# Occasional brew pressure fluctuations problem...



## MrShades (Jul 29, 2009)

I've got a small problem with my Alex Duetto, in that occasionally the brew pressure seems to drop (or not rise) and fluctuate. I'll try to explain:

- Normally (and especially when the water tank is full/almost full) the machine preinfuses with the manometer at 8-9 bar happily and then it increases to hold at 10bar brew pressure and works faultlessly throughout a pour, staying on 10bar solidly.

- Occasionally (and I've noticed that it does tend to happen when the tank is less full) the machine starts at 8-9 bar and then whilst in the pour the pressure raises slightly (perhaps half a bar) and then drops again, raises then drops, raises then drops, constantly fluctuating between 8-9 bar - with the pump making a less happy sound (as if there is air in the water feed pipe) and it never hitting the normal, solid 10bar point.

When this happens I can normally fill the tank right up and sometimes back-flush with a blind filter and it normally goes away for a while. No idea what's causing it though, and I'd like to resolve it.

I guess it could be the OPV or the pump - but not sure what's going on and would really appreciate anyone that knows what they're talking about offering any advice.

Many thanks,

Shades


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## glevum (Apr 4, 2013)

is it like this


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## MrShades (Jul 29, 2009)

Similar, but not really - mine really is very regular and minor (0.5 bar max) fluctuations above 8 bar... though I guess a video would make it much easier to see (and hear) what happens. Crucially, much like that video, when it has this problem it's not hitting a normal 10bar brew pressure at all (though can do on the next pull)

I'll try and video it next time it happens and post back on here then.


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## Monkey_Devil (Jul 11, 2011)

I had bad fluctuations in my brew pressure on brewtus. I replaced the pump and OPV at the same time because I wanted to upgrade the OPV. It fixed the problem - I'd guess it was the pump.


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## El carajillo (Mar 16, 2013)

I have read somewhere that rotary pumps are not happy running from tank supply and may need a"flowjet" to help overcome problem ?


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## MrShades (Jul 29, 2009)

OK - I've captured a couple of brief video clips - all of which are with a blind filter in the machine:

The first one shows the problem:






You can tell that the first time it still struggles, but a few hisses and things later it settles, the pump sounds more normal and on the 2nd pull it hits 10bar on the manometer perfectly OK - as it should do.

At this point I pulled a double espresso and it all worked fine.

It seems that if I leave the machine for a while, hot, then the problem starts again - and often pulling a few "cooling" shots helps it to settle down to normal again.

All very odd... but I'm guessing that it's a valve sticking somewhere. My current guess would be to take the case off and have a good look and clean of the anti-backflow / non-return valve - wherever and whatever it is... and see if that helps. Certainly it seems like a similar problem to this one for an Izzo Alex (HX) on Coffeetime wiki: http://coffeetime.wikidot.com/izzo-alex-anti-backflow-also-called-non-return-valve

Anyway - all help or advice, or just thoughts would be very much appreciated.

Shades


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## El carajillo (Mar 16, 2013)

I have read in a coupe of articles that rotary pumps are not happy being tank fed due to lack of pressure as they are intended to "push" water rather than pull and push.

I believe that because of this and the increasing use of them inPro/sumer M/ch they have been improved /modified to overcome this problem.


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## repeat (Nov 14, 2009)

Have you given it a descale to see if that clears the problem?


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## MrShades (Jul 29, 2009)

Well, it was reasonably recently descaled - but I think I may try a good strong citric acid descale and see if that helps at all.


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## garydyke1 (Mar 9, 2011)

After I descaled Brewtus I had a couple of days with a similar issue, I suspect a flake got stuck somewhere and eventually dislodged as the issue hasnt returned


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## MrShades (Jul 29, 2009)

A nice strong citrus acid solution is sitting in it as I type.... will give it a good descale and see what happens. I suspect that it's the anti-backflow valve sticking open due to scale or similar and the alternative was to start taking covers off and pipes apart - so hopefully this will do the trick. Will report back once completed.

Thanks for the feedback / assistance - it's appreciated.


