# DIY Portafilter Pressure Gauge



## winz (Oct 10, 2019)

Hey guys!

i just build myself a pressure gauge for my new Gaggia Classic Pro 2019

quick question, I followed some design and there's an outlet. I have the double filter inserted into the portafilter. When I turn on the outlet of the pressure gauge (red lever), I can't seem to get any pressure whilst I see others getting an accurate pressure reading with the outlet turned on.

When I turned off the outlet, the pressure builds to 15Bar and starts to leak all over the group head.

any suggestions on how I can use it?


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## ArisP (Dec 17, 2019)

Isn't the "outlet" just a valve that allows water to escape?

Assuming that it's built correctly, I do seem to recall that the Classic is set for 15bar, since it is meant to work with a pressurized pf.


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## Jollybean (May 19, 2013)

I think the idea is that you adjust the tap to simulate the flow you would get through a puck. Consensus appears to be that 10 bar static (i.e. with the tap closed) equates to about 9 bar when flowing. So on mine I didn't have the tap and just set it to 10 bar


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## cracked_bean (Apr 13, 2014)

Just from a fluid flow point of view you are just measuring the pressure drop from atmosphere to the sensor with that tap open. If you put 1 bar resistance on the tap you would measure 1 bar.

Sent from my iPhone using Tapatalk


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## winz (Oct 10, 2019)

Jollybean said:


> I think the idea is that you adjust the tap to simulate the flow you would get through a puck. Consensus appears to be that 10 bar static (i.e. with the tap closed) equates to about 9 bar when flowing. So on mine I didn't have the tap and just set it to 10 bar


 Hi! How do you know how much to open or close the tap to simulate the flow?


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## cracked_bean (Apr 13, 2014)

You are doing all this to set the max pressure such that you get 9 bar through the puck. There is a difference between a static and a dynamic pressure, such that the total pressure of the dynamic system takes into account fluid flow as well. If the flow is stationary the static pressure becomes the total pressure. Jollybean has said that you are looking for about 10 bar with the tap fully closed to achieve the 9 bar pressure drop, so do that. Close the tap and adjust until you only get 10.

The issue here is that to properly simulate a puck you would need a way to measure the "closeness" of your tap out of the system, then place it in the system to calibrate, ultimately this doesn't really sound feasible.


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## DavecUK (Aug 6, 2013)

First remove the double basket as you can't get a proper seal with that in place, under any pressure water will pour out all round the group!

Below a couple of old articles to read

http://coffeetime.wikidot.com/pressure-measuring-portafilters

http://coffeetime.wikidot.com/pressure-measuring-portafilter-rising-pressure

The pressure you want to set is the max static pressure preferably ignoring the later rise caused by water expansion on heating (It usually jumps to as value, then continues a gradual rise, that's the expansion). Usually best done by disconnecting a heating element. The dynamic pressure really doesn't tell you very much as it can depend on other factors.


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## Jollybean (May 19, 2013)

Hi Winz. Dave really does know what he is talking about so I would follow his advice above and just do static pressure at 10 bar with the tap closed, rather than worry about dynamic pressure ?


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