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Re: My last (final) word on needle valves

> Date: Sat, 20 Jan 2001 07:30:56 -0800
> From: Dave Gomberg <gomberg at wcf_com>
> Subject: Re: My last word on needle valves
> At 03:48 PM 1/19/01 -0500, Chuck Gadd asks:
> >Or was Dave running the
> >regulator output at a higher pressure with the needle-valve?
> Yes, I was running my regulator flat out into the needle valve.  Unless 
> there is quite a pressure drop across the valve, the flow will not go sonic 
> and the valve will not restrict the flow as desired.

I assume Dave meant supersonic, which is the hard, final limit in most
valves, beyond which essentially no additional flow is even possible (aka
the "choke" point). You don't really need that, I think, as any highly
turbulent flow becomes quite non-linear and gives pretty decent flow
regulation. Most valves seem to regulate well enough with only a few psi
across them. I think that's why folks here now refer to them as "low
pressure" systems, as opposed to the Eheim with spring-loaded check valve
that takes 12-15psi just to open it.

I'd bet Dave's experiment did not remove that additional source of (useless)
back pressure, either. I know I left *mine* in while fiddling with various
valves, so I was working up around 20psi and above, while the actual drop
across the needle valve was probably as low as 5 psi. [It's just too much
trouble to get rid of the check valve in a nicely-working setup.]

The blue-green silicone tubing proved too soft to use on bayonet fittings at
much above 10-15 psi. At that level, a twist-tie, as used for plastic bags,
can usually keep it on. At 20-30 psi, I needed more drastic clamping, and I
still don't trust it very much not to blow out. It can balloon ominously at
much above that level. 

I suggest using regular vinyl airline tubing between regulator and needle
valve, with a good wire tie on each end. Otherwise, use polyethylene tubing
for that stretch, with Imperial-Eastman tubing fittings o/e. Some "plastic"
tubing is a good idea to protect the fish against catastrophic regulator
failure. I do not like attaching the valve to the regulator with only metal
tubing unless the needle valve is rated for 1000 psi or above (many are

Now *my* last word on this subject:

I really like the Eheim glass diffuser, even if it may need a "Chlorox" soak
once in a great while. 

I like the flow-regulation provided by a needle valve, but will remove the
Eheim check valve, in the future, so my low-pressure system is really
running at just the pressure drop across the valve. The end-of-tank rise of
a few psi will increase flow a bit, but not nearly as drastically as through
a fully-open check valve.

The sintered glass emitter provides a nice flow of very fine bubbles. If a
few reach the surface, they just increase CO2 concentration there, so little
is probably lost. [My tanks are well covered to keep my killies from trying
to move up the evolutionary ladder.] I also like Tom Barr's safe burping
system, but it is more obtrusive in my smaller tanks, so I'll wait a while
before getting any. The Eheim is so tiny it is hard to find unless the light
catches the bubble stream. That's a huge plus if appearance means anything.

In summary, I'll be using Dave's regulator and Eheim diffuser (sans check
valve), with Anthony's recycled fire-extinguisher tanks, and some kind of
in-hose needle valve to set the bubble rate with 10 psi or so of regulator
output pressure (high enough for proper regulation, anyway). Does anyone see
any fundamental flaw in this plan?

My mind is made up, so please don't confuse me with any additional facts.


Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

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