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Difference in regulator and tank pressure

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  • Difference in regulator and tank pressure

    This may seem like a stupid question but, why do the regulator pressure gauges always read differently than the pressure gauges on my serving tanks?

    I set all the regulators in my walk-in to 14psi and the pressure gauges on all the serving tanks read 10psi.
    All 5 are like this. All regulators are maybe 1-1/2 to 2 years old top of the line micromatic and all pressure gauges are about the same age from GW Kent.

    Why is there a difference?

  • #2
    Have you ruled out any leaks?

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    • #3
      Don't forget about the hoses that you run to your tank. Those lines restrict the gas flow to the tank which would make for back pressure to the regulator which would result in a difference in pressure readings. I am not a physics major so this is just my thoughts. Just like most things on the web it might be right and it might not.

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      • #4
        I don't believe that leaks that would account for that much of a difference.
        Plus, I would see it in my CO2 usage and the walk-in would be full of CO2 in the morning if the tanks or lines were leaking.

        I also find it hard to believe that the gas lines themselves (which are many different lengths) could account for a 4-5psi restriction.

        Does anyone else have this happening?

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        • #5
          Originally posted by porter
          I don't believe that leaks that would account for that much of a difference.
          Plus, I would see it in my CO2 usage and the walk-in would be full of CO2 in the morning if the tanks or lines were leaking.

          I also find it hard to believe that the gas lines themselves (which are many different lengths) could account for a 4-5psi restriction.

          Does anyone else have this happening?

          I think it is safe to say that the hose lengths are different. My thoughts are that it is highly unlikely that all of your gauges on your tanks are off at the exact same amount or all of your regulator gauges are all off at the exact same amount. What is left? The hoses. Hard to believe huh?

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          • #6
            I am pretty sure that there should be zero difference while the system is closed. But the lines could affect it while gas is flowing, i.e. seving.

            just my 2 cents.

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            • #7
              If you have check valves installed they may be eating up some of your psi. They would all require the same amount of psi to open so all of your tanks would show the same drop.

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              • #8
                Rise and run. You lose psi with rise and run from the point of regulation. The farther you run a hose from the point of regulation the bigger the difference will be in psi. The rise and run are the resistance in the equation. There are many ways to deal with it. Put a regulator on each tank, or turn up your regulator to 18 or 20 or whatever it takes to get your tank to 14-15.
                Joel Halbleib
                Partner / Zymurgist
                Hive and Barrel Meadery
                6302 Old La Grange Rd
                Crestwood, KY
                www.hiveandbarrel.com

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                • #9
                  There should be no difference between what your CO2 regulator gauge reads and what your tank gauge reads in a static condition. IF you are pulling lots of CO2 (and I don't mean the slow trickle from normal dispense) then you will see a few things lead to reduced pressure delivery. One is the friction of CO2 through a hose. This depends on the line diameter, line length, and the flow rate. And this is a transient thing. As soon as the demand slows, so does the pressure difference. I'm assuming that your brewery is 10-15hl, so the flow rate at normal dispense will be low with moderate runs of gas line. Shouldn't cause a problem. The other thing is the reduction in delivered pressure of a regulator that is being asked more flow rate than it can deliver at a certain pressure. This is referred to as "droop", and why regulators come in many sizes. You don't want a tiny regulator if you're asking it to deliver 100 cubic feet/second. It just won't keep up. This is why natural gas regulators are very large and instrument air regulators are small. Again, if you have normal brewpub demands, then this phenomenon shouldn't cause much, if any, differential pressure between the regulator gauge and the tank gauge. There will be (almost) zero differential due to rise in elevation. Gas densities are miniscule compared to liquids. While this is a valid point in liquid dispense, it is not really a concern in gas distribution. One very good point that John Dean brought up is the possibility of check valves imposing a "tax" on your pressure. Most are spring operated, and require a "cracking pressure" to open them to any flow at all. This could be one or two psi, but for most dispense situations not much more. However this is not flow dependent--it will be 1-2 psi whether gas flows or not. Certainly worth removing one just for a look-see. There's also the possibility that something else is whacked. Seems remote that all the gauges would misrepresent to the same degree. Switch the regulators with a substitute (like a set from keg dispense) to see what they do. This should be a good learning experience and one that could have an easy explanation. Best of luck!
                  Phillip Kelm--Palau Brewing Company Manager--

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                  • #10
                    We experience this, but only when we're putting CO2 on the carbonation stone of our bright tanks, not when we're putting it on the headspace. When we're carbonating, the weight of the beer on the stone puts back pressure on the regulator, so the regulator pressure is higher than the tank headspace pressure.

                    So assuming that you're pushing CO2 to the headspace of the tank, not to the liquid in the tank, I have to think it's time to replace your gauges!

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