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$10 portafilter brew pressure gauge
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tracerbullet
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tracerbullet
Joined: 13 Feb 2012
Posts: 168
Location: Saint Paul
Expertise: I love coffee

Posted Sun Apr 29, 2012, 3:48pm
Subject: Re: $10 portafilter brew pressure gauge
 

I do have the 3-way solenoid valve, yes. I was thinking that my pressure change through the OPV may be similar to his pressure change through that valve. Perhaps not, I'll have to think about it some more. I don't mean to stray off this topic but I still wonder if there aren't similarities.

When I pull a shot, the path is: Pump, OPV, 3-way, boiler, puck. The 3-way has another path teeing from it to the drain but that is closed. (Also, the OPV actually connects to the 3-way via a tunnel through the group head, but that tunnel doesn't connect with the main chamber of the boiler, so I left it out).

When the shot is done and at any other time the machine isn't pumping, the 3-way switches position and it's: puck - boiler - drain. The path to the 3-way from the OPV is closed.

The way I'm thinking of it the OPV and the puck for my unit are in series, the 3-way is just allowing them to connect. The main restrictions are the OPV and the puck. I'm thinking the situation with this machine is similar, the spring loaded valve allows water into the boiler much like my OPV, and then it goes through the boiler to the puck also much like mine.

My OPV does release the extra pressure / water back to the pump (a CLassic dumps it back to the reservoir but ~ same thing really). I don't know about this machine, maybe it doesn't have a return at all? I so that would be a key difference and woah, yeah, I agree, totally different machines. In that case never mind my #'s and hopefully I'm not the only one that just learned something.
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AndyPanda
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AndyPanda
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Posted Sun Apr 29, 2012, 4:36pm
Subject: Re: $10 portafilter brew pressure gauge
 

Your OPV is not in series the way I meant it.  Imagine, instead, that the overflow line from your OPV valve went to the coffee puck ... that would be in series the way his spring loaded group valve is in series with the coffee puck.


Imagine putting your thumb over the end of the hose from your OPV (the overflow back to the tank)... so your thumb is applying pressure and making it harder for the water leaving the OPV to exit.  This has the effect of letting the spring in the OPV close the hole even though more than 9 bars is trying to push it open.  Your thumb pressure has added its resistance to the spring in the OPV pushing back against the pump and this changes the way the OPV valve acts and allows it to resist the pump more easily.

In the non-3-way machines ... the resistance of the coffee puck is doing the same thing as your thumb in the above example ... it is pushing back against the pump pressure so the spring has an easier time shutting the pathway and the pressure is lowered much more than the simple sum of the two resistances taken separately.

I say that the 3-way plus OPV type machine is parallel because the OPV bleeds pressure directly to the outside (low pressure) and the coffee puck bleeds the pressure inside the PF directly to the outside air - two parallel paths to the same outside low pressure air.  The high pressure water can go right past the OPV (if it were set high enough) without any interaction and exit through the coffee puck alone ... or (if the OPV were set low enough) the high pressure water could all exit the OPV with none of it going through the coffee puck at all.

I say the non-3way type machine with the spring loaded group valve is Series because the pressure must first go through the group valve on the way to the coffee puck ... so the two resistances are in series as the pressure has to go through both in turn to make it to the low pressure outside air and cannot go through either one alone (bypassing the other) and reach the low pressure outside.
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sleepdance
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sleepdance
Joined: 27 Feb 2007
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Posted Wed Jan 23, 2013, 4:18pm
Subject: Re: $10 portafilter brew pressure gauge
 

I tried this today on a Rancilio Audrey (the same mechanically as the Silvia) and can confirm that it doesn't work. The vibe pump gives too wild of a reading. I can tell that I'm between 7.5-10 bars, but nothing more precise.

edit: this was probably due to a leaky seal, not the vibe pump
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D4F
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Joined: 15 Mar 2012
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Espresso: Gaggia Classic PID
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Posted Wed Jan 23, 2013, 4:58pm
Subject: Re: $10 portafilter brew pressure gauge
 

I went through this months ago and can perhaps explain.  I built a version with a "T" so that the PF was off to one side and a valve on the other end.  I can simulate a pull of about 50 - 60 ml in 25 seconds.  I can also shut it off.  If you use a regular gauge you basically are watching the pressure pulsation of the pump with some damping of the system.  A glycerine filled gauge costs more, is a bit harder to find in some places, and is much easier to read.  The pressure sensing portion of the gauge is not affected by water in the gauge any more than by oil.  Oil has enough viscosity to damp the needle and essentially average the needle swings.  Your pressure is about in the middle of the fluctuations assuming an oscillating needle in a range, not one that is bounciing into other ranges or all over.

