Why is this happening???

Homebrew Talk

Help Support Homebrew Talk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

k-daddy

Supporting Member
HBT Supporter
Joined
Feb 22, 2016
Messages
282
Reaction score
172
Location
Connecticut
I ferment under 10psi in my Spike CF-5 using the Blichmann Spunding Valve. Once FG is reached, my blow-off tube starts to suck the Starsan slowly up the tubing toward the pressure gauge. I have my co2 tank connected at 10psi and I can confirm positive pressure by loosening the pressure adjustment knob at the spunding valve, sending the Starsan back down the tubing. The environment in my brew room maintains a constant temperature so I can't blame it on that. Does anyone know what might be causing this vacuum where there should be none? Thanks. IMG_6744.jpgIMG_6743.jpg
 
Last edited:
That's odd . With 10psi of pressure in that fermenter there should be zero suck back. Is your tube connected to the spunding valve?
 
It could be this: The beer temperature and therefore the CO2 temp leaving the fermenter is likely slightly warmer than the ambient air temperature. So when the gas inside the blowoff tubing cools, it becomes more dense creating a slight vacuum inside the tubing.
 
It could be this: The beer temperature and therefore the CO2 temp leaving the fermenter is likely slightly warmer than the ambient air temperature. So when the gas inside the blowoff tubing cools, it becomes more dense creating a slight vacuum inside the tubing.
Thanks for the reply. I like this line of thinking but there is currently no active fermentation (bubbling) so no movement of the gas inside the tubing. I would therefore think that the tubing/gas temps are stable to the environment outside the fermenter regardless of the temp inside the fermenter. It's perplexing.
 
Is the gauge remaining constant? It seems it has to be temperature related (beer inside is getting colder). While it was active there was positive outward pressure. Once activity stopped the pressure has turned inward. But the gauge reading should be decreasing as well if this were happening.
 
Is the gauge remaining constant? It seems it has to be temperature related (beer inside is getting colder). While it was active there was positive outward pressure. Once activity stopped the pressure has turned inward. But the gauge reading should be decreasing as well if this were happening.
Thanks for your thoughts... I know, crazy. The pressure gauge hasn't moved at all. I have my co2 cylinder connected at 10psi and I maintain a constant beer temp using my temperature controlled cooling coil/glycol chiller. FYI, I just checked again... in the past 2 hours since pushing the Starsan back out of the tubing, and at constant temps in & outside the fermenter, the Starsan is once again beginning to slowly creep UP the tubing, against the gauge that reads 10psi. And yes, the gauge itself tests fine. A real head scratcher.
 
Thanks for your thoughts... I know, crazy. The pressure gauge hasn't moved at all. I have my co2 cylinder connected at 10psi and I maintain a constant beer temp using my temperature controlled cooling coil/glycol chiller. FYI, I just checked again... in the past 2 hours since pushing the Starsan back out of the tubing, and at constant temps in & outside the fermenter, the Starsan is once again beginning to slowly creep UP the tubing, against the gauge that reads 10psi. And yes, the gauge itself tests fine. A real head scratcher.
This may be naive of me, but according to the manual (https://www.blichmannengineering.com/media/manuals/spunding-valve.pdf), your CO2 supply should be 1-2psi above the pressure you've set the spunding valve for... I can't actually make sense of it myself, but have you tried setting your regulator at 11 or 12psi?
 
I'm a little confused . Why use a blow off with a spunding valve ? Having a blow off tube while pressure fermenting seems counter productive , unless that blowout off tube holds pressure up to the set point , then releases . Wouldn't it have a one way valve to prevent suck back ? I usually take off my blow off tube after a couple days and slap on the pressure valve .
 
This may be naive of me, but according to the manual (https://www.blichmannengineering.com/media/manuals/spunding-valve.pdf), your CO2 supply should be 1-2psi above the pressure you've set the spunding valve for... I can't actually make sense of it myself, but have you tried setting your regulator at 11 or 12psi?
There is a slight difference between the spunding valve gauge and my co2 regulator gauge. I set the SV @ 10psi and the regulator gauge reads 8psi... probably a built-in safety protocol but it shouldn't have any bearing on what's happening here. I have no gas leaks anywhere or I'd notice a loss of co2 at the cylinder. Maddening.
 
I'm a little confused . Why use a blow off with a spunding valve ? Having a blow off tube while pressure fermenting seems counter productive , unless that blowout off tube holds pressure up to the set point , then releases . Wouldn't it have a one way valve to prevent suck back ? I usually take off my blow off tube after a couple days and slap on the pressure valve .
I set the SV to 10psi and off-gas the excess pressure during fermentation through an empty keg to capture the co2, and from there to a container filled with Starsan. Once fermentation is complete, I disconnect the purged keg, connect the co2 cylinder to the fermenter, and drop the blowoff tubing directly from the SV to the Starsan.
 
The gas in the blowoff tube is almost pure CO2. I imagine it is dissolving into the StarSan, which has only atmospheric percentage of CO2. It will never equilibrate. This is a rare form of "suck back" not caused by dropping fermenter temperature. Anyhow, that's my best guess.
 
I'm a little confused . Why use a blow off with a spunding valve ? Having a blow off tube while pressure fermenting seems counter productive , unless that blowout off tube holds pressure up to the set point , then releases . Wouldn't it have a one way valve to prevent suck back ? I usually take off my blow off tube after a couple days and slap on the pressure valve .

The Blichmann have a hose barb on the vent port of the spunding and it's to direct any stray krausen to a place where it won't make a mess. Even after that possibility, it's nice to have the familiar glug, glug noise to tell you if it's actively venting or not.
 
The Blichmann have a hose barb on the vent port of the spunding and it's to direct any stray krausen to a place where it won't make a mess. Even after that possibility, it's nice to have the familiar glug, glug noise to tell you if it's actively venting or not.
It's a nice product.
 
Thanks for the reply. I like this line of thinking but there is currently no active fermentation (bubbling) so no movement of the gas inside the tubing. I would therefore think that the tubing/gas temps are stable to the environment outside the fermenter regardless of the temp inside the fermenter. It's perplexing.

Your mention that active fermentation had ended was what made me think that this was a possibility. Once the gas flow has stopped, it cools. Same goes for when you purge it. You would pick up some heat from the fermenter. If the starsan is open to the air, it is going to get some evaporative cooling effect and may be cooler than the contents of the fermenter.

Heat transfer from the starsan to the gas inside the tubing and the walls of the tubing creates a slight vacuum.

I like the CO2 dissolving theory as well.
 
Back
Top