# Re: Needle valves and nutrients

```At 03:48 AM 12/12/00 -0500, Jonathan Peakall <jpeakall at mcn_org> said:
> > I do have a needle valve Tom, and it has never helped in an "end of
> > tank" situation. In fact, I had a near tragedy.

There has been a lot of pontificating on how to set up a high pressure
system using a needle valve as a pressure dropping device.   A lot of it is
wrong.  Let me 'splain:

If you have a device (such as an Eheim diffusor) that runs at 15psi (more
or less), and you encounter an unprotected dump at end of tank, the input
to the Eheim will rise from 15psi to maybe 150 and a huge dump will occur
thru the Eheim.

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 needle
valve which has been set to drop the pressure from say 40psi where your
regulator is set to 15psi needed by the Eheim, the input to the needle
valve will rise from 40psi to 200psi.  Obviously, this is a smaller
increase than without the needle valve.   The problem is we don't know what
the effect will be because the flow will change from laminar to turbulent
throughout the system.  How this will affect the resistance of the valve or
the Eheim is not known.  I do know that the Eheim is very non-linear, and a
small boost in pressure makes a large boost in bubbles.  Raising the
pressure 10% from 15psi to 16.5psi can double the output.  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.

--
Dave Gomberg, San Francisco            mailto:gomberg at wcf_com
NEW Planted Aquaria Magazine:        http://www.wcf.com/pam
-----------------------------------------------------------------

```