Re: good technical kegging reference

On 22 Jun 2006 10:23:11 -0700, <naramsey@xxxxxxxxx> wrote:
This raises another question. I have noticed the following behavior
that I don't fully understand.
Suppose I close the (output) valve on the regulator and open the co2
tank. The gauge reads some pressure. If I then hook up some closed
system to the valvue (e.g. an empty keg, or just the line with a
disconnect on the end) and then open the valve, the pressure drops and
stabilizes at some lower level. I would have expected it to drop
momentarily while the gas was flowing and then to restabilize at the
original PSI. Why is this?

Because consumer grade regulators are not very accurate. ;)

When you close the output side and open the tank you're hitting it with
a very quick burst and then the diaphram/spring is snapped shut. When you
connect the keg to it the diaphram/spring opens again and eventually closes
more slowly as pressure gradually equalizes. The diaphram/spring doesn't
shut at the same pressure both times. No, it's not really supposed to
do that, but it's a mechanical limitation in how they design these things
in order to make them relatively inexpensive.

Take a typical spring, stretch it fairly far and then suddenly let go and it
will spring back to one size. Take the same spring, stretch it open the
same amount, but this time keep your hands on the ends and gradually ease
off on how hard you're pulling the ends apart. Eventually the spring will
stop closing, but probably not to the same size as it did when you just
let go of it.

It would probably be more accurate to set the regulator screw with the keg
connected than it would with the output of the regulator closed. But it's
still not going to be 100% perfect. Also, over time these regulators can
drift in their ability to set a pressure. I haven't noticed it with mine,
but I've heard of some that after a couple of years don't register nearly as
accurately as they used to. IE, the gauge may say 10 PSI, but you've
really got 15 PSI coming through. It's probably due to the springs and/or
diaphrams getting worn out over time.

On a related note, regarging "dialing in pressure" for force
carbonation, I have heard people say that one should set the pressure
by closing the valve and opening the co2 tank to take a pressure
reading, and then adjusting the pin and repeating until you get the
right pressure reading. Apropos my question above, this is not the
pressure that will in fact be delivered to the keg when the valve is
opened because the pressure will drop when you do this. Which pressure
do you pay attention to when you are reading the PSI from some table
for force carbonation?

As I mentioned above, the pressure on the gauge while the keg is connected
will probably be more accurate than the reading it shows when you close
the regulator valve and hit it with a quick burst of pressure from the
tank.. Also, keep in mind that when you first connect a new keg, gas will
continue slowly seeping into the keg over time as the beer absorbs CO2. The
gauge is only going to give you a meaningful reading when no gas is flowing.

IMO, you can close the regulator output valve and open the CO2 tank
to get your initial setting and then connect the keg (making the pressure
drop) until gas stops flowing. It may take awhile, but once the gas
stops and everything stabilizes, then you can "dial in" the pressure if
you want to fine tune it.

In a perfect world you wouldn't have to do that, but it should get you
close enough that it doesn't matter.

Also, you really should have a check valve between your keg and
the regulator. Some regulators come with a check valve built into the
output valve, but if yours doesn't you'll want to get one seperately and
put it inline. This prevents pressure from backing up the system into
your regulator. You'll be glad you did this the first time you over
carbonate a keg and the check valve prevents the keg from shooting beer
backwards through your gas line (which can ruin the regulator).


John.
.

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