No flow during first warming flush

[db01]

Hi Mini owners,

Please put my mind to rest or sound the alarm if something seems out of the ordinary with what I see with my mini II, as described below. I bought my machine new and it is now about two months old.

I have the single cup button programmed to deliver 2oz without a pf and I use this for warming flushes. The first flush of the day would not deliver any water out of the group, although I can hear the pump working. After about ten seconds the pump stops automatically as if the flow meter sensed 2oz being dispensed and the temperature lights go out as normal. During the second flush, water would start to come out of the group and I would get anything from 1 to just under 2 oz.

Subsequent activation of the pump would deliver water out of the grouphead immediately, until I let it sit idle for an hour or two.

If above behavior is not normal, I can eliminated the following culprits:
1) I do not have a water filter installed in the reservoir that can block flow and there is no hose attached to the outlet on the inside of the reservoir.
2) I drop the screens/dispersion block every week (I only do 10-15 shots per week) and soak it in Cafiza. I also run blank shots and wipe the screens after every shot and I checked that the holes are not clogged.

I read somewhere that some machines need to fill up their water pathways when the pump is first activated after an idle period. Is this what I am seeing? It is hard to imagine that 2oz of water is somehow "disappearing" from the waterways in my Mini overnight.

I have measured the flow rate of my pump (through the group without pf) once water is flowing freely. A few days ago I got ~350 ml/min, yesterday I got 450 ml/min and today I measured 410 ml/min. There's a post on this forum that suggested the flow should be around 550 ml/min for the Mini's vibe pump, but I guess it could vary from pump to pump? (And apparently from day to day with the same pump!? Although I would be the first to admit I am not running a well controlled experiment.)

I don't know if it is related, but I get a dwell time of 8-12 seconds when pulling shots (no preinfusion chamber). Is this on par with other mini owner's experience or could it be related to the "low flow" of my machine? Once flow starts, shots pull OK although the volume ends up short in my opinion - I get 40-45ml in 35 seconds from 15g of coffee at 50% brew ratio (could be the specific blend, which I only use in a 4-8 day post-roast window). For now I am not worrying about the shot volume as long as it taste OK - I manage to *sometimes* get close to the flavours that my local cafe gets using the same beans.

I appreciate any input, thanks all.
- DB

[goodboyr]

I've had issues with the flow sensor. It could cause this type of problem. The original sensors have been modified I understand to deal with low flow. When mine was replaced the flow went up substantially. And if the temp sensor starts wandering you could start the machine after idle with a boiling shot which would show very little flow.

[chas]

There is a check valve at the outlet of the tank to prevent water from flowing back into the tank. If it failed and water drains out between the pump and the tank after an idle period, something this might happen. That said, such a problem has never been reported on this forum. However, after close to 10 years of running this forum I have seem a lot of people eventually see problems that no one has seen before.

[db01]

Thanks Bob and Chas for chipping in, I appreciate your input.

I've had issues with the flow sensor. It could cause this type of problem. The original sensors have been modified I understand to deal with low flow. When mine was replaced the flow went up substantially.

I am hoping it is not the flow sensor, given that this machine was manufactured in 2013 and is only 2 months old, it should have the latest and greatest. I will leave investigating the flow sensor as a plan B.

And if the temp sensor starts wandering you could start the machine after idle with a boiling shot which would show very little flow.

I have measured the temperature at the group with a DIY-type thermocouple solution over the last hour in 15 minute intervals and it seems pretty consistent. I also never see sputtering or hear hissing when pulling warming shots, so I think I can rule this one out.

There is a check valve at the outlet of the tank to prevent water from flowing back into the tank. If it failed and water drains out between the pump and the tank after an idle period, something this might happen.

I think you are on to something. At times when I remove the tank water would flow freely from the outlet of the tank and spill all over the counter and floor. I am going to run a test where I wipe the tank dry and let it sit overnight - if there is about 2 ounces of water in the tank the next morning, I have found the culprit.

That said, such a problem has never been reported on this forum. However, after close to 10 years of running this forum I have seem a lot of people eventually see problems that no one has seen before.

I think I have gone over just about every post on this forum and can confirm that this has not been reported before. Hopefully it can be fully documented here, including a solution. Thanks again for the pointers so far

[chas]

I got lazy in my last post. I was going to end with a recommendation that you do just such a test as you have outlined.

In the parts manual this is called (in Italian) "valvo non returno". It looks pretty simple and probably easy to take apart and troubleshoot. There appears to be a spring a plunger and a couple of "O" rings. It's very possible that one of the "O" rings is pinched, missing, broken, or otherwise misaligned internally.

It looks like you need to unscrew parts 7408 and 7409 and then inspect 279, 586, and 7406. I assume that in the rest state a spring should hold this valve closed with the "O" rings sealing the connection. Then when the pump kicks in it creates a partial vacuum that opens the valve.

valvononreturno.gif (16.68 KiB) Viewed 18761 times

[db01]

My tests did not produce the results I was hoping for - no water in the tank the next morning and still nothing out of the grouphead during the first few seconds .

I am not yet ready to rule out the "valvo non returno", though. I am going to take it apart as soon as possible (I am travelling for work at the moment).

[GDK]

Have a look at this thread:

http://www.s1cafe.com/viewtopic.php?f=5 ... 284#p18284

If the tank is not seated well (i.e. not firmly pushed to the back), it is possible that some air gets in and that may cause the delay of water flow. This could for example happen when the pump starts as it may sucks some air in. Just a thought - sometimes it is the simple things that cause problems.

[db01]

So I finally had a chance to take a look at the internals of the "non return valve" at the tank outlet. The compression coil spring responsible for sealing the valve is completely rusted up and disintegrates at the touch. That after two months Here is a photo:

Broken spring in tank non-return valve

non-return valve small.jpg (13.04 KiB) Viewed 18651 times

I am currently in touch with my supplier to see if I can find a replacement. I am also scavenging every printer and toy that I come across in the hope that I find a spring that matches

In the meantime I am just living with the issue, which is mostly an annoyance when refilling the tank. Hopefully I am not causing damage to other parts in the machine...

[chas]

I vaguely remember reading about some piece part in that general vicinity of the Mini that was rusting out within months of purchase, but I never knew exactly which piece they were talking about. Maybe this is it. It sounded like a batch of these valves were made using a standard steel springs rather than ones made of stainless steel or some other non-rusting/corroding metal.

Any any rate it ought to be a free replacement. Do you know if your supplier is going to just send a new spring or replace the entire valve? I guess it mostly depends on how they purchase/stock spare parts.

[chas]

db01, I sent you a PM with more info on the spring situation....

I did that because the e-mail attached to the PM is not really worded for public consumption and I wanted you to see it as it was sent rather than editing it. Based on when you received your Mini you must have gotten one of the last ones before they started swapping out all those springs for stainless.

The bottom line is that anyone buying a new machine now will get one with all stainless steel springs.

When you get the replacement spring, if it was not shipped directly from Chris Coffee, you might want to be sure it is one of the new stainless ones Chris is providing and NOT a spring from LaSpaziale. Just use a magnet. If a magnet will not pick up the spring, you have the correct stainless replacement.

[db01]

A quick update: I installed a new stainless steel spring this week and my machine is back to normal - problem solved!

Thanks Chas for putting me on the right track.

I live in South Africa and bought my Mini from a local distributor. He was willing to replace the spring, but would have used the exact same version from La Spaziale as the one that failed, so I eventually "imported" a proper stainless steel alternative from Chris' Coffee Service.

Cheers
DB

[chas]

glad to hear it. thanks for the feedback.