psi changes due to temperature

So I have a dual reg setup similar to this inside of the fridge. My question is does anyone know what formula or calculation to determine the equivalent psi outside the fridge? I'm not really that familiar with ideal gas laws... PV=nRT?

I know I can simply set the reg when it's at ambient temp, but say if I want to run another beer at a different psi or force carb, I need to be able to change it on the reg without having to pull it outside and waiting for it warm up to get an accurate reading.

Thanks.


http://imagehost.calabro.us/images/beer/Oster/

Set it to what ever is needed according to the keg temp and desired carb levels. The low pressure side pressure will not change the high side may read lower but it will not affect any thing.

yeah it's the liquid temp that is important, not that gas temp.

Thanks for the replies.

Here's the situation: The brew carbonates at 12psi at ~69F (room temp) - i.e. the low-pressure gauge shows 12psi. The regulator, co2, and keg are sitting outside the fridge.

I put the regulator, co2, and keg in the fridge. Fridge is set at 39F. Say it sits for a day or two. The regulator (low-pressure side) then reads ~9-10psi.

So, one way or another, the lower temp in the fridge is causing the gauge to read lower?

A large swing in the temp of the CO2 bottle can cause some pressure changes on that side. Leave the tank in the fridge and set it that way.

BTW, 12 PSI at 69F? That's very low carbonation.

So then you turn the pressure back up to 12psi. The pressure drops due to the cold.
12psi is 12psi. Temperature doesn't matter as long as the pressure is constant.

If I set the pressure to 12psi in the fridge while everything is cold, it comes out like a fire hydrant and foamy. It's only a 5' line.

I ended up by trial and error finding that setting it at about 8-9psi in the fridge keeps me from burping and beer jetting out with decent carbonation.

You really don't want to set your pressure for good pouring. You want to adjust your line length to make it pour good on a pressure that gives you the carbonation level you're after.

So, I need longer lines? They're 2ft plastic with piknik taps. I have the Oster 5.0cf fridge, I'm not sure how much I can/should lengthen the lines. Not much room with two kegs, a tank and regulator.

You need increased resistance. Search on this site for "The cure to your short hose problems", you can get some epoxy mixer inserts from McMaster Carr, very cheap, that you can put in the dip tube of the corny to increase resistance. The other option is longer lines.

longer lines (like 8' for 12psi probably, depends on the inner diameter of the line) or the things some guys are putting in their short lines.

either way you need some more resistance to slow down the beer in the line for a better pour. you don't wanna keep messing with changing the psi just to pour or re-carb for the night.

Why would they sell a keg kit with incorrect line lengths?

aar0n said:

Why would they sell a keg kit with incorrect line lengths?

Click to expand...

They expect you to use 9-10psi at 34F like most americans.

most americans?

aar0n said:

most americans?

Click to expand...

Europeans drink their beer warmer than Americans.

First result on Google: http://www.beerutopia.com/2008/06/27/what-temperature-is-your-beer/

dkershner said:

Europeans drink their beer warmer than Americans.

First result on Google: http://www.beerutopia.com/2008/06/27/what-temperature-is-your-beer/

Click to expand...

no, bmc drinkers do.

z987k said:

no, bmc drinkers do.

Click to expand...

dkershner said:

They expect you to use 9-10psi at 34F like most americans.

Click to expand...

Agreed.

That seems strange since the kit I bought came with corny kegs and I dont think you can buy/get bmc (bud, miller, coors? had to look that one up) for those.

So, back to my original question: how to determine psi difference due to temp difference? Trial and error. After pulling my reg and tank out of the fridge, the gauge read ~11psi after about an hour. Note that I kept the keg inside, still connected. I wrapped the door with a blanket and it stayed at ~39-40F. Back inside the fridge, the gauge read ~8psi. So, a ~28F temp difference throws off the gauge by about ~2-3psi.

From what I read after searching for "cure for your short hose prob" (thanks remilard), using longer lines is band-aid and therefore a terrible solution. I will be looking in to the epoxy inserts for my next keg (in secondary now).

And according to a local co that builds custom bars and kegerators, my setup is a happy medium. Thanks for everyone's input.

aar0n said:

That seems strange since the kit I bought came with corny kegs and I dont think you can buy/get bmc (bud, miller, coors? had to look that one up) for those.

So, back to my original question: how to determine psi difference due to temp difference? Trial and error. After pulling my reg and tank out of the fridge, the gauge read ~11psi after about an hour. Note that I kept the keg inside, still connected. I wrapped the door with a blanket and it stayed at ~39-40F. Back inside the fridge, the gauge read ~8psi. So, a ~28F temp difference throws off the gauge by about ~2-3psi.

