Resistance of stout faucet

[bovine0001]

Anyone know the psi resistance of stout faucet? That restrictor plate must offer quite a bit and I am trying balance my draft system.

 

[Pratzie]

30 psi

 

[bovine0001]

That is the common serving pressure, but the tap itself could not be 30 or you could not push it through without increasing the serving psi to 40-50

 

[Pratzie]

Im not sure what ur asking then... What do u mean by balance out ur system?

 

[bovine0001]

http://beersmith.com/blog/2011/07/14/keg-line-length-balancing-the-science-of-draft-beer/

 

[Pratzie]

Judging by what im reading, and i may be wrong... But I think we need to know what the length's of ur lines are as well as the ID of those lines along with the height of the tap above the keg. We know the serving pressure of the keg will be 30 cuz thats what it needs to be for the faucet, but as far as the pressure at the tap, it will be variable based upon ur line's ID size, the length of the tubing and the height. Once u know that u can determine what the tap pressure is and adjust from there.

Again this is just from my reading and im by no means an expert but it seems that no matter what the tap style, it ideal pressure is slightly positive and less then 1 PSI as it leaves the spout and hits ur glass.

 

[ajdelange]

The pressure drop across a stout faucet will be

dP = (F^2)*(SG)/(Cv)^2

where dP is in psi, F is in gpm, SG is the specific gravity and Cv is the valve flow coefficient which you would have to obtain from the manufacturer or by experiment (put some water in a keg, connect the stout faucet with a short, large bore piece of tubing, dial in some pressure, open the faucet and time the flow with a stop watch).

You set the pressure on the keg according as to the amount of carbonation you want in the beer. This will depend on the amount of CO2 in the mix and the storage temperature (McDantim has some curves/calculators on their website). In an ordinary situation you would then add line until the flow rate when the valve is open is 2 Oz/sec but I don't think you need to do that here as the stout faucets (at least the classic Guiness ones) are equipped with a valve. Since you are going to force the beer through a restrictor plate it shouldn't matter that you throttled it through a valve first. Look up the classic procedure for drawing stout. It should take x seconds to fill the glass 2/3 (I think it is) full. Adjust the valve (or add choker) until you get that flow rate and I think you should be properly set up.

 

[bovine0001]

The pressure drop across a stout faucet will be

dP = (F^2)*(SG)/(Cv)^2

where dP is in psi, F is in gpm, SG is the specific gravity and Cv is the valve flow coefficient which you would have to obtain from the manufacturer or by experiment (put some water in a keg, connect the stout faucet with a short, large bore piece of tubing, dial in some pressure, open the faucet and time the flow with a stop watch).

You set the pressure on the keg according as to the amount of carbonation you want in the beer. This will depend on the amount of CO2 in the mix and the storage temperature (McDantim has some curves/calculators on their website). In an ordinary situation you would then add line until the flow rate when the valve is open is 2 Oz/sec but I don't think you need to do that here as the stout faucets (at least the classic Guiness ones) are equipped with a valve. Since you are going to force the beer through a restrictor plate it shouldn't matter that you throttled it through a valve first. Look up the classic procedure for drawing stout. It should take x seconds to fill the glass 2/3 (I think it is) full. Adjust the valve (or add choker) until you get that flow rate and I think you should be properly set up.

Ooh. Math. Could be fun.

I have my pressure set to 30 to meet the typical 2.5 volumes of co2. I use the charts rather than the calculators and feel this is set correctly. (My chemistry is good enough to understand basic partial pressure math).

I will hunt for that procedure, though it thus far is not easy to find on google. It seems like its slam it open and fill 3/4 and wait. Then crack it open to put the head.

When you say adjust valve, do you mean open it up differently? I feel like it is open or closed.

 

[ajdelange]

I have my pressure set to 30 to meet the typical 2.5 volumes of co2. I use the charts rather than the calculators and feel this is set correctly. (My chemistry is good enough to understand basic partial pressure math).

That won't give you anything close to 2.5 volumes (which is way, way too much for a stout anyway). Micromatic reccomends 38 pisg for a 25% blend. That would give you 0.25*(38 + 14.7) = 13 psia (-1.7 psig) PaCO2 which would give less than a volume. I'm away from the brewery and don't have any of my data accessible but that strikes me as about right. That's why I recommend the McDantim charts. They will tell you the proper pressure at each temperature for various blends to hit the Guiness recommendation which I think is 0.8 vols (consistent with the Micromatic numbers) but wouldn't bet the farm on that.

I will hunt for that procedure, though it thus far is not easy to find on google. It seems like its slam it open and fill 3/4 and wait. Then crack it open to put the head.

That's more or less it but I'm not sure of the details. You don't crack it for the finish though. Flow should be set up right so that the last 1/3 - 1/4 builds up support for the head from below and gives a good 'show' (bubbles flowing up).

When you say adjust valve, do you mean open it up differently? I feel like it is open or closed.

A traditional Guiness stout faucet has a throttling valve in addition to the valve that opens when you pull the lever. I tried to find a site with a picture of one but couldn't so I gather these are rare things these days and any faucet you would buy would not be equipped with one. You will, therefore, need to adjust line length to get the proper rate of pour with 38 psig blend pressure.

 

[bovine0001]

Holy crap. Apparently I don't understand the science well after all. I used the calculators and well, yeah. That's a lot of pressure. (Btw I am putting bitters through the tap hence why I was planning the higher volumes of co2, i would never do so much for stout).I guess it makes better sense to think of the amount of gas not in percentages versus volumes. I will have to plan on lesser volumes regardless as I don't want to use those pressures.

I did add about ten feet to my beer line and did see a slow down in flow but I think my challenge with this is the beer I'm putting through it is charged with enough co2 that it foams a lot when coming through the valve and plate.

I think my game plan now, seeing as I may not have the fortitude to determine my faucet resistance, I will cut back the beer line to the desired flow rate while fiddling with the valve on the faucet as well.

I appreciate all the great advice.

 

[beaksnbeer]

Stout taps don't need worry about line length. I use a 70/30 blend at 30psi on mine split to 2 taps. I pre-carb at 8psi CO2 for 2-3 weeks at 39*