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"Food Grade" propylene glycol? - Page 4

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Posted by DJ on September 28, 2005, 5:20 pm

Brian Graham wrote:

Glycerin, I think, not glycol. Used for making soap and lubricants. But
yep, that's the goal of biodiesel makers, to find a buyer for the
purified glycerin, to also pay into the production process.


Posted by Steve Spence on September 28, 2005, 9:31 pm
Brian Graham wrote:

The inventor isn't recanting, he never claimed the cat part at all. That
was made up by the reporter to "enhance" the story.

Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net

Posted by daestrom on September 23, 2005, 8:33 pm

A couple of things...

"Food Grade" doesn't contain any toxic chemicals (makes sense... duh).  The
automotive stuff still has some rust inhibitors and junk.  So if you get a
leak, well you get the idea.  Of course, a double-wall heat-exchanger set up
is designed to protect you from such leaks.  If you don't have a double-wall
version, then you probably really should be using 'food grade' to be really

As far as pressure goes, you want enough to keep the panels 'flooded'.  This
isn't too bad on a single story house, but if they are up on the roof of a
two story, you have to think about it.  Water needs about 15 psi for 34 ft
of height.  So something along the lines of 15 psi is pretty good.

Your pump needs a minimum suction pressure to work well.  The manufacturer
data should tell you that.  If it's located down at the 'bottom' side of the
loop, the pressure you use to keep the panels flooded can also serve to
maintain the pump suction.  Which is why most installations put the pump
down near the lowest point in the system.


Posted by Nolan Tucker on October 1, 2005, 11:23 pm
 This is very helpful.  Since it has started getting cooler at night (low
40s) the pressure has started fluctuating - down to 0 psi at night.  But
back to 40 psi during a sunny day.  I replaced the expansion tank last
March, so the bladder is good.  I've checked the pressure there - 40 psi.
THere may be air in the tank - I don't know how to purge it.  Could this be
causing the fluctuation?


Posted by daestrom on October 2, 2005, 12:29 am

Such a large range of fluctuation sounds like there is no real expansion
volume.  If the tank is 'full' during the day with 40 psi, then a small
amount of contraction at night will double/triple the air space, and drop
the pressure by the same factor.

Of course, you don't want the air volume too big either.

You want some way to figure out just how full the expansion tank is.  More
than two-thirds or so, and you'll get these sorts of pressure changes as the
coolant expands/contracts.  Just how big is your expansion tank anyway?  And
how many gallons is in the system total?


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