Mini Grimac pumps slowly - scale problem?

[rfc]

Total newbie here. Inherited from the local restaurant a MiniGrimac (now called the Uno, I think) which stopped working even after $350 worth of work (new seals, new solenoids etc.).

I took it completely apart and emptied about 2 lbs of mineral deposits from the innards and re-assembled. Appears to work as designed: (brew temp 203 degrees after flush, pressure capable to 12 bar, etc). The only thing that seems a little weird is that it takes an extraordinary amount of time to flush, and it only pumps about 1-1/2oz in a full minute with no portafilter on. This seems a little low to me.

I started with "French Roast" ground at the local supermarket set to "espresso" grind. Like powder.

If I use anything like 30 lbs of pressure, it takes 30-45 seconds before any liquid even comes out. I know I can tamp with less force, but would like to at least approach the "golden rule" numbers before I proceed with the learning. Everything that has come out of the thing so far has been very bitter.

So the question is: In order to minimize variables, can anyone recommend a good "starter" coffee, preferably bought from the internet (unless someone here wants to sell me a pound or two) to test with. How do I specify the grind? I know eventually if not sooner I will need to buy a grinder but right now I just want a good cup of joe.

[HB]

The only thing that seems a little weird is that it takes an extraordinary amount of time to flush, and it only pumps about 1-1/2oz in a full minute with no portafilter on. This seems a little low to me.

Something is not right. Either the pump is not working correctly, or the HX is so full of scale that it's obstructed. Below is the flow rate charts for a Ulka vibration pump:


Performance charts from www.ulka.it

The unobstructed flow rate is about 650ml. The expected flow rate should be somewhat less since there is a gicleur valve restricting the flow even when the portafilter is removed. As a quick check, try removing the "mushroom" and checking for scale buildup:



It's a safe bet that if you saw scale on the boiler, it's worse in the HX. That turned out to be Geoff's problem as described in Sputtering e61 & HX scale build-up - Cured! Sorry, but I suspect that changing coffees will not help at all.

PS: Once you have the pump flow issue resolved, check out The Home Barista's Guide to Espresso, especially the section on technique. It covers a lot of ground from newbie to advanced.

[malachi]

I fear that the coffee you use is going to not fix the trouble you're having. You really are going to have to invest in a grinder. The odds of getting the correct grind when buying pre-ground coffee are similar to the odds of success at pin-the-tail-on-the-donkey played blindfolded in the dark in a hailstorm where the donkey is somewhere within a half mile of you.

[rfc]

Something is not right. Either the pump is not working correctly, or the HX is so full of scale that it's obstructed. Below is the flow rate charts for a Ulka vibration pump:

OK. Thanks for the facts. When I first got the machine, my cleanout included the "mushroom", which did indeed have a ton of crud--not scale, per se, (like calcium), but hard minerals.

I cleaned that all out and got reasonable flow (but not the levels in the chart). But before that, I pumped vinegar through the unit for several hours to descale any calcium buildup.

I suspect that from all my opening, cleaning, shaking and scrubbing, there is still stuff floating around in the system.

I do note now, that when I turn on the pump, very little flow is apparent but water is coming out the silicone drain pipe into the tray. That comes from the main brass "block" thing, which also seems to feed the HX with water.

I'm betting I still have sludge in there perhaps.

[HB]

I do note now, that when I turn on the pump, very little flow is apparent but water is coming out the silicone drain pipe into the tray. That comes from the main brass "block" thing, which also seems to feed the HX with water.

That's your expansion valve / OPV runoff tubing. If any water comes out of that when the portafilter with blind basket is not in place, that indicates complete blockage. See brew pressure adjustment for a detailed explanation. My guess is that the gicleur valve is blocked.

[barry]

the passageways in the group might be occluded with scale and require serious descaling efforts (more than just a flush).

solenoid valves also scale up and restrict flow.


--barry "more to descaling than just the boiler"

[rfc]

If the gicleur valve is the little pinhole device at the top of the "mushroom", then it's clear. I think the problem may be upstream more. I removed the Head Group Screw that blocks the drill hole made in the Head Group and no water comes out there either.

Tonight I'll track it from both ends (Group Head and Pump) and see where the flow stops. It either has to be in the OPV (now that I know that's what the brass block thing is) or the injector in the boiler. I know the thermosyphon tubes are clear as a bell now, so it's not them.

