Olympia Cremina has spongy pull after servicing piston seals

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thesharpener
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Postby thesharpener » Apr 17, 2017, 5:17 pm

I'm hoping to get some advice troubleshooting a spongy pull on my Cremina. My understanding from digging around on HB.com is that the spongy feel is the piston compressing air above the prepared basket.

I recently removed the piston and cleaned and lubricated all the seals. Prior to performing this upkeep, there was no sponginess in the pulls.

My typical process is a 14.5g coffee dose, lock portafilter, raise lever, preinfuse for 10-15 seconds until droplets are forming on the basket, pull and release after 25-30 g espresso are in the cup. My boiler pressure cycles from 11.5-14.5 psi (0.8-0.9 bar). I haven't weighed a shot since servicing the piston seals, but I have noticed that visually there seems to be less volume in the cup.

Since I didn't experience spongy pulls prior to the maintenance, is there potential that the piston cup seals are not installed correctly, or possibly need to be replaced? Last time I serviced the seals, I didn't encounter any sponginess afterward.

Any insight is appreciated.
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dominico
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Postby dominico » Apr 18, 2017, 1:24 am

I "could" be that your old seals allowed for a small steam leak, helping your boiler purge itself of trapped air. Your new seals now seal better, meaning you could have trapped air in your system which is impeding a proper preinfusion. You can test this by bleeding out steam from the steam wand while doing a couple half-pumps with the lever before a shot.
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thesharpener
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Postby thesharpener » Apr 18, 2017, 11:18 am

Update: last night I disassembled the group to verify all the seals were seated properly and installed in the correct orientation and everything looked fine. I reassembled the group and the pulls were still spongy. I also noticed after a pull there are quite a lot of coffee grounds on the dispersion screen which never happened before.

To clarify, the piston seals aren't new, but I did remove, clean and lubricate them before reinstalling.

You can test this by bleeding out steam from the steam wand while doing a couple half-pumps with the lever before a shot.


I'll give this a try today after work and see if it helps.
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drgary
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Postby drgary » Apr 19, 2017, 1:32 am

You can also grind a touch coarser or downdose and preinfuse long enough so drips come into the cup. If you're using a bottomless portafilter the drips should start to distribute themselves evenly, then slow down. This ensures that the coffee cake is thoroughly infused with water and all the air has been driven out. Half pumps as described above also help infuse the coffee cake and drive out air.
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thesharpener
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Postby thesharpener » Apr 19, 2017, 12:35 pm

Post by drgary » Yesterday, 10:32 pm

You can also grind a touch coarser or downdose and preinfuse long enough so drips come into the cup. If you're using a bottomless portafilter the drips should start to distribute themselves evenly, then slow down. This ensures that the coffee cake is thoroughly infused with water and all the air has been driven out. Half pumps as described above also help infuse the coffee cake and drive out air.


Tried domico's half pump with the steam tap open suggestion, but no luck. Also tried your advice to adjust dose and grind, but also no luck.

There is a vigorous gurgling when the water enters the group, and some hissing too. There appears to be channeling in the same spot each pull, but I know my distribution/tamp is decent since my pulls were good prior to servicing the piston seals (aside from a few spritzers as my HG-1 burrs break in). The coffee puck looks wet and violently disturbed on top, and there is quite a bit of ground coffee on the dispersion screen. Prior to the group maintenance, the coffee puck was tight and dry, and the dispersion screen was always clean as a whistle. Worst part is, the espresso tastes vile...I could deal with a spongy pull and dirty screen if the drink was good.

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I decided to remove the group, disassemble and inspect (again). This time I found the upper piston rod seal was damaged, so maybe this is the culprit, however there are no signs that the damage has resulted in a bad seal between the group and piston rod. I have a new one on the way from Cerini's so we'll see.

Image

A wild guess of a theory...is it possible that water being sucked in from the boiler could flash boil as it enters the group, if the pressure gauge I use to set the p-stat is wildly out of calibration? Per my pressure gauge my boiler is cycling between 0.8-0.9 bar, but if the gauge is off, who knows.
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drgary
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Postby drgary » Apr 19, 2017, 12:52 pm

I doubt that seal is the culprit. If anything, it would release pressure that's too high. It would be interesting to see a short video of water coming from the shower screen when you raise the piston. Also, if you have a way of measuring pressure with a different gauge or measuring water temperature just at the top of the coffee cake, that would give more feedback.
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thesharpener
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Postby thesharpener » Apr 19, 2017, 2:24 pm

Yeah, I doubt it is the seal either, but I'm stumped and a replacement is only $15 plus shipping. I'll make short video of the flow from the screen tonight.

I'm planning to pick up a replacement pressure gauge to check boiler pressure. I did notice this morning that with the current gauge I'm using (http://www.valworx.com/product/stainless-steel-pressure-gauge-25-30-psi), when the gauge is pegged at zero, there is still quite a bit of steam left in the system, so I'm hopeful this may give some answers.
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Postby drgary » Apr 19, 2017, 2:51 pm

It could be time for a white vinegar/water descale. Sometimes pressurestats start getting clogged and don't shut off soon enough.
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max
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Postby max » Apr 19, 2017, 3:20 pm

If it's always in the same spot, it seems like an extreme case of what's described in here: Olympia Cremina's coffee puck has a dent after replacing the seal?!


The consensus, if there was any, was that it was there caused by the seal. I have had the same issue (as in that thread) on at least two Pavonis. They do have the same seals, so I recently tried to change to another manufacturer, and although it is not entirely gone, I believe there is a difference.

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thesharpener
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Postby thesharpener » Apr 19, 2017, 3:58 pm

It could be time for a white vinegar/water descale. Sometimes pressurestats start getting clogged and don't shut off soon enough.


Good idea, I recently descaled the boiler after discovering there is more hardness from my tap water than I assumed (using the aquarium test kit recommended on HB.com). I use 70/30 formulated water now so boiler scale shouldn't be an issue, but I did not descale the p-stat or p-stat pipe. I should also mention the original p-stat that came with the machine was badly damaged, so I have the Ma-ter replacement from Cerini's installed, and I have heard these are not as reliable as the OEM p-stat.

If it's always in the same spot, it seems like an extreme case of what's described in here: Olympia Cremina's coffee puck has a dent after replacing the seal?!


This is a really interesting possibility. I will read this thread in its entirety on my commute home from work.
Pete - LMWDP #572