Pressure pump gauge going crazy

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Yerushalmi
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Real Name: Yaakov Asher Sinclair
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Postby Yerushalmi » Sep 19, 2010, 3:57 pm

When the pump on my Brasilia Mini Classic kicks in, the machine doesn't go silent like it used to (before it was repaired) now it makes almost the same noise as during the pre-infusion stage, and the gauge oscillates very fast
see here:



any ideas?
thanks!

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HB
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Postby HB » Sep 19, 2010, 4:10 pm

My guess is that the dampening coil is filled with water. From Building a Portafilter Pressure Gauge:

HB wrote:Allow me to clarify... they're called vibratory pumps for a reason:

Image
Image courtesy of Made in the GARAGE

How much of the 60Hz back-n-forth is reflected in the gauge depends on the machine. For example, if it has a gicleur (orifice) in the grouphead, the gauge will vibrate significantly less. The sensitivity of the gauge itself also comes into play. To dampen needle flutter, manufacturers use a coil of thin copper tubing or snubber (e.g., an inline porous stone or dampening piston).

As an example, the needle on the portafilter pressure gauge I made from Ace Hardware parts vibrated like a hummingbird's wings when used on my Rancilio Silvia. It buzzed on La Valentina (E61 with gicleur), but was readable. Of course the Scace II has a quality liquid-filled gauge and its reading is rock solid.

Rotary pumps also generate pulses, but they're barely noticeable for most air gauges with no dampening.

That is, to avoid needle flutter, espresso machines need some dampening agent between the pump and the gauge if the gauge is air filled (instead of oil /glycerin filled). The gauge in the video is clearly an air gauge.
Dan Kehn

Yerushalmi
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Joined: Sep 10, 2008, 7:43 pm
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Postby Yerushalmi » Sep 19, 2010, 4:17 pm

Is this something I can/ought to fix by myself?
thanks

Yerushalmi
Posts: 31
Joined: Sep 10, 2008, 7:43 pm
Real Name: Yaakov Asher Sinclair
Equipment: Pavoni Peacock, i-mini grinder, handpresso
Location: Jerusalem

Postby Yerushalmi » Sep 19, 2010, 4:18 pm

btw
Is the Brasilia a rotary pump machine or vibe?
thanks!

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HB
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Location: Cary, NC
Interests: Happy family, exceptional espresso, fast cars.

Postby HB » Sep 19, 2010, 4:29 pm

Judging from the sound on the video, your machine unquestionably has a vibratory pump. I recommend you take it to a qualified repair technician since it may be necessary to replace the gauge and/or solder in a new dampening coil; that's beyond the skills of a casual DIYer.
Dan Kehn

Yerushalmi
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Joined: Sep 10, 2008, 7:43 pm
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Postby Yerushalmi » Sep 19, 2010, 4:41 pm

Dan
If I just leave it as it is, will it damage the machine? It's a big shlep to the repairman (two hour drive!)
thanks

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HB
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Real Name: Dan Kehn
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Location: Cary, NC
Interests: Happy family, exceptional espresso, fast cars.

Postby HB » Sep 19, 2010, 4:50 pm

Other than the loss of a steady brew pressure reading, there is absolutely no harm to leaving it as-is.
Dan Kehn

truly great coffee roasted to highlight its inherent quality
jasonmolinari
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Postby jasonmolinari » Sep 19, 2010, 7:10 pm

My Isomac Tea exhibited a similar pressure gauge flutter.
I took the gauge and connected dampening tube off and applied heat to the tubing carefully with a blow torch. Water sputtered out the end of it. Did that until it seemed dry.
that fixed the problem...

Careful not to get too close to the gauge with the torch!