On the Gaggia I can isolate the water in and out by removing the supply tank and supplying water from a smaller container and measuring output from the OPV.  You can check against pressure vs flow graphs from ULKA and also get a range of pressure.  Another way to roughly set OPV and confirms that the gauge works, if that was a doubt.  Use an oil filled gauge or use about the middle of the oscillation.

I used these vids to help build "T" gauge.  They are not perfect, but help for "visual" learners.  Parts 1 and 2.

Click Here (www.youtube.com)

http://www.youtube.com/watch?v=lhSp1_x5CLw

A video showing the typical vibration/oscillation of the gauge.  The video also is about changing the Vib pump pressure, but another topic.

http://www.youtube.com/watch?v=joQs13t15QI

Oil filled on Silvia

http://www.youtube.com/watch?v=hfqkprLNQIY

 
D4F also at
http://www.gaggiausersgroup.com/
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DaninMaryland
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Joined: 3 Jan 2013
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Posted Wed Jan 23, 2013, 5:12pm
Subject: Re: $10 portafilter brew pressure gauge
 

i put together the portafilter gauge as the OP did tonight for my silvia.  ended up being $14, $10 for the 300 psi gauge, and $4 for the fitting.  i got a air filled gauge not oil, works fine with no jumping around.  i really dont think you need to worry about getting a glycerin/oil filled gauge for this application.  if i was putting a permanent gauge on the machine, absolutely you don't go with a dry gauge.  but for something you are only going to use a few times a year to check your pressure, save the money and get a dry gauge.  no issues for the Silvia.  Thanks OP.
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RapidCoffee
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RapidCoffee
Joined: 4 Dec 2004
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Posted Wed Jan 23, 2013, 5:47pm
Subject: Re: $10 portafilter brew pressure gauge
 

After seven years and three espresso machines, my original air-filled gauge is still working fine. :-) I will gladly concede that an oil- or glycerin-filled gauge would be preferable, but neither was available in the hardware store where I purchased the gauge.

If you prefer a commercial product, you have several options (such as this or this). I fail to see any significant difference from a home-built gauge (other than price), but perhaps I'm missing something.
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D4F
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Joined: 15 Mar 2012
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Posted Wed Jan 23, 2013, 9:12pm
Subject: Re: $10 portafilter brew pressure gauge
 

Mine is not oil filled nor was I advocating that, I was explaining why the gauge needle oscillates.  I would probably used oil filled if I was mounting one for ongoing use, but as explained, it damps the needle, not really changing the basic function.

 
D4F also at
http://www.gaggiausersgroup.com/
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sleepdance
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sleepdance
Joined: 27 Feb 2007
Posts: 98
Location: USA
Expertise: I love coffee

Espresso: Faema C85
Grinder: La Pavoni Zip
Vac Pot: Yama
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Roaster: Behmor
Posted Wed Jan 23, 2013, 10:55pm
Subject: Re: $10 portafilter brew pressure gauge
 

DaninMaryland Said:

i put together the portafilter gauge as the OP did tonight for my silvia.  ended up being $14, $10 for the 300 psi gauge, and $4 for the fitting.  i got a air filled gauge not oil, works fine with no jumping around.

Posted January 23, 2013 link

Was there anything you did that kept it from jumping? The dry gauge goes crazy on my machine.
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DaninMaryland
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Joined: 3 Jan 2013
Posts: 79
Location: US
Expertise: I love coffee

Espresso: V2 Silvia
Grinder: Vario-W
Posted Thu Jan 24, 2013, 5:37am
Subject: Re: $10 portafilter brew pressure gauge
 

sleepdance Said:

Was there anything you did that kept it from jumping? The dry gauge goes crazy on my machine.

Posted January 23, 2013 link

Mine doesnt jump at all, the pressure ramps up steadily and tops out and stays there.  no variations
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RapidCoffee
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RapidCoffee
Joined: 4 Dec 2004
Posts: 1,933
Location: Rapid City, SD
Expertise: I love coffee

Espresso: La Spaziale S1
Grinder: Mazzer Robur
Vac Pot: Yama
Drip: misc
Posted Thu Jan 24, 2013, 6:39am
Subject: Re: $10 portafilter brew pressure gauge
 

sleepdance Said:

Was there anything you did that kept it from jumping? The dry gauge goes crazy on my machine.

Posted January 23, 2013 link

It could be the particular gauge you are using, or something in your machine. I've had no trouble measuring the brew pressure on rotary pump espresso machines (Rancilio L7, QM Vetrano, Spaz S1), so it could be the vibe pump. But Dan and others have reported good results on vibe pump machines, and commercial PF gauges appear to be pretty much identical in design.
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