Building a Portafilter Pressure Gauge

[TroyR]

So I ran off and bought a pressure gauge, elbow and adapters to piece together a portafilter pressure gauge for myself.

When I got home and put it all together, I realized (eventually) that my current configuration of: basket -> portafilter -> 3/8"x3/8" elbow -> 3/8"x1/4" adapter ->1/4"x1/8" adapter -> 300 PSI gauge just wasn't going to work.

I had completely forgotten that I do not have a seal between the basket and the portafilter itself!
Lets not worry (for now) about the fact that I have forced together the 3/8" parallel threads of the portafilter and the 3/8" NPT on the elbow.

Does anyone have any advice to make a seal between the basket and portafilter?

Cheers,
Troy

[HB]

Does anyone have any advice to make a seal between the basket and portafilter?

Why not remove the basket? The portafilter should seal against the gasket without it.


Bob Roseman's DIY portafilter gauge (link)

[TroyR]

My stock Bezzera PF has a two notches in the lip positioned near the centre of each ear. Apparently this is not common I guess.
My bottomless PF has no notches, but that presents a whole new set of problems for this application.

[HB]

Too bad, the old Rancilio portafilters for Silvia had similar notches. In the photo below, its blind basket is drilled:


alt.coffee's traveling portafilter, current whereabouts unknown

I've seen photos of similar portafilters with the notch brazed over (example). I wonder if a big, thick o-ring under the basket rim would get a good enough seal to measure the pressure. While not a direct answer to your dilemma, Testing Brew Pressure offers some other options.

[TroyR]

Thanks Dan, I kind of like the idea of T'ing in rather than (or before) brazing the notches. Since the panels need to come off anyway to make the adjustment it shouldn't matter if the gauge is external or internal.
With a 116 deg C max operating temp the gauge should even be able to reside inside the machine.
Cheers,
Troy

[cannonfodder]

[GRB]

[Designer]

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Hi GRB, Is that a needle valve?

[GRB]

Hi GRB, Is that a needle valve?

Yes. Allows me to simulate the shot flow and measure pressure at the same time.

[TroyR]

Well, I found a post on CG (I think) that said the poster was able to get a Bezzera PF to seal with the basket using Teflon tape around the outer side- wall of the basket.
Sure enough, 3 miles of Teflon tape later I got a seal between my single basket and the PF. Now just to dial it in, the stock OPV setting was ONLY 13 bar.
It was surprising to see how the pressure ramps up slowly though, I thought it would have been quicker than it is. Granted, this closed system is entirely different than a basket of coffee.



Troy

[sygyzy]

I am going to add Chris Coffee to the list!

[timo888]

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

[TroyR]

An o-ring with a small cross-section, to fit between basket wall and PF wall?

Regards
Timo

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]

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]

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

[TroyR]

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.

[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.

[TroyR]

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.

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

[erics]

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).

[TroyR]

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).

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