From what I read after searching for "cure for your short hose prob" (thanks remilard), using longer lines is band-aid and therefore a terrible solution. I will be looking in to the epoxy inserts for my next keg (in secondary now).

And according to a local co that builds custom bars and kegerators, my setup is a happy medium. Thanks for everyone's input.

Click to expand...

Longer lines are not a band-aid, it's part of balancing your system.
http://***********/stories/techniqu...-balancing-your-draft-system-advanced-brewing
http://www.franklinbrew.org/brewinfo/balance.html
The incorrect line lengths is relative. It really depends on what you want your carbonation levels to be.

Next, as was explained, it has absolutely nothing to do with the temperature of the gas. Only the liquid. The amount of co2 water can absorb is based on the water's temperature. Therefore, if you put you tank outside your fridge, set it to 12 psi and the fridge is set to 40F, you're going to have about 2.5 volumes of CO2. If you put the tank in the fridge and set it to 12 psi, it will still be 2.5 volume of co2.

Maybe not a bandaid; Increasing pressure with inserts seems like a better, cleaner solution than cramming longer lines into my tiny fridge.

So...
gas and reg outside of fridge: gauge shows 12psi
gas and reg inside: gauge shows 8psi
The keg is inside for both. My point is that the gauge is reading different. I understand the vols aren't changing. So what's up with the gauge?

aar0n said:

Maybe not a bandaid; Increasing pressure with inserts seems like a better, cleaner solution than cramming longer lines into my tiny fridge.

So...
gas and reg outside of fridge: gauge shows 12psi
gas and reg inside: gauge shows 8psi
The keg is inside for both. My point is that the gauge is reading different. I understand the vols aren't changing. So what's up with the gauge?

Click to expand...

PV = nRT

What is changing in your system? T and P. T goes up, P also must go up since you are dealing with a constant volume.

Right. Way back in my orig post I mentioned PV=nRT. But its the low pressure gauge on the beer line that is changing when inside the fridge (Im sure the high pressure is as well).

So I guess the change in temperature of the tank/CO2 is affecting the pressure displayed on the low pressure gauge (which is connected to the beer at its fixed temp).

I guess I would have to know what's left in the tank (V) to calc the actual (as if it were outside the fridge) pressure? And then I have to deal with conversions of kpa, mols, and joules.

Once again, the easiest way is trial and error, I suppose. Crank the gas up to 25psi (what Im using for a quick force carb) outside then put it inside the fridge and see what happens.

aar0n said:

Right. Way back in my orig post I mentioned PV=nRT. But its the low pressure gauge on the beer line that is changing when inside the fridge (Im sure the high pressure is as well).

So I guess the change in temperature of the tank/CO2 is affecting the pressure displayed on the low pressure gauge (which is connected to the beer at its fixed temp).

I guess I would have to know what's left in the tank (V) to calc the actual (as if it were outside the fridge) pressure? And then I have to deal with conversions of kpa, mols, and joules.

Once again, the easiest way is trial and error, I suppose. Crank the gas up to 25psi (what Im using for a quick force carb) outside then put it inside the fridge and see what happens.

Click to expand...

The pressure regulator is not an electronic device that looks at the pressure and then decides if it should let more through. The screw is set and fixed unless you turn it. If the pressure in the tank goes down considerably, the low side will also drop. It is regulated by a spring that you essentally set the force of with the screw. If the pressure against the spring(gas from tank) drops, the spring will be able to push the valve closed more and therefore you will have less pressure coming out the low pressure side.
Because CO2 pressure is so dependent on temperature especially because of phase changes, the only way to really know what is left in your tank is weight. But this does not matter at all for our purposes except to know that you are almost out. 12psi at 40F = 12 psi at 70F. The temperature of the gas does not matter as to the volumes of CO2 retained by the liquid or to how fast or how much pressure will be coming out at the faucet. 12psi=12psi.
When you put the tank in the fridge you will have to turn up the regulator a bit to compensate for the drop in pressure off the regulator.

As far as line lengths vs inserts... your essentially doing the same thing, so sure that works. But remember, you will need different inserts just like you would need different line lengths depending on serving pressure/carb volumes. Most people find a happy medium they can serve their beer at that will cover many styles, but if you want to serve a Belgian triple at 4 volumes, it will obviously be very foamy if put in a system designed for 3.(I'm assuming you are using serving pressure to maintain these volumes)

Good god, you are way over thinking this.
Decide if you want to keep your tank inside the fridge or outside the fridge.
Then give the tank a day to equalize with whichever temperature location you decide on.
Then set the pressure you NEED for the level of carbonation you want.
Then put in beer line according to how much you need for a balanced system. The calculators all told me 3'. I put in 5 anyway. I get good pours.
Lengthening lines is not a "bandaid", it is what is needed for a proper setup.
The ID of the line is going to play a LARGE part in determining the line length.

