SS Brewtech Unitank pressure test

[birzzz]

Hi,

I've just purchased an SS Brewtech Unitank 7 gallon. I've cleaned it thoroughly per instructions. I then performed the leak test with liquid above all bottom ports and added about 10PSI of pressure. No leaks whatsoever. Then, I emptied the vessel and put 10PSI of pressure and monitored the gage for the next couple of hours (SS Brewtech says it shouldn't drop by more than 3PSI) After about 4 hours, the pressure was down to 0 PSI. I made sure every valve was tightly closed and also put some soapy water on the PRV to find obvious leak, nothing there either. I tried several times and always made sure everything was tight, with the same results...

Is it the CO2 being absorbed by the volume of air or I am indeed having a leak that I need to find out?

I have contacted SS Brewtech support, but no answer from the m yet, any input from you guys would be appreciated.

Regards,

 

[Vale71]

If you dumped all the water then there is nothing in there to "absorb" CO2 so pressure should hold indefinitely, if it doesn't then you have a leak. Make sure everything is tightened properly and start spraying every attachment with soapy water.

 

[Broothru]

If you dumped all the water there there is nothing in there to "absorb" CO2 so pressure should hold indefinitely, if it doesn't then you have a leak. Make sure everything is tightened properly and start spraying every attachment with soapy water.

+1. There's got to be a loose fitting or valve cracked open somewhere. I believe SS does their own final testing before they ship at somewhat above 10 psi (up to as much as 60 psi IIRC). 'Normal' operating pressure is 15 psig (~ 1 atm), and their instructions say not to exceed 20 psig. The placard says never exceed 30, and I remember somewhere reading they tested to 60 without deformation or failure. Wouldn't want to be anywhere near that tank when they did. BTW, the PRV on the lid opens somewhere around 22 psi. Never operate under pressure without that fitting in place! What isn't clear is whether every unit gets tested or just the prototype or random production models get tested, and to what maximum pressure.

But like Vale71 said, the only explanation is a leak somewhere. Did you undo any fittings or maybe not fully close a butterfly valve after draining? I've got 12 TC fittings on mine in the final configuration and it's really a chore getting all the gaskets straight and not pinched.

It may be a silly question but did you remove a higher top side fitting before you emptied the tank after performing the 'wet' pressure test? That might be a likely culprit. If you didn't remove a top fitting, you may have created a negative pressure vacuum that partially sucked in a gasket that now allows pressure to release. Unlikely but possible.

One really obscure possibility might be the oxygen stone fitting. If the mini valve is open you might be getting reverse diffusion across the scintering surface and venting outside the tank. Simple fix. Close the valve.

Other than that, you may have to remove every fitting and every valve and carefully reassemble, maybe applying CIP film to the gaskets. Then do the soapy water test that Vale71 suggested. It's a time consuming task, but it's the only way to find where the leak is. And it has to be a leak.

Brooo Brother

 

[Jtvann]

+1. There's got to be a loose fitting or valve cracked open somewhere. I believe SS does their own final testing before they ship at somewhat above 10 psi (up to as much as 60 psi IIRC). 'Normal' operating pressure is 15 psig (~ 1 atm), and their instructions say not to exceed 20 psig. The placard says never exceed 30, and I remember somewhere reading they tested to 60 without deformation or failure. Wouldn't want to be anywhere near that tank when they did. BTW, the PRV on the lid opens somewhere around 22 psi. Never operate under pressure without that fitting in place! What isn't clear is whether every unit gets tested or just the prototype or random production models get tested, and to what maximum pressure.

But like Vale71 said, the only explanation is a leak somewhere. Did you undo any fittings or maybe not fully close a butterfly valve after draining? I've got 12 TC fittings on mine in the final configuration and it's really a chore getting all the gaskets straight and not pinched.

It may be a silly question but did you remove a higher top side fitting before you emptied the tank after performing the 'wet' pressure test? That might be a likely culprit. If you didn't remove a top fitting, you may have created a negative pressure vacuum that partially sucked in a gasket that now allows pressure to release. Unlikely but possible.

One really obscure possibility might be the oxygen stone fitting. If the mini valve is open you might be getting reverse diffusion across the scintering surface and venting outside the tank. Simple fix. Close the valve.

Other than that, you may have to remove every fitting and every valve and carefully reassemble, maybe applying CIP film to the gaskets. Then do the soapy water test that Vale71 suggested. It's a time consuming task, but it's the only way to find where the leak is. And it has to be a leak.

Brooo Brother

There's no better answer out there.