[barry]

Tonight I'll track it from both ends (Group Head and Pump) and see where the flow stops. It either has to be in the OPV (now that I know that's what the brass block thing is) or the injector in the boiler. I know the thermosyphon tubes are clear as a bell now, so it's not them.

both of those can scale up, and so can the holes where the thermosyphon tubes connect to the group. and, again, the passageways in the group itself can plug up. also, check valves can stick closed.

[rfc]

Tonight I'll track it from both ends (Group Head and Pump) and see where the flow stops. It either has to be in the OPV (now that I know that's what the brass block thing is) or the injector in the boiler. I know the thermosyphon tubes are clear as a bell now, so it's not them.

both of those can scale up, and so can the holes where the thermosyphon tubes connect to the group. and, again, the passageways in the group itself can plug up. also, check valves can stick closed.

I'm onto it now (I think). I have pressure all the way to the group head and I have already dis-assembled and reassembled the mushroom. I think I am down to between the orifice in the top of the mushroom (the gicleur valve?) and the holes that lead to the filter screen itself.

What does the "infusion cap" on the right side of the unit do? Just seems to be a big chamber in there?

Can the round brass thing in the center of the portafilter gasket be unscrewed without a set of snap ring spanner wrenches? I'm pretty sure that the hole beneath the group head screw is clear, which really only leaves the hole from there down to the portafilter.

Finally, I have ruled out the pressure dump solenoid, because it dumps properly when you flip the switch off.

I'm not looking to be held by the hand here, but if anyone can shed some technical light, it is much appreciated.

[HB]

On my machine there's four small holes that connect the outside chamber of the mushroom (where water circulates) and the small upper chamber containing the gicleur / screen capped by the big nut on the top of the group. If you've already checked they are clear and the gicleur is clear, then the next stop would be the water jet breaker:



It's facing downward in the picture, but there's a center slot on my jet breaker (looks like a big screwhead). A fat stubby screwdriver does the trick. Maybe there's oodles of gunk behind it. I've never seen anything like it, but I've heard plenty of horror stories and seen graphic photos of scale buildup online. It's not pretty.

PS: I am assuming yours is a solenoid-type pressure release; if so, then that big nut on the side of the group only caps off the hole where the lever would go.

Side-by-side comparison of solenoid-type (Valentina) and E61 lever (Levetta)

[rfc]

Thanks. I am suspecting the water jet breaker. After 10 or 15 seconds, I get paltry amounts out of those four holes, and sometimes it only comes out of one or two. It should be gushing.

I just need to figure out a way to make a spanner wrench. Mine does not have a slot. It's four 1/8 (approx) holes on about an 1-1/2" center. It's probably a special tool that fits up there and unscrews it.

The only bothersome part is that with the cover to the "infusion device cap" off, I don't get much water out of there either. I'm getting close. I want to smell the coffee!

[HB]

Does your water jet breaker look like this (rightmost)?

If so, I need to read more carefully next time. That's the stock water jet breaker / pod adapter for my machine, La Valentina. While it's really helpful to have the special tool you mentioned, I coaxed mine out by gently tapping a cutoff nail inserted in one of the holes. Later I replaced it with the standard E61 dispersion screen.

PS: If you removed the big bolt on the side of the group capping off chamber 14 and water didn't gush out, you need to look higher.


E61 patent diagram - modern versions are almost identical

[rfc]

In the meantime....I applied a fine wire to the four holes and also used some compressed air to shake things up and now get a nice flow--probably in the neighborhood of 1.5 cc/sec at zero pressure.

I'll call this patient "stable" and won't let 'er out of the ICU until I can completely disassemble the group head, but will call this a success.

Threw some coffee in the portafilter and for the first time ever, pulled a double with blonding right at 30 seconds. Not much for taste, because the grind was not fresh, but I am on my way to the hard part now....learning how to do this (make coffee that is).

Thanks for all the help and ideas.

[rfc]

HB, thanks for the tip about the nail. I should have been able to figure that out. I used a center punch and got the water jet breaker (which looks like the big one in your picture) off and there was a lot of nasty stuff in there. Not so much like the sand I found elsewhere in the machine, but just "coffee sludge".

I think now that the entire water path has been cleaned, I need to focus on getting all the old coffee stuff off the grouphead.

Thanks again.

[HB]

Good to hear you're up and running. By the way, if you haven't done so already, check out the Buyer's Guide to La Valentina. It's got a lot in common with your machine.

For future reference, I retitled this thread to match the actual topic. Returning to your original question, the thread roasters poll nominations is a good place for coffee recommendations.