount of fluid that needs to be taken out of the system to release the system pressure, so there is more fluid I need to capture than just the 200 gallons. i know water is ALMOST incompressible, but not completely.

Does anyone know how to calculate how many gallons of fluid need to be taken out of a system just to release the static pressure? I can tell you that the pressure in the piece of pipe i'm draining is about 60PSI.

 

[RVAmeche]

One you start releasing fluid the pressure will drop very quickly; this is how thermal relief system works. I'm assuming the pumps and equipment will be off. Since this is at the top of the system, there will be minimal static head.

 

[Rputvin]

I looked up the sizing on an HVAC expansion tank sizer. 20,000 system gallons of 20% PG, 0.1°F temperature change (it wouldn't let me do 0), from 0 psig to 60psig is a volume change of 21.7 gallons. That jumps to 36.6 if you go up to 50% PG. Ethylene is 24.9 at 20% to 32.4 at 50%.

This is the one I have bookmarked, there are several others online.

https://westank.com/calculator/

I think your 250 gallon tote will be sufficient

 

[LittleInch]

Your missing bit of data is the volume of your pressurisation tank.

Any closed system will have an expansion / pressuriation tank. The volume of that could be several times that of the "pure" liquid expansion.

If you want a calculation look in the FAQs of this forum.

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

 

[LittleInch]

Basically you want bulk modulus of water

https://www.engineeringtoolbox.com/bulk-modulus-elasticity-d_585.html

Now the pipe expands a bit as well so probably double it and you won't be far off.

But dwarfed by the expansion vessel volume.

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

 

[Rputvin]

LI is right - the expansion tank for a 20,000 gallon system should be on the order of 500 gallons, depending on what conditions, ΔT/ΔP, it's sized for.

I put isolation valves on the expansion tanks of newer system to help prevent issues like this. Yours may have one, which would remove it from concern if it can be locked shut and tagged out.

Depending on the style of tank, if you don't have an isolation valve, may not have acceptance volume that matches the tank nameplate. The ASME code tanks are stamped with full volume, but the actual acceptance is below that for a bladder or diaphragm type.

 

[Takket3]

Thank you all for the replies! I will indeed isolate the expansion tank.