[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

CO2 regulators

Hello Dave Gomberg / David Ozenne,

I wasn't trying to show a design that would dump. Most if not all
Pressure Reducing Regulators will not dump. Most will have a vent
port in the spring chamber to vent the gas away should there be a
diaphragm failure (1/8" NPT in design drawing and SECTION II, 13
of CASHCO MODEL D IOM). Some regulators will release the excess
pressure through the outlet port (in the case of BHT 100,
BHS 280 & 281 from BOC Gases) therefore causing the outlet / 
downstream pressure to increase hence "not designed to protect
downstream apparatus". Other regulators will have a vent / vent
port (in the case of BHS 500 and BHS 270 from BOC Gases) to release
the excess pressure to the atmosphere through a small hole (vent) at
the side or back of the regulator or with a threaded port (vent port)
for remote discharge. Go to BOC Gases web site and take a look at the
typical applications of the respective models and you should be able to
figure out why.

The above "dumping" is in the case of diaphragm failure. If you are
talking of "dumping" as when the CO2 tank near empty, the dumping
is at a pressure lower than the SET pressure (governed by the
existing spring force setting prior to dumping).

Just to make things easier to understand, assuming that you have managed
to adjust your pressure reducing regulator for an outlet (working) pressure
of 20psi and the system is running normally (steadily). Assuming the diaphragm
has a 2 sq. in effective area. The force exerted by the spring would be
approx. 40 lb force. 20 psi (20 pounds per square inch) x 2 sq. in =40 lb.
If the outlet pressure is lower than 20psi (due to CO2 discharged through
diffuser or reactor), the force exerted by the diaphragm will be less than
the spring force so the valve will stay open for more gas from the inlet
port (high pressure side ) to pass through the valve seat to enter into
the outlet side of the regulator which is also the diaphragm chamber. As
more gas from high pressure enters into the diaphragm chamber, the pressure
will build up until the stage when the pressure in the diaphragm chamber
reaches slightly more than 20 psi, the force exerted by the diaphragm will
then be more than 40 lb which will overcome / counter the spring force and
closes the valve such that the flow of gas from the inlet port (high
pressure side) will stop completely (or almost) as such the pressure in
the outlet port will not go up any more. The only time the pressure
reducing regulator will dump or valve stays open other than diaphragm
failure is when the inlet pressure is lower than 20 psi then the force
exerted by the diaphragm will be lower than 40 lb so could not overcome
the spring force.

So, if higher than set presssure 20 psi can happen in the so called
"dumping" situation, the pressure regulator will not have been working
normally / steadily in the first place.

As to why inlet pressure decreases, the outlet pressure increases, I do
not have an explanation now and I do not doubt your observation. I have
sent email to a manufacturer of pressure regulators asking them to provide
explanation but did not get any reply from them till today. Maybe it has
got something to do with high flow rates, isothermals / Gas-laws etc..
If anyone can explain why or point me to a web site, I would be very happy
to hear from her / him either by posting to the list or to my email address.

If you are not using a Pressure Reducing Regulator but a Back Pressure /
Relief Regulator (see Cashco site) wrongly configured as a normal Pressure
Reducing Regulator or if you connect a Pressure Reducing Regulator the
other way round you MIGHT face funny problems. I leave it to you to figure
out since some of you people like to DIY without studying / understanding
the details.

If any of you like to have more explanation, you can email me direct and
make sure you don't complain that your email storage is full after that.

DUMP (other than diaphragm failure).

A pressure reducing regulator is for limiting (not regulating strictly
speaking) the max downstream pressure. A flow / needle valve is for
controlling / regulating the flow. IMHO a proper CO2 system should have
both a pressure reducing regulator and a flow vale for proper / steady /
no dumping CO2 dosing. You can make it work in some situations without
one of them, but then don't complain if you have problems later.

Casey Huang 

>Date: Thu, 28 Sep 2000 13:19:48 -0700
>From: Dave Gomberg <gomberg at wcf_com>
>Subject: Re: CO2 regulators
>At 03:48 PM 9/28/00 -0400, Casey Hwang wrote:
>>  http://www.cashco.com/download/diom.pdf
>Nice page Casey, but I fear that design won't dump.  If the high side 
>pressure decreases, the time the seat is open just increases a bit and the 
>same statics that applies at a higher input pressure still governs.   No, 
>this is the kind of regulator Neil was talking about, not the kind that
>- --
>Dave Gomberg, San Francisco            mailto:gomberg at wcf_com
>NEW Planted Aquaria Magazine:        http://www.wcf.com/pam
>- -----------------------------------------------------------------
>Date: Thu, 28 Sep 2000 17:33:44 -0700
>From: "David Ozenne" <dozenne at 10fold_com>
>Subject: Re: Pressure Regulator
>Casey thinks I'm wrong about how a pressure regulator works.  It is
certainly true that I've never studied the mechanical details.  But from an
experimental standpoint, I stand by my statement that as the inlet pressure
decreases, the outlet pressure increases.
>Perhaps I should clarify my statment about the regulator becoming an open
valve.  For a given setting of the adjustment screw, a lower inlet pressure
will result in a higher "set" point for the outlet pressure.  Eventually,
as the inlet pressure decreases, the set point will exceed the inlet
pressure.  At that point, the diaphragm stays open, and the regulator is an
open valve.
>Assuming that what you have downstream of the regulator is effectively a
flow restriction device (be it a sintered glass diffuser, needle valve,
etc.) the flow will increase with the square root of the outlet pressure.
This may be hazardous to your fishes' health.  Furthermore, if the hardware
that you have on the downstream side can't handle the additional pressure,
you could be in for even more trouble when, for example, the airline tubing
pops off of the nipple.  
>Of course, the other possibility is to have a second pressure regulator
downstream.  I've never dealt with a dual stage regulator personally, but
assuming that it is effectively two standard regulators in series,
decreasing the inlet pressure will increase the inlet pressure to the
second regulator, and actually *decrease* the final outlet pressure.
>David Ozenne
>Fremont, CA