What PSI should a new 5 lb tank come with?

[jbb3]

I'm new to kegging and have a few questions on CO2 tank pressure...

Went to my local AirGas distributor and picked up a 5lb tank. My keezer build is still not done but I went ahead kegged a batch of Caramel Amber Ale, put it on 13psi then put the keg in my beer frig until I can complete my keezer build.

Once I rigged a single gas line to pressurize my keg, I noticed the tank only had about 725 psi when I first cracked open the valve. Is that where it should be for a full 5 lb tank @ 65-70 deg?

When I first connected the keg to the tank, it was about 65 degrees. After leaving it in my beer frig for a day and a half @ 37 deg, I went out to check it and the tank is now reading about 500 psi. Is that drastic pressure drop in psi due to the temperature drop? Or do I have a leak??

I should know whether I have a leak tomorrow. I left everything connected and closed the valve on the CO2 tank. If I have a big drop in psi in the keg, I guess I have a leak somewhere...

 

[LLBeanJ]

500 PSI is about right for a refrigerated tank.

 

[masonsjax]

Temp will affect the reading and yeah that's about right. Since CO2 is liquid when under pressure, that gauge doesn't tell you anything useful as it's only showing the pressure of the headspace inside the tank that's occupied by gaseous CO2. It will stay at the same pressure until the liquid has depleted and there's only gas left inside, then the gauge will quickly plummet to zero.

 

[day_trippr]

Cheers!

 

[UpstateMike]

Think of the high pressure gauge on the regulator as the low fuel light in your car. It will not tell you how much CO2 you have, but when it starts to drop, you are already out of liquid CO2 in the tank and running on fumes.

 

[jbb3]

Thanks All I feel better! At first I thought I got shorted on the tank fill, then wondered if I had a bad leak.

Last night, with the keg pressure set at 13 psi, I turned the valve on the tank off but left everything hooked up. This morning I checked it (about 10-12 hours) and the high pressure gauge was on 0, the low pressure gauge was around 7 psi. Seems like I have some minor leakage. Is that about normal or should it hold closer to the set psi for longer that that??

 

[ChuckO]

You can't tell if you have a leak or not from what you described. Some high pressure gauges are very inaccurate and 7 psi might not register on a gauge with a scale that goes up to 1000 psi or more. You might have had CO2 go into solution in your beer enough to lower the pressure to 7 psi. It would be easier to test for a leak by disconnecting the keg, opening the tank valve, set the regulator for 30 psi, closing the tank valve and waiting a day. If the either gauge goes down then you have a leak.

I did this before I had a beer ready for the keezer and the high pressure gauge stayed at 650 psi for 2 weeks before I had the beer ready to go.

 

[UpstateMike]

Once I rigged a single gas line to pressurize my keg, I noticed the tank only had about 725 psi when I first cracked open the valve.

When I first connected the keg to the tank, it was about 65 degrees. After leaving it in my beer frig for a day and a half @ 37 deg, I went out to check it and the tank is now reading about 500 psi.

the high pressure gauge was on 0

If the high pressure gauge is reading 0, the tank is empty.

 

[vincentAlpha]

If you have a scale handy that can go up to 10-20lbs stick the tank on there. The weight of the tank will vary by manufacturer but mine is about 7lbs empty(also it is aluminium). If you are close to that you may have sprung a leak somewhere.

 

[solbes]

Normally I'd say those gages are fairly worthless (high pressure tank gage). PV = nRT, yes it will have less pressure at lower fridge temps.

But if its reading 0 it would appear you have a leak (assuming you have a good gage). And maybe not a slow one. I think its always a good idea to spray starsan around all fittings, especially when you get a new tank/regulator/hose/keg setup. You will see bubbles form anywhere there is a leak. Can save you $20 in CO2.

The reading of 10-13 psi in your keg last night and 7 this morning could just indicate that the CO2 has not yet reached equibrium (i.e. still carbing up). Cheers

 

[Rev2010]

I've only gotten two hooked up since I've only been kegged since October, but yeah both of mine read 500psi when full at 36F. Keep in mind it will stay at 500psi until it's very close to being fully empty at which point the needle will then drop. You might want to consider keeping a second full tank as a spare, that's what I do, just to be sure you don't run out at an inconvenient time.


Rev.

 

[Rev2010]

Seems like I have some minor leakage. Is that about normal or should it hold closer to the set psi for longer that that??

Sounds like a leak. Also, did you make sure to open the CO2 tank valve all the way till you couldn't turn it anymore? I've read the tank itself can/will leak if you don't open the valve all the way.


