Digital Pressure Adapter

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cafeIKE

Postby cafeIKE » Apr 27, 2007, 2:18 pm

As Newton said "If I have seen further, it is by standing on the shoulders of giants."

First Cannonfodder hacked* the e61 thermometer adapter, then Eric Svendson brilliantly engineered the e61 Thermocouple and Thermometer adapters.

I've slightly extended their work with the Digital Pressure Adapter :

Image
Brew Pressure during an actual shot.


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Pump Pressure on the Vibiemme on a blind basket.


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Pressure on the Blind Basket. (Note the droplet at the gauge / SS-TA junction. The mating of the two 1/4NPT threads is rather poor. The standard two wraps of teflon tape is not cutting it here. EDIT: SwageLok SS-TA Adapter defective. Replacement does not leak with Teflon tape.)

There are a multitude of gauges available. As this is a seldom used device for a home barista, I opted for the cheap and cheerful Dwyer DPGW-09 0-200PSI / 13.8bar 500ms update. More sophisticated gauges with Min / Max, faster response, logging, etc. can be found by searching for 'Digital Pressure Gauge' on the web.

The adapter is a SwageLok SS-2-TA-7-4. Eric offers the adapter as part of his 'kit'

Which brings us to the sermon:
I'd dialed in the brew pressure long before I embarked on this escapade. The impetus behind the expenditure is to be able to accurately reset the pressure should I ever disassemble the OPV and perhaps help a friend or two dial in / diagnose a machine. The actual numbers are freaking meaningless, so I don't want any PM or posts saying I set my SS-Itai to 8.22bar and the coffee sucks. :twisted:

The extra 2d:
This adapter allows actual pressure measurements during an actual shot you can taste, which according to John Ruskin "Taste is not only a part and index of morality, it is the only morality."

*Edit : 'hack' is the highest possible praise : a person who makes things work beyond perceived limits through their own technical skill.

gscace

Postby gscace » Apr 27, 2007, 2:33 pm

cafeIKE wrote:Which brings us to the sermon:
I'd dialed in the brew pressure long before I embarked on this escapade. The impetus behind the expenditure is to be able to accurately reset the pressure should I ever disassemble the OPV and perhaps help a friend or two dial in / diagnose a machine. The actual numbers are freaking meaningless, so I don't want any PM or posts saying I set my SS-Itai to 8.22bar and the coffee sucks. :twisted:

The extra 2d:
This adapter allows actual pressure measurements during an actual shot you can taste, which according to John Ruskin "Taste is not only a part and index of morality, it is the only morality."



Yeah, the pressure difference between pumping against a blind filter and pumping thru a coffee cake is often very large. It's also machine specific, varying between types of machines, and sizes of gicleurs. I tested a machine that had a 4 bar difference between static pressure and dynamic pressure. Measurements were made using the same gauge, so gauge calibration wasn't an issue.


-Greg

User avatar
erics

Postby erics » Apr 27, 2007, 4:51 pm

Great Job Ian !

Please note that this adaptor is only for use with the thermometer adaptor (the one designed for 1/8" tubing). The thermometer adaptor can also be purchased with an "enhanced kit" (~ $4) which will allow for the easy interchange of the thermometer for a more accurate and responsive 1/8" thermocouple. The kit which Ian designed and discusses would cost about $11.

Full details would be found here: http://users.rcn.com/erics/
Skål,

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

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cannonfodder
Team HB

Postby cannonfodder » Apr 27, 2007, 6:24 pm

I would like to have one of Greg's Thermofilter with an installed pressure transducer and adjustable outlet so I could simulate the pressure under flow along with the extraction temperature. One house payment would cover the PF, fluke and digital pressure meter.
Dave Stephens

User avatar
cafeIKE

Postby cafeIKE » Apr 27, 2007, 6:43 pm

cannonfodder wrote:I would like to have one of Greg's Thermofilter with an installed pressure transducer and adjustable outlet so I could simulate the pressure under flow along with the extraction temperature.

I opted for the 'on the puck' pressure measurement as it changes during the extraction.

If I was a bit more twisted, I'd probably hook up one of the AST Sensors from the lab, write a bit of software to kill the shot at the optimal point as the pressure just begins to knee. :wink: Nah, it's only coffee...

cannonfodder wrote:One house payment would cover the PF, fluke and digital pressure meter.


Out here, one house payment includes an A3. :lol:

User avatar
cannonfodder
Team HB

Postby cannonfodder » Apr 28, 2007, 12:54 am

My house payment is not quite that much. :roll:
Dave Stephens

pszilard

Postby pszilard » Apr 28, 2007, 7:45 am

Well done Ian, for pushing the envelope!

I went on an "Advanced Barista" course today where we all took our own machines and had mine checked for brew pressure using a 3" diameter pressure gauge fitted to a blind PF. It showed 1 bar less than the VBM's built in gauge, which is similar to your finding.

The instructor found the VBM really tricky to setup. We ran the same coffee/grinder on the Domobar Super and an ECM Giotto and both had the exact same brew pressure, yet the VBM was flowing too fast. Hence my other post about the restrictor.

The Domobar aced all other machines with it's single nostril frothing spout :lol:
Paul Szilard