# Why Are Corny Kegs Rated To ~130psi?



## seravitae (18/12/09)

Hey guys,

Just wondering, corny kegs are obviously rated to 120-130 psi (as so inscriptions tell me) however I was wondering why they are rated this high. Surely in factory (when used with cola) they are filled with pre-carbonated cola and as such are probably under very little pressure (maybe if the kegs get warm but not much pressure increase).

I think it may just be a function of the thickness of the stainless (any thinner and it wouldnt be suitable for transport) and the quality of the welds/seals - not the application itself, but I'm not sure.

I ask because i've seen people make party kegs out of those pressure spray bottles (which i really doubt would last at 130psi, maybe 40 tops)... Is there any problem if I find a suitable vessel to make a party keg, if it can only withstand serving pressure (and I don't force carbonate at high pressure)? Or do I really need a vessel that can handle 130 psi...

Cheers,

Seb


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## real_beer (18/12/09)

sera said:


> Hey guys,
> 
> Just wondering, corny kegs are obviously rated to 120-130 psi (as so inscriptions tell me) however I was wondering why they are rated this high. Surely in factory (when used with cola) they are filled with pre-carbonated cola and as such are probably under very little pressure (maybe if the kegs get warm but not much pressure increase).
> 
> ...


Not a technical answer but something to think about.

A lot of equipment is over engineered to fulfil an anticipated long work life. Using a passenger jet as an example, each time its pressurised the whole of the fuselage expands like your chest as your lungs fill with air, and then returns to normal as the pressure is released. They design the aircraft to be able to do this safely for X many times before metal fatigue and wear and tear become a problem, when this point is reached it's safer and cheaper to build a new plane than try to keep maintaining an old one. 

It's the same story with all types of gas cylinders which also have corrosion to be taken into consideration. 
One interesting show I saw on tv about 30 years ago showed them pressure testing the old stye 750 ml Coca Cola bottle (they were really thick and you took them back to the shop to get a refund on the empty bottle). Well it turned out it was the most over engineered container in the world (safety wise), I can't remember if it was that it took 2500 psi to break it, or that it could take 2,500 more pressure than it was used for. It was very impressive too watch them test it!

Another reason might be that although something could be safely designed to a lower standard they take into account some people might try to use it for something it wasn't originally designed for. When the corny kegs were used commercially the places that had them installed would have had all the gas bottles, regulators, valves etc. professionally installed as well, well within safety guidelines. On the other hand an inexperienced home brewer could hook one up and blast huge pressure into one before realising their mistake, and it doesn't take long for one to reach way over the serving pressure :icon_cheers: .


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## katzke (18/12/09)

Do not know the real answer but I run my soda water at 45psi. I would go higher if I could.

The test pressure is the normal use pressure multiplied by a safety factor.


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## MarkBastard (18/12/09)

Weren't these designed to hold a relatively thick syrup rather than the actual finished product soda?


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## samhighley (18/12/09)

Mark^Bastard said:


> Weren't these designed to hold a relatively thick syrup rather than the actual finished product soda?



I believe so. They held a thick syrup which was mixed with water and carbonated in-line.


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## MarkBastard (18/12/09)

Sammy said:


> I believe so. They held a thick syrup which was mixed with water and carbonated in-line.



So you'd probably need a decent pressure to move thick syrup through a cornie keg I'm betting...


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## jayse (18/12/09)

I imagine the syrup line would be very long also and have quite a bit to it for all the mixing and what not so would have quite a lot of resistence and need a lot of pressure to get it to the tap in the bar. I would imagine at a guess you could use aircompressor on the syrup tank possibly, the carbonation is not done in it when used like that.
Similiar to a commercial beer chilling and serving set up they require much more pressure then a corny keg in a fridge with just a couple metres of line.


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## katzke (18/12/09)

Sammy said:


> I believe so. They held a thick syrup which was mixed with water and carbonated in-line.