 

[birzzz]

Hi guys,

I managed to fix it in the end. It was the bolts on the blowoff cane ball valve that were slightly loose. After tightening them up, no more pressure drop.

Thanks for your help!

 

[Broothru]

Hi guys,

I managed to fix it in the end. It was the bolts on the blowoff cane ball valve that were slightly loose. After tightening them up, no more pressure drop.

Thanks for your help!

Good find. That explains why you saw no liquid "below the water line" of the welded TC ports, since the TC port for the blow off is at the top of the tank.

It would have driven me nuts trying to find that particular leak point. Bolts on a ball valve! Who woulda thunk?

Brooo Brother

 

[Qhrumphf]

The only other thing I could think would be temperature. If your water and as a result the tank were extremely hot, the pressure will drop as it cools.

You found the issue, so that's obviously not the case.

But a related concern to keep in mind. Hot tank, sealed, and allowed to cool has the potential to collapse a tank.

 

[Qhrumphf]

(i don't know if SS Brewtech tanks are vacuum rated, but many out there aren't)

 

[birzzz]

At first I ruled out the ball valve since it had a tube submerged in water and I saw no bubble. But since the leak was prior the ball valve itself, that is why it took me some time to figure it out. Glad I found it

And as you said, they aren't rated to support any vacuum.

cheers!

 

[Broothru]

(i don't know if SS Brewtech tanks are vacuum rated, but many out there aren't)

I had thought the factory PRV (the detachable 3" TC top mounted one) was also negative pressure relief, but I can't find any reference to back that up. People don't appreciate how easily a positive pressure rated tank can collapse like a Coors lite can under a very small negative vacuum. Ever see the leftovers of a 6,000 gallon fuel truck that had a failure of a negative relief PRV fail to open? Hint: it ain't pretty.

Brooo Brother

 

[Tom R]

I had thought the factory PRV (the detachable 3" TC top mounted one) was also negative pressure relief, but I can't find any reference to back that up. People don't appreciate how easily a positive pressure rated tank can collapse like a Coors lite can under a very small negative vacuum. Ever see the leftovers of a 6,000 gallon fuel truck that had a failure of a negative relief PRV fail to open? Hint: it ain't pretty.

Brooo Brother

Just for insurance in case I did something stupid, I bought one of these PRVs that also protects against implosion.
https://www.brewershardware.com/Tri...er-15-PSI-TC15PRV15-1_51.html?category_id=375

I haven't tested it under vacuum, but it opens reliably at 14 PSI, and closes at 13.5 PSI.
I like that it is huge, I can't imagine that it could ever be clogged with krausen.

It's kinda spendy, but I like the peace of mind it gives me.

 

[Qhrumphf]

I had thought the factory PRV (the detachable 3" TC top mounted one) was also negative pressure relief, but I can't find any reference to back that up. People don't appreciate how easily a positive pressure rated tank can collapse like a Coors lite can under a very small negative vacuum. Ever see the leftovers of a 6,000 gallon fuel truck that had a failure of a negative relief PRV fail to open? Hint: it ain't pretty.

Brooo Brother

Oh pumping out of a sealed unvented container that can't tolerate negative pressure is asking for calamity.

 

[Broothru]

Oh pumping out of a sealed unvented container that can't tolerate negative pressure is asking for calamity.

In a former life (I.E., before becoming a retired person of leisure) I use to fly pressurized aluminum tubes stressed to a nominal differential of 8.5 to 9.5 inches positive. The negative pressure relief however would trip somewhere under 2" hg. You wouldn't want your airplane imploding mid-flight after all.

Brooo Brother

 

[Broothru]

Just for insurance in case I did something stupid, I bought one of these PRVs that also protects against implosion.
https://www.brewershardware.com/Tri...er-15-PSI-TC15PRV15-1_51.html?category_id=375

I haven't tested it under vacuum, but it opens reliably at 14 PSI, and closes at 13.5 PSI.
I like that it is huge, I can't imagine that it could ever be clogged with krausen.

It's kinda spendy, but I like the peace of mind it gives me.

Good insurance, indeed. Did you see that PRV opens at 15 psig , but the negative pressure relief breaks at 1.5? Pressure vessels can withstand significantly greater positive pressure than negative. That PRV protects you both ways.

Brooo Brother

 

[Qhrumphf]

Most decent PRVs should be anti-vac as well.

But I'd never rely on anti-vac to save me, much like I'd never rely on a PRV. Hot vessel either gets vented or put under pressure to cool down.