According to Dow Chemical propylene glycol is completely soluble in all 
proportions in water. It “dissolved" into the water. A liquid dissolving into 
another is a notion we rarely think about. You ended up with about 90 gallons 
good for 15F. That is 25% glycol or 22.5 gallons glycol in a 90 gallon mixture. 
You had planned for 60 gallons mixed. That would be 22.5 gallons glycol in 60 
gallons total. That is about 37% glycol.  So you must have been shooting for 
about 0 F. In other words the premix was for about 0F in order for the numbers 
to make sense.

Allan Seidel
St. Louis, MO


> On Oct 20, 2015, at 9:59 PM, Douglas Hicks <[email protected]> wrote:
> 
> We installed an isolation valve on an propylene glycol antifreeze loop.  
> Unfortunately, we were told the system was about 55 gallons. It was closer to 
> 90 gallons.  We only had enough antifreeze for 60 gallons.  We used what 
> antifreeze we had, and finished the job with straight water.  My thought was 
> to drain the water, monitoring the liquid until we got to the antifreeze.  
> Then we would fill the system with an antifreeze mix.
> 
> Today, we returned  to the job site with  30 gallons of antifreeze.  We 
> closed the isolation valve and drained out 5 gallons.  The drained water 
> tested  to 15°F.  We tested the fluid at the other end of the piping.  It 
> also tested 15°F. I thought the antifreeze loop was a closed system.  How did 
> the antifreeze and water get mixed in a closed pipe system?  
> 
> Douglas Hicks
> General Fire Equipment Co of Eastern Oregon, Inc
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