They were also used for premixed soda. Less equipment needed and very portable. You can serve permix with only CO2 and ice. If you use syrup you need CO2, water, and power to run the carbonator.

Not sure if you can still buy premixed soda but it was used.

Also the syrup still has to be above the same presure as the water and CO2 used to carb up the drink at the point it hits the carbonator.


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## bear09 (18/12/09)

Dont want to sound rude at all but - who cares?

Make we need for beer is going to be what - 40-50 MAX MAX...

I only ever go to 15.

I take comfort in the fact that its rated to 130. It would make me nervous if it was rated to 30-40..

In regards to capacity more is always better as it improves your saftey buffer.


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## Pete2501 (18/12/09)

To keep out the rabbits.


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## bill_gill85 (18/12/09)

bear09 said:


> Dont want to sound rude at all but - who cares?
> 
> Make we need for beer is going to be what - 40-50 MAX MAX...
> 
> ...



To be honest, I think the OP does care. They wanted clarification if a pressure vessel for dispensing beer that is carbed at serving pressure needed to be rated at 130psi.

Sera,

The pressure sprayers that people use don't have any visible rating & I don't think that anyone from here has done any destructive testing. The PRV in the sprayers appear to operate at about 20-25 psi, sufficient for the average beer, carbed at serving temperature. I wouldn't attempt to modify the PRV unless you know enough about pressure vessels & hydrotesting.

I don't think that people have looked for a different vessel, the pressure sprayers are easy to modify & cornies arent too expensive if you want a standard size keg.

Cheers,

Ben


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## Darren (18/12/09)

Whats the maximum pressure to come out of CO2 bottle (if by chance the maximum was delivered to a keg)?

cheers

Darren


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## Pete2501 (18/12/09)

The internet is a liar so take this at a grain of salt. 

http://www.aquariumlife.com.au/showthread.php?t=14206

A post in the above link suggests over 900psi in a bottle.


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## seravitae (19/12/09)

Thanks for the posts guys!






> To be honest, I think the OP does care. They wanted clarification if a pressure vessel for dispensing beer that is carbed at serving pressure needed to be rated at 130psi.




This pretty much sums it up. I ask questions because I can, because I don't know the answer. I like thinking. 

For a more informative answer I am doing a design for my bar and am building a fridge into it (custom fridge) and I dont drink much but prefer to drink lots of different things. As such I would prefer to do small brews very often. A pressure sprayer (5-8L) is plenty for a 'single batch' for me, and i'd still be having a friend come round to help empty it!

I am theorizing for vessels that would be suitable as 'replacement kegs' in a long-ish term storage scenario. I was merely concerned to see if there was some reason beyond my own logic that would explain why the vessel needed to be 130 psi for this application, and the suggestions here make sense, viscosity of the syrup and very long line lengths easily justify a large pressure rating.

During this process I've decided, just as a test, to try and make a 'serving lid + dip tube thingy' for a tap-a-draft 6L plastic homebrew bottle. (one of these










They are more compact and neater than pressure spray bottles and the type of plastic is likely to be a grade better than the pressure spray bottles (obviously not a food grade app!)

anyways thanks guys for confirming essentially that I dont need to rate to 130psi. I will be carbing at serving pressure or if I absolutely must (rush?) I have cornies for force carbing and large batches.

After i've messed around with the tap-a-draft mini-keg thing, if I have success, I'll post in a new thread. Gimme a few weeks to see what i can come up with 




Cheers

Seb


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## bill_gill85 (19/12/09)

Sera,

I like your thinking with the tap-a-draft system. A possible option with the 6l pet bottles is to use a commercial carbonator cap with a normal quick disconnect. A carbonator cap is actually designed to be a universal post, it accepts both beer or gas (one at a time) so that draft beer can be taken to parties. The downside is that because it is only a single post & has no diptube, the headspace in the bottle provides dispense pressure & the bottle needs to be inverted.

It is potentially possible that with the right valving a carbonator cap could be permanently connected to gas & dispense, but this would most likely be cost prohibitive.