Probably so, lol. But I'd like to throughly understand this. (This might help me more, though: http://bit.ly/cggkjT)

This is my setup:
http://imagehost.calabro.us/images/beer/Oster/

EXCEPT, I am using 5' picnic taps 3/16 (ID, right?) beer line (http://stores.kegconnection.com/Detail.bok?no=431), no tower, with this reg: http://stores.kegconnection.com/Detail.bok?no=216.

Say, I made made this beer:
http://www.ebrew.com/amber_ales/high_sierra_pale_ale.htm

Using this chart, 9psi @ 40F gives me 2.2vols, which keeps me in the green for an ale.
http://www.kegerators.com/carbonation-table.php

Coincidentally this fills a pint glass in about 7s with a little more head than I'd like.

>>> "Then set the pressure you NEED for the level of carbonation you want."

The carb level I want is what is best. I don't know enough to have an opinion.

So it looks like the best sol'n for me is to set the psi at 12 in the fridge and add inserts to slow it down.

Thanks for the patience and thorough explanation(s), guys. And hopefully I'm not making anyone's irregular-pulse worse.

You need longer lines.

The pressure changes because the mechanical innards of the regulator are cooling off/warming up, which causes them to react and regulate a bit differently...you must adjust when you change reg temp, but trust the gauge.

12 PSI at room temp is probably too low. That only gives you ~1.6 volumes of carbonation. You want something more like 25 psi (for 2.3 volumes) at room temp, then drop to ~10 PSI once in the fridge.

aar0n said:

Probably so, lol. But I'd like to throughly understand this. (This might help me more, though: http://bit.ly/cggkjT)

This is my setup:
http://imagehost.calabro.us/images/beer/Oster/

EXCEPT, I am using 5' picnic taps 3/16 (ID, right?) beer line (http://stores.kegconnection.com/Detail.bok?no=431), no tower, with this reg: http://stores.kegconnection.com/Detail.bok?no=216.

Say, I made made this beer:
http://www.ebrew.com/amber_ales/high_sierra_pale_ale.htm

Using this chart, 9psi @ 40F gives me 2.2vols, which keeps me in the green for an ale.
http://www.kegerators.com/carbonation-table.php

Coincidentally this fills a pint glass in about 7s with a little more head than I'd like.

>>> "Then set the pressure you NEED for the level of carbonation you want."

The carb level I want is what is best. I don't know enough to have an opinion.

So it looks like the best sol'n for me is to set the psi at 12 in the fridge and add inserts to slow it down.

Thanks for the patience and thorough explanation(s), guys. And hopefully I'm not making anyone's irregular-pulse worse.

Click to expand...

You have an American pale ale. For that style 2.2-2.7 is what is recommended. Pick something in that range - you said 2.2. Go to the carb chart. 2.2 volumes at 40F comes in at 9psi. Set the regulator to 9 psi.

Now to balance your system (I don't know why your so hung up on restrictors, 3/16" ID vinyl tubing is like $.5/ft at my local hardware store.)
I'll do the math for you assuming a few variables.

L = (P - (H * .5) - 1)/R

P = pressure set on regulator gauge
H = Total height from the center of the keg to faucet in feet
R = Resistance of line
L = length of beer line in feet
I'm assuming P=9psi, H= 3 ft and R = 1.8 (resistance for 3/16" ID line)

L = 9 - (3*.5) -1 / 1.8
L= 3.61ft to have a pressure of 1psi at the faucet.

In practice I find slightly longer lines than this works best.

Now say we put a Hefe in there. Now we want at least 3.3 volumes of co2 in our beer. At 40F this is 20.9psi!
Math:
L=20.9 - (3*.5)-1 / 1.8
L=9.72ft
As you can see there would now be a big problem. If you served a beer at 20.9psi in 4ft lines, it'd be nothing but foam.

Well, then. I'm using 5' lines. So I'm good! No need to change a thing. Thanks for the equation breakdown, though. BUT 2.2vols is at the bottom of the range. Is it best to keep it closer to the center (i.e. 2.4)?

For anyone who is interested, I found an excellent reference for draught systems from the Technical Committee of the Brewers Association. Check out the pdf.

http://draughtquality.org

aar0n said:

Well, then. I'm using 5' lines. So I'm good! No need to change a thing. Thanks for the equation breakdown, though. BUT 2.2vols is at the bottom of the range. Is it best to keep it closer to the center (i.e. 2.4)?

Click to expand...

Yeah, I usually go more middle of the road, that way it encompasses more styles, as I don't have a dual pressure regulator.

Also I can't remember you saying, but if you still have foamy beer with the 5ft lines, it's probably because the beer in the line rose in temperature, which brought a lot of co2 out of solution.

Also notice that H=3 was a random number that is probably far from accurate.