?ing Push

[pvs6]

As I understand the theory, say a beer was kegged @13 PSI and that is the required pressure at 38 F. when the gas is in balance, But some say to add 1 pound pressure or 14 Psi for "Push". Again as I understand it the "Push" is to offset the resistance of the beer passing through the beer line and being slowed down by friction contact with the edge or wall of the beer line. Also though less mentioned it would offset the rise in elevation from the beer level in the keg to the tap.

I must be missing something and so ask to learn what it is. As I see it elevation or keg to tap is a constant, and takes a certain given amount of thrust (in this case pressure) to over come gravity.

Regarding beer line resistance: I've doubled my length and slowed the flow noticeably. But I doubt I cut it in half (flow per minute) and doubt it's a linear effect guess I can check the resistance charts to confirm this. But this does prove there is beer line resistance in play.


Here's what trips me up and I need help with. Personally I have a 1 & 1/2 F. temp. degree gradient between the units bottom and top. Also a 6 & 1/2 F temp. difference between bottom and tower tap, and 1st. pour is good very close to 2nd. But let's imagine a perfect world where all temps. are the exact same; bottom, top and tower. WHY do I need "Push"? To off set gravity and resistance? If so as I see it the only time those 2 factors come into play is when the tap is open and that in the lifetime of a keg is a very very small percent. Pretty much the constant state of my keg is tap closed so there is no gravity to overcome the beer is already up there and in a closed system there is no need for thrust to counteract gravity. The beers not moving either so resistance is a moot factor also.

I uses to add the 1 pound Push but have recently upon reflection of all this quit. I have ascertained no ill effects. So why push?

1) If it's for resistance slowing my pour, then shortening my line works as well. If it's for gravity, uphill push then since I was after a slower pour anyway the rise works to my benefit.

2) What little time the tap was open for is quickly adjusted for by the Co2 infusion to steady state pressure.
My premise is if 13 Psi is the correct kegged and current temp. pressure then there is no need to Push.

3) What harm am I doing by not pushing? Breakout? Can't see how if the temp. were constant and the line is sealed when tap is closed the pressure through out would remain the same in theory. So no breakout. Flow speed correctly controlled by line length not pressure so why change PSI?

[psychodad]

I've never added any "push" to my system. While I can see this being something to maintain cabonation at the ballpark or large bars where the tap is opened and closed constantly there is likely little or no benefit for us home tappers who draw a few beers every evening or so.

[pvs6]

I've never added any "push" to my system. While I can see this being something to maintain cabonation at the ballpark or large bars where the tap is opened and closed constantly there is likely little or no benefit for us home tappers who draw a few beers every evening or so.

Thank you, that's what I'm coming to believe also. It comes in to effect when the tap is opened every few minutes like you said in high volume venues. But it has no bearing for home users, and in fact could slightly over carb. the beer. Most of the people wanting help here are home users so why is Push (a volume venue function term) so often included here where it's not needed without the disclaimer that it applies to short life kegs?

[psychodad]

Most of the people wanting help here are home users so why is Push (a volume venue function term) so often included here where it's not needed without the disclaimer that it applies to short life kegs?

I don't know that there is a call for a disclaimer. My reasoning for there not being a need for 1 psi of push is merely my theory. Scott will be able to elaborate if he reads this.

[cubby_swans]

I've always seen Scott explain it as you add 1lb to compensate for the loss in pressure that occurs when you open the tap handle.... but I've never added anything either.

[Scott Zuhse]

"Push" has been used for decades at retail as it compensates for the pressure drop associated with an open faucet. A keg that has a specific carbonation level at a specific temperature will exert a specific pressure in the sealed head space of the keg. That head space is no longer sealed when the faucet is open.

If your PSIG against the beer is equal to the head space pressure (equilibrium), the gas in the beer will tend to leave as you dispense causing a pour that may be slightly streaky (not clear). If your PSIG against the beer is slightly higher (push) than equilibrium pressure at the head space, the gas in the beer is less likely to break out. One pound for home dispense is ideal as often your volume is lower than retail (maybe). Two pounds for retail as their volume tends to be higher (not always).

Most individuals would have a hard time picking up any flavor issues with a carbonation change at the bottom of the keg and this higher carbonation would not cause dispensing issues. Three or higher "push" pressure would be a different story.

Brewers years ago would utilize "push" in reverse when they filled the older style kegs that had a bung. They would pressurize an empty keg with the beer's "rack" pressure (equilibrium) and then pressurize the beer flowing into the keg with a slightly higher pressure to control the carbonation as the keg filled. They also employed "bung hole sniffers" That's a job title you would not want to wear!

The tubing really does not have an impact on this as all it does is transport the product from the keg to the faucet while hopefully maintaining quality and controls the speed of the beer flow from the faucet. If the dynamic pressure against the beer as it passes through the system equals the PSIG propelling the beer, fluid control tells us that are flow speed will be very close to a gallon a minute.

Now, if you choose to not use any "push", be aware that you risk having a little more of a dispensing issue than not utilizing this practice. Additionally, beer that has lost carbonation is easier to detect a flavor change than over carbonated. Although, if you are satisfied with how your system is set up now (Cubby), I defer way, way, way back to my first instructor Lyle - "If it ain't broke, don't fix it"