Water in beer line after cold crash...how is this possible with positive pressure in the fermenter?

[Fidelity101]

So I had a CF5 (Spike Conical) and a Fermzilla. Both were pressurized to 15psi with a spunding valve (BlowTie Diaphragm Spunding Valve Complete Kit | MoreBeer) set to 12psi. So the spunding valves did their respective jobs and let some CO2 out and both systems settled out at 12-13psi. Everything is good up to this point. BUT...two days later I go to check on the beer prior to transfer and when I disconnect the spunding valves, I notice the line going from the spunding valve to the water jar was full of water...all the way up to and inside the spunding valve assembly. The PSI on both fermenters were 5-6psi.

My question: How is this possible? My lesson learned was to disconnect these spunding valves prior to cold crashing but I apparently don’t understand how the pressure transfer works as I didn’t think it would be pulling back UP the hose when the fermenter was still under pressure. I’ve never had this issue before but then again this is the first time I left the spunding valves attached when starting the cold crash process.

 

[Konadog]

I think you answered your own question:

So the spunding valves did their respective jobs and let some CO2 out and both systems settled out at 12-13psi.

The PSI on both fermenters were 5-6psi.

The lower pressure from cold crashing sucked back liquid. You could test this by pressurizing your fermentor to 13 PSI, put the blow off into a jar of water, then release some pressure on your fermentor and watch what happens.

 

[maxr]

A sounding valve functions like a check valve. There is no need for a water jar.

 

[Vale71]

You can play around with the attached spreadsheet (sorry, metric only) to see what pressure your fermenter will stabilize at after a cold crash. You'll need to know:

- your FV's total volume
- your beer volume
- starting pressure
- starting temperature
- final temperature

If you have very little headspace (say anything <10%) and the temperature difference is big enough you could actually end up with negative pressure (i.e. vacuum) when starting at 12-13 PSI. If you play around with the spreadsheet you'll see that the reason is CO2 moves from the headspace into the beer as temperature is lowered.

As to the reason why you had positive pressure at the end it's possible that fermentation was not done and pressure increased again after sucking back some air (which will still be in the fermenter oxidizing your beer unfortunately).

 

[Vale71]

The lower pressure from cold crashing sucked back liquid. You could test this by pressurizing your fermentor to 13 PSI, put the blow off into a jar of water, then release some pressure on your fermentor and watch what happens.

"Lower" but still positive pressure will not suck back anything, you need negative pressure (i.e. lower than atmospheric) to have suck back. If one where to conduct the experiment you propose the obvious result would be that nothing happens as pressure inside the fermenter will still be higher than atmospheric pressure.

 

[Vale71]

A sounding valve functions like a check valve.

Apparently a blowtie valve doesn't or he wouldn't have had any suckback but he might have damaged his fermenter because of the negative pressure.

 

[Konadog]

Exactly my point guys, preforming a test would prove that the blowtie is not working correctly. The only way I see liquid getting sucked back is the pressure was lowered in the fermenter (cold crash) and it sucked back thru the valve.

 

[maxr]

Apparently a blowtie valve doesn't or he wouldn't have had any suckback but he might have damaged his fermenter because of the negative pressure.

No, it really does function as a check valve, or at least it is supposed to. Watch the product videos on youtube or read the manual and you'll see that it functions just like any other spunding valve. There is a spring and a diaphram. The diaphram only opens to release excess gas pressure.

It is normal for the pressure to drop during cold crashing. The gas in the headspace will contract and the beer absorbs more CO2 because solubility increases as temperature decreases. There should not be suckback from the far side of the spunding valve though - that sounds like a defect.

 

[TLaffey]

No, it really does function as a check valve, or at least it is supposed to. Watch the product videos on youtube or read the manual and you'll see that it functions just like any other spunding valve. There is a spring and a diaphram. The diaphram only opens to release excess gas pressure.

It is normal for the pressure to drop during cold crashing. The gas in the headspace will contract and the beer absorbs more CO2 because solubility increases as temperature decreases. There should not be suckback from the far side of the spunding valve though - that sounds like a defect.

The two blowties I have both leak slightly, so once the fermentation stops I have to disconnect them (if keg posts on fermenter) or shutting off a valve I put inline. Without the added step, the fermenter pressure will fall during the final days after active fermentation has completed. When that happens, there's not enough pressure available to prevent negative pressure once cold crashed. (Refer to Vale71's comments & spreadsheet)

IMO, liquid in the line is all the evidence I need to know that the blowties alone are not sufficient to the task at hand.

BTW, I'm now using Norgren V07-200-NNLA (like this: Norgen PRV).

 

[gello22]

Neither the tube on the outlet of the spunding valve nor the air in the valve downstream of the diaphram are under pressure. So it will have suck back but only on the outlet side not the beer side. If you replaced the spunding valve with a plug the open tube submerged in water would still have suck back when cooled.

 

[Vale71]

Neither the tube on the outlet of the spunding valve nor the air in the valve downstream of the diaphram are under pressure. So it will have suck back but only on the outlet side not the beer side. If you replaced the spunding valve with a plug the open tube submerged in water would still have suck back when cooled.

Only by a couple of centimeters at most. Gas contraction due to temperature change is very small. Most of the suck-back comes from CO2 becoming more soluble and being absorbed by the beer.
This actually leads to a further hypothesis. If the blow-off was never moved once fermentation was done, i.e. its end remained underwater at all times, it would be itself filled with pure CO2 from fermentation. Once no more CO2 is being produced and pushed out through the blow-off that CO2 will start being absorbed by the water in the bucket. Given that there's a small volume of CO2 versus a presumably large amount of water the end result would be that all the CO2 would go into solution and water would be sucked back all the way to the spunding valve. Atmospheric pressure can lift water to a height of a little over 10 meters.

 

[El Duderino]

couldnt you increase the CO2 pressure in your fermenter, remove the spunding valve, then cold crash?

 

[TLaffey]

Only by a couple of centimeters at most. Gas contraction due to temperature change is very small. Most of the suck-back comes from CO2 becoming more soluble and being absorbed by the beer.
This actually leads to a further hypothesis. If the blow-off was never moved once fermentation was done, i.e. its end remained underwater at all times, it would be itself filled with pure CO2 from fermentation. Once no more CO2 is being produced and pushed out through the blow-off that CO2 will start being absorbed by the water in the bucket. Given that there's a small volume of CO2 versus a presumably large amount of water the end result would be that all the CO2 would go into solution and water would be sucked back all the way to the spunding valve. Atmospheric pressure can lift water to a height of a little over 10 meters.

In addition to the gas effects, I expect there would also be a contribution of liquid volume contraction as the beer is reduced in temperature. Using the calculator at engineeringtoolbox.com, 6G of water cooled from 20*C to 4*C will reduce in size by 0.07G, or 265ml. Depending on the size of the headspace above the beer, that could be a significant volume.

 

[Vale71]

In addition to the gas effects, I expect there would also be a contribution of liquid volume contraction as the beer is reduced in temperature. Using the calculator at engineeringtoolbox.com, 6G of water cooled from 20*C to 4*C will reduce in size by 0.07G, or 265ml. Depending on the size of the headspace above the beer, that could be a significant volume.

That will partly be compensated for by contraction of the vessel itself.