convert BPS to SCFH - The Planted Tank Forum
 
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post #1 of 11 (permalink) Old 10-22-2014, 03:13 AM Thread Starter
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convert BPS to SCFH

I am having trouble with my co2 bubble counter and solenoid valve. When the solenoid gets hot the needle valve swells or something and the gas stops feeding. This renders the set up into a futile tailspin, no gas/solenoid stays on, solenoid stays on/no gas. I am wondering if a gas flow meter or some sort of fixed orfice would suffice in place of the needle valve. Is there a conversion factor for BPS to SCFH?

Please sahre any assistance or personal successes

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post #2 of 11 (permalink) Old 10-22-2014, 03:28 AM
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A bubble can be of any size so it can't be easily converted to SCFH unless you know the exact volume of the bubble. Just separate the Sol and NV so the heat doesn't affect the NV.
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post #3 of 11 (permalink) Old 10-22-2014, 06:31 AM
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What is "SCFH"?


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post #4 of 11 (permalink) Old 10-22-2014, 07:05 AM
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Quote:
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What is "SCFH"?
Standard cubic feet per hour, most likely.

That being said, I would imagine the amount of CO2 we are injecting per hour to be too low to be accurately resolved by a flow meter.

You can try separating the solenoid and the needle valve (run one inline) to determine if heat is indeed the problem, though this would be the first time I have seen this to be the case.

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post #5 of 11 (permalink) Old 10-22-2014, 12:45 PM
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Darkblade is correct in that the amounts we inject are very low. For example, with a reactor (low pressure injection), we inject CO2 in the range of about 10 ml/min (SCCM) on a small tank, and up to maybe 200 ml/min (SCCM) on a very big tank (like a 300 gallon tank). That's 0.021 SCFH to 0.424 SCFH. Very small amounts. Furthermore, the problem with measuring the flow rate is that the actual amount of gas flowing is dependent on line pressure (and to a lesser degree, temperature).

For instance, the line pressure for a reactor is under about 1.5 PSI, whereas a diffuser might be under 30 PSI. Using the ideal gas law, that difference in pressure means that at the same flow rate, the diffuser would be pumping out 20 times as much gas (because gas compresses). As such, "flow rates" measured with a diffuser would be far lower than that of a reactor since the gas is under higher pressure.

There are a ton of variables when it comes to metering and measuring how much gas we flow. I have all sorts of sensors and have played around with it quite a bit. The point is that you have no idea exactly how much gas you need to flow, and it's a moving target anyway.

Just resolve your solenoid/needle valve issue so it works correctly.


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post #6 of 11 (permalink) Old 10-22-2014, 08:02 PM
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This is only a guess based on what you see and tell us but I suspect there is a problem with what is cutting off the gas.
It is quite common for heat to make the solenoid stick rather than the heat making the needle valve swell. Common problem is that heat does cause the solenoid sliding part to stick either open or closed. But it can fool people because there is another small part and they can hear a "click" so they think it is working. But that is so common, I lean toward that being your real problem while the needle valve swelling is not one I read about.
This guess is assuming you have a solenoid that has a molded rectangle shape that is the common cheaper version sold?
Still guessing but I'm afraid what you will need to do is switch to a far better solenoid and then possibly to a better needle valve. Both do cost more!!! But otherwise what you may find is a world of heartache as a sticking solenoid can be weird. Heat up and stick so that it is either on or off, cool down and seem to work. But meanwhile driving you up the wall??
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post #7 of 11 (permalink) Old 10-23-2014, 02:14 AM Thread Starter
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Thank you for your replies and guidance.

I have a Milwaukee MA957 CO2 regulator/solenoid/needle valve and bubble counter. I use a pH controller to turn on/off the solenoid valve. I replaced the factory solenoid valve when its short life came to an end. The new solenoid valve is a high pressure stainless steel body unit. I have double checked it twice and am confident the it is operating properly.

Today I replaced the 0-140psi factory low pressure gauge with a 0-15psi one and found out the with the original gauge needle sitting on the zero peg the new gauge was pegged at the 15 psi mark. I have throttled down the pressure to 3psi with the solenoid valve open and after it shuts off it slowly creeps up to 8psi. Now the needle valve adjustment is no longer micrometer sensitive. I have moved the tank in front of the aquarium for now so I can easily monitor it operating.

Is 3psi a reasonable setting for the pressure to the needle valve/bubble counter?

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post #8 of 11 (permalink) Old 12-16-2014, 01:46 AM Thread Starter
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So, after tinkering around with the entry level set up that I had, I bought a high end dual-stage regulator, set the output to 0.5psig and adjusted the outlet needle valve that came with the unit and bam! It works beautifully. I eliminated the bubble counter and re used my high end solenoid valve.

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post #9 of 11 (permalink) Old 12-16-2014, 04:36 AM
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3 psi is too low for the output from the regulator. That regulator should be regulating the pressure to at least 10 psi, and 20 psi tends to work better. It is the needle valve that regulates the bubble rate, and at 10-20 psi, that needle valve will be very nearly closed, so a small movement will give a significant increase in bubble rate. If you use a smaller pressure the flow rate may be determined by the pressure drop across the diffuser, especially if it is a ceramic defuser. And, that is not good at all.

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post #10 of 11 (permalink) Old 12-16-2014, 10:57 AM
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co2 amount one bubble holds is not constant, it depends on pressure.
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post #11 of 11 (permalink) Old 12-17-2014, 04:02 AM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
3 psi is too low for the output from the regulator.
Yes, the single stage regulator was really having trouble holding setpoint and that coupled with the needle valve issue just drove me to get a completely new set up.
The new one is a low pressure two stage regulator. The outlet range is only 0.1 to 2.0psig. I have it set to 0.5psig. It works well with my injection set up.

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