Building a Portafilter Pressure Gauge - Page 2

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sygyzy

#11: Post by sygyzy »

I am going to add Chris Coffee to the list!
Peace!
Sygyzy

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timo888

#12: Post by timo888 »

TroyR wrote:Does anyone have any advice to make a seal between the basket and portafilter?
An o-ring with a small cross-section, to fit between basket wall and PF wall?

Regards
Timo

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TroyR (original poster)

#13: Post by TroyR (original poster) » replying to timo888 »

If you could find one the right size I don't see why it wouldn't work. I just wrapped a ton of teflon tape around the outer wall of the basket until it fit tight enough to hold 13 bar.

gscace

#14: Post by gscace »

Designer wrote:Hi GRB, Is that a needle valve?
Ya gotta put something in to simulate flow or you get the wrong pressure answer. In some machines this can be a very large error. The error is largest on vibe pump machines where a significant fraction of the total flow goes through the coffee cake. In one case I measured a difference between the static pressure reading and the reading under simulated flow conditions of over 60 psi (that's 4 bar).

-Greg

PaulTheRoaster

#15: Post by PaulTheRoaster »

A few rubber bands also works nicely to seal the filter against the portafilter.

TroyR (original poster)

#16: Post by TroyR (original poster) »

gscace wrote:Ya gotta put something in to simulate flow or you get the wrong pressure answer. In some machines this can be a very large error. The error is largest on vibe pump machines where a significant fraction of the total flow goes through the coffee cake. In one case I measured a difference between the static pressure reading and the reading under simulated flow conditions of over 60 psi (that's 4 bar).

-Greg

Wow. Next revision coming up I guess.

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erics
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#17: Post by erics »

Nice choice in gage.

And the next revision should be super simple - instead of the 90 ell you have connected to the PF, simply use a 3/8" tee. On the bottom leg of the tee, screw in a needle valve or whatever such that you can simulate YOUR chosen flowrate through the coffee puck. A very acceptable standard rate is 3 ml/sec which equates to putting 60 ml in the cup and leaving 15 in the puck in 25 seconds - and then you can play from there.

And, as Greg S. says, in some machines the delta between a static pressure measurement and a measurement under some reasonable flow conditions can be shocking. In most cases, it may be just right to simply set the OPV to 9.0 bar under zero flow conditions and enjoy the brew at 8.5 bar or whatever. In other cases, it can be less than rewarding.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

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TroyR (original poster)

#18: Post by TroyR (original poster) » replying to erics »


Thanks, $30 ish CAD at ColeParmer.ca for the gauge.

Actually, I have yet to convince myself that dialing down my OPV from 13 bar to anything else is a good idea (or at least that it will make a difference to most of my shots). I am of the mind that a good shot will naturally create a system pressure in the 8 or 9 bar range and that the 13 bar OPV is a max limit for the system to allow flow and prevent damage in the case of a choked system.
Anybody want to support that or change my mind?


Regards,
Troy

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erics
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#19: Post by erics »

TroyR wrote:Anybody want to support that or change my mind?
It is an interesting discussion and has been bandied about here in about a dozen or so posts in addition to the wisdom that is written in the "how-tos" on this site.
A lot depends upon the exact pump you have in Mr. B and whether or not there exists other "things" within the machine to reduce this pressure.

Why not simply try it for yourself - both ways ? i.e. note the time and volume of a "favorite" shot and then adjust the OPV and grind setting to achieve similar time and volume on another shot(s).
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

TroyR (original poster)

#20: Post by TroyR (original poster) » replying to erics »


That's the plan, I didn't reeeaaly want to start another discussion on that particular topic either.
Cheers,
Troy