Rev.

 

[masonsjax]

If the tank valve being open all the way or not causes a leak, it's broken.

You probably don't have a leak, the pressure dropped most likely because the beer absorbed some CO2. You need to unhook the kegs when testing.

 

[jbb3]

I'll try the test with the tank unhooked from the keg and see what happens.

 

[Rev2010]

If the tank valve being open all the way or not causes a leak, it's broken.

What I've read said something to the effect that it can leak around the stem if not opened all the way. Looking at the Beverage Factory instructions it also says, "Open valve "A" all the way (this is important because the cylinder valve seals in two places)." So if it seals in two places (guessing at the full open and full closed position) doesn't that seem inline with the possibility it can leak if not opened all the way?

I'm too new at kegging and CO2 tanks to say, just stating what I've read many times. If it's incorrect information do let me know so I don't parrot false info.


Rev.

 

[masonsjax]

Yeah I'm not trying flame you or anything, sorry if it sounded that way. I've just never heard of that being a problem. It's a simple needle valve, shouldn't be leaking at any position. If it does, it's either broken, or it's an inferior design. I have never had a leaky tank valve and I have never kept it at full open. I guess it couldn't hurt though.

 

[AnOldUR]

"Open valve "A" all the way (this is important because the cylinder valve seals in two places)."

This is correct. You should open the valve all the way using the same torque in the far open position as you would use when closing it. It's how these valves are designed to work. They have the potential to leak in the middle.

 

[Rev2010]

Yeah I'm not trying flame you or anything, sorry if it sounded that way.

Not at all, just want to be sure I'm not spreading mis-information. The post following mine seems to confirm this info however. All I know at this point is before I started kegging I did a ton of reading and have seen this mentioned many times including saying it will leak if not opened all the way. They say it's not the same as on something like a propane tank. I'm always open to hear more information, until then though I will continue to open all the way just to be on the safe side... and since I haven't had a single leak yet - off to a great start


Rev.

 

[Monty91]

Best way to tell how much is left is to weigh the tank, subtract the weight that is stamped on the size of the tank, and divide that difference by 5. That will give you the percentage left in the tank.

Ex. (9 lb - 7 lb stamp) / 5lb max = 40% left from full

 

[helibrewer]

If you have a scale handy that can go up to 10-20lbs stick the tank on there. The weight of the tank will vary by manufacturer but mine is about 7lbs empty(also it is aluminium). If you are close to that you may have sprung a leak somewhere.

^^^ This. The tank will be stamped with an empty weight. The tank is filled to a specified weight of CO2, 5 lbs in your case. A freshly filled tank should weigh 5 lbs more than the tare weight....pressure is immaterial

 

[jbb3]

Ok, with the low pressure gauge @ 13 psi, I disconnected the gas line from the keg and turned the tank valve off. It's been sitting there for about 10 hours. Just went to look at it and it's still @ 13 psi.

So for those that said my previous pressure drop was due to CO2 dissolving into solution; ding! ding! ding! ding! You appear to be the winners!

Thanks for the help as I figure everything out!!!



.

 

[doug293cz]

Normally I'd say those gages are fairly worthless (high pressure tank gage). PV = nRT, yes it will have less pressure at lower fridge temps.

This relationship only holds when the gas is present by itself, and then only for relatively low pressures (lower than the typical CO2 pressures we work with.) When there are both gas and liquid present in the tank, then the pressure is constant at a given temperature. Doesn't matter how much liquid, the pressure is the same. You can read the gas/liquid equilibrium pressure at various temperatures from the chart that day_trippr posted earlier in this thread.

Brew on

 

[Rev2010]

So for those that said my previous pressure drop was due to CO2 dissolving into solution; ding! ding! ding! ding!

Duh, went back and read your post, apparently I missed the part where you said you turned off the CO2 tank. Yes, that would definitely cause it to drop as the keg absorbs pressure. I thought you kept the tank open, like normal, and that the next morning your high pressure gauge was reading zero. In that event it would definitely be a leak that emptied your tank. I gotta read more attentively lol.

Rev.

 

[jbb3]

Duh, went back and read your post, apparently I missed the part where you said you turned off the CO2 tank. Yes, that would definitely cause it to drop as the keg absorbs pressure. I thought you kept the tank open, like normal, and that the next morning your high pressure gauge was reading zero. In that event it would definitely be a leak that emptied your tank. I gotta read more attentively lol.

Rev.

Don't worry about it. LOL... I write things weird sometimes too. And these threads can take twists and turns that nobody can keep up with it all, all the time...