Re: FROG and DIY CO2 Problems
>From: Tyson Lee <tyson at phoenix_net>
>Date: Fri, 26 Jan 1996 00:11:42 -0600
>Subject: Re: FROG and DIY CO2 Problems
>>From: gomberg at wcf_com (Dave Gomberg)
>>I talked to the FROG people and even got a data sheet. The FROG is NOT A
>>PRESSURE REGULATOR, it is a FLOW REGULATOR (that is what the FR stands for).
>>It is good in an application where it is the only component (other than the
>>tank shutoff valve) and is used to deliver its rated value (8CFH as I
>>It is not good where a regulator is needed because if you put something after
>>it intended to further reduce the flow, the pressure will just build up.
>>Basically, a FROG is a pinhole, which thereby reduces the flow. If you need
>>regulator, you need a regulator, not a FROG. Dave
>>Dave Gomberg, Experimenta San Francisco CA USA gomberg at wcf_com
>It simply seems to me that the pressure and flow are highly correlated. The
>package that the FROG came with states it is preset at 22SCFH. Hence, the
>regulator will try to keep the flow constant. Even if my needle valve
>causes back pressure, it would build up and increase the bubble rate from
>what it was previously set at.
This is 100% wrong. The FROG and a needle valve are trying to do the same
thing. A *pressure* regulator has an *automatically adjusted* valve that
controls the output pressure to a very constant value. There is absolutely no
correlation between pressure and flow rate until you have a device to make one
constant. If you set the needle valve to get a lower flow rate than the FROG
setting, the FROG just builds pressure on the needle valve back to increase the
flow rate until the FROG flow rate is satisfied. You could easily blow up the
needle valve with such a connection, so look out for shrapnel when you touch
it, if it has full tank pressure on it (below FROG bubble rate).
>Anyhow, what I am trying to say at this late hour is that the FROG _should_
>work for this application. I think George hit the nail on the head with the
>temperature sensitivity of the particular valve I have.
>Hell, maybe it is a combination of both the regulator not being a regulator,
>and the temperature.(I think I need sleep)
One way it could work safely is if you just used the needle valve to vent the
excess CO2 to the air, and wasted it. It would still be super unreliable and no
steady bubble rate would ever be achieved. The other safe way would be to buy a
FROG that had the right rating to give the bubble rate you want, and then put a
pressure regulator in front of it (between FROG and tank) to keep that rate
constant. The FROG is only a constant flow device at very high pressure drop,
or with very constant lower pressure.
>When I looked into it further, by fiance' informed me that the heat in her
>house died the same night a front came in. Soooo....that could very well be
>why the bubble rate is fluctuating so much. I will keep the list posted as
>I believe this setup is by far one of the most economical manual setups.
But it could kill you, if you don't understand the physics involved. Please,
please don't try to make it work, Tyson. It's not economical if you lose a
Wright Huntley (408) 248-5905 Santa Clara, CA USA huntley at ix_netcom.com