I haven't used the carbonator cap to dispense beer under pressure, but plan to use one on a 2L pet bottle to flush the lines on my kegging system when finished.

Carbonator Cap Maunfacturer

Ben

Edit: It seems there is no details suggesting its use for dispense, but I'm confident it would work


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## seravitae (19/12/09)

Hey Ben,

It took me a while to dig what you were saying about a single post but it makes sense. Funnily enough I was actually planning to mess around with a robotic cocktail dispenser based on inverted coke bottles with solenoids, but never considered an inverted model for serving beer!

I am happy to invert the tap-a-draught bottles to pour from. One thing that I will have to think about though is, due to the fridge behind the bar being close to the ground, and requiring gravity to pour, it may be annoying to have to do an army roll every time i want to pour a cold one heh.

Also, the tap-a-draught bottles, being obviously custom made, may have a different threading system on the neck/lids. They appear to me from photos to be quite wide and I don't know if a standard PET lid bottle cap or carbonation cap would fit on a tap-a-draft system.

That said i am really enthusiastic about your idea about the carbonation cap for carb and serve. It may be that I just bottle into 3x 2L coke bottles instead of a 6L tap-a-draft. I'm happy to do so, the bottles are cheaper (free?). I'd still like to find/rig up some sort of PET-bottle based mini-tap so I could leave a 2L in the fridge at my girlfriends place (really small fridge)

I'll keep brainstorming but you are on to something 

edit: didn't realise bronco taps were so small! would be perfect to use a bronco and just enough line to secure the tap to the carbonation cap (few cms?)


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## ausdb (19/12/09)

sera said:


> During this process I've decided, just as a test, to try and make a 'serving lid + dip tube thingy' for a tap-a-draft 6L plastic homebrew bottle. (one of these
> 
> 
> 
> ...


Do some searches on the forum about TapA-Draft, from other members posts it seems they are only good for a limited number of fill-pressurise-refill cycles before the PET plastic fatigues and they go Boomski and make a mess inside your fridge


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## bill_gill85 (19/12/09)

Sera,

Sorry about the long previous post, I've drawn a simple schematic, I hope it makes some sense, but I'll try explain.

From left to right,

1) A regulated supply of CO2 passes through a simple on/off valve (On when you are not drinking & off when you are) to keep the bottle pressurized.
2) The CO2 then flows through a check valve (note the position changed with respect to the on/off valve) to prevent any beer backflowing through the gas side.
3) The CO2 continues through a quick disconnect & carbonator cap into the inverted PET bottle (the bottle is always inverted)
4) Beer can flow backwards out the carbonator cap & quick disconnect, (but not back through the gas side due to check valve & on off valve)
5) With the pressurize valve closed, beer will flow out an open beer tap. (if the pressurise valve is open I'd expect that you would get mostly gas out the beer tap)


Things to note;

There is no PRV, therefore the assumption is a regulated CO2 supply would be used. If a suitable PRV is placed before the check valve, a keg charger type device could be used for portability & the pressurize valve would not be needed (there's one on the keg charger.)


If you have more questions, I'll try help.

Ben


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## seravitae (20/12/09)

Well, after reading the tap-a-boom thread about someone who broke his finger with an exploding bottle, it seems perhaps this isnt the best route to go.

I'm actually suprised somewhat that PET bottles go boom often (i've never heard of such happening with coopers PET bottles?)

It would have been nice to go with a tap-a-draft style system because they are quite space saving however I do value my safety and as such I think I will opt for some garden sprayers instead. Though i lose vertical height, I gain the option of having 10 fingers, and they have enough lid-room for JG fittings so I can have seperate gas in and beer out posts.

i like your idea ben, it's simple and works well, but it seems from my searches that plastic bottles aren't safe for brewing with either.. (??? should I now be ultrascared of those who cap their beer in glass?)

It's a real shame the 9L kegs are nearly $200. I suppose i'll grab some garden sprayers for the time being and slowly migrate over to the 9L's as i can afford them.


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