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Needle Valves and Nutrients

Dave wrote:  " So some experimentation in this area is required if you wish
to trust your system to a needle valve. If you have a device (such as an
Eheim diffusor) that runs at 15psi (more or less), and you encounter a dump
at end of tank protected by a secondary regulator which has been set to drop
the pressure from say 40psi where your primary regulator is set to 15psi
needed by the Eheim, the input to the secondary will rise from 40psi to
200psi. The problem is we don't know what the effect will be because the
secondary regulator may or may not tolerate 200psi. If it is a natural gas
regulator it may break down. Then it may be worse that with no protection at
all. You must carefully quiz the maker of your secondary regulator to ensure
that the 200psi won't be a problem. I hope this helps clarify just how
complex this issue is. And I hope it saves the fish of someone relying on an
untested needle valve setup. BTW, you can borrow a high output pressure
regulator (one that can go to 400psi for example) and simulate a dump and
test your system's performance under those circumstances. Be sure to take
all necessary safety precautions if you do this tho. "

This is just wrong for Dave's system and for the rest of us that use CO2
service (Beer tap) regulators.  For "Draught beer dispensing equipment and
related components"  pressure relief devices (relief valve) are required on
the outlet side of the regulator.   Dave uses Cornelius Beer Tap CO2
regulators.  They come equipped with a pressure relief valve that "protects
against overpressure" (Rapids Catalog).  Since I use Norgren regulators I
got their spec sheets.  The Norgren regulator has a pressure relief valve
that "will limit the outlet pressure to 70 psi maximum."

So.  With an end-of-tank dump, or even with a catastrophic failure, the
maximum outlet pressure is limited to 70 psi, not 400 psi or even 200 psi.
This is well within the range of almost ANY needle valve or secondary
regulator. 

My end-of-tank dump was on a commercial system (Sandpoint) that used a
metering valve to control the regulator outlet pressure.  It took a while
for me to understand what happened.  My solution was a second regulator AND
needle valves which even I consider overkill.  However if you have a good
needle valve and use the beer regulator factory set pressure (around 50
psi), the maximum pressure you will ever see at the needle valve will be 70
psi.  That difference will cause an increase in flow but not so much as to
crash a system in the short run. 

This is, in my view, a case against high pressure systems (diffusers).  If
the flow is predicated on a set pressure, the effect of a higher pressure
can cause a much higher volume of CO2 to enter the tank.  For low pressure
systems the increase flow is effectively linear (for illustration purposes)
at these pressures, e.g. 50 psi to 70 psi = 20 psi increase will increase
flow by about 40 percent.

Let the flames begin!

Lyndle Schenck