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## repeat (Nov 14, 2009)

Hopefully it worked.


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## MrShades (Jul 29, 2009)

Well, a good strong citric acid descale with a hot solution (as I was trying to make sure that the pre-boiler water path was properly descaled, I went strong and 60c hot!) seems to have made a difference.

This morning, when I would usually have had to 'flush' water through in order to avoid the pressure fluctuation - it worked flawlessly. Time will tell but it seems to have done the trick.

Last time I descaled I used a comparatively weaker solution that was cold - which was probably quite effective at descaling the 'hot' parts of the water path but less so on the tank-to-boiler components.

Anyway, consider it solved unless I post otherwise on here in the next few days.

Thanks all!

Shades


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## glevum (Apr 4, 2013)

MrShades said:


> Well, a good strong citric acid descale with a hot solution (as I was trying to make sure that the pre-boiler water path was properly descaled, I went strong and 60c hot!) seems to have made a difference.
> 
> This morning, when I would usually have had to 'flush' water through in order to avoid the pressure fluctuation - it worked flawlessly. Time will tell but it seems to have done the trick.
> 
> ...


Well done. I have definatly made a note of this case it happens to me.


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## specialpants (Jun 25, 2013)

This happened to me just before I left Australia too (





)

I never got around to resolving it. I first tried descaling (which fixed it for about 2 weeks) then it came back. I tried playing around with it (ie raising the pressure beyond 13 bar) to see if it was the OPV. When I did this, the OPV started squeaking (metal on metal) so I replaced it to see if would help.

My gut feel is that it's the actual pump (not motor) that's causing it to do it. The machine's in storage for the time being, and I'll fix it up when I return to Australia in about 1.5 years.

Anyways, keep us posted with how you go.


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## MrShades (Jul 29, 2009)

It's been fine since - though when I descale now I tend to leave it overnight to make sure it's done properly - so scale is the only thing I can put it down to.

Good (in a way) to know that I'm not the only one that's suffered from it.


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## DavecUK (Aug 6, 2013)

MrShades said:


> It's been fine since - though when I descale now I tend to leave it overnight to make sure it's done properly - so scale is the only thing I can put it down to.
> 
> Good (in a way) to know that I'm not the only one that's suffered from it.


Nooooo!!!, not overnight, please no.


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## MrShades (Jul 29, 2009)

Is it really THAT bad Dave? What's it going to damage?


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## DavecUK (Aug 6, 2013)

MrShades said:


> Is it really THAT bad Dave? What's it going to damage?


Each descale it a little death for your machine....ideally you should be using water that means you don't need to descale and water with little dry solids or other stuff in it to leave deposits on things. Descaling also strips oils from the group components, so you must lube each time you descale it's a good idea to actually diassemble the group and lube after a descale, because the upper group valve can become VERY hard to move and result in premature pin wear. Plus your leaving descaler in the rotary pump chamber overnight, which is asking for trouble. your comment about a good strong descale solution is especially worrying if it was stronger than that suggested in the userguide.

I am also not convinced there was necessarily a lot wrong with your machine, but couldn't see the PID or know what the temperature of the water was in the tank when it was sitting, do you leave the steam boiler on a lot etc..or even if the backflush handle was weeping even slightly, or another valve within the sealed brew circuit. The "problem" you perceived (which I'm not sure is a problem) is subtle in the reasons why it happens and without further information it's difficult to be 100% sure, but I'm 95% sure theres nothing wrong that requires fixing. Rotary pump failure normally manifests quite differently.



El carajillo said:


> I have read in a coupe of articles that rotary pumps are not happy being tank fed due to lack of pressure as they are intended to "push" water rather than pull and push.
> 
> I believe that because of this and the increasing use of them inPro/sumer M/ch they have been improved /modified to overcome this problem.


I think you can not worry about this in the Duetto and the pumps have not been modified in any way. The manufacturers specification for these pumps is a max 6ft draw, so there is no problem having to pull water from a tank.

Please don't be so keen to descale your machines, far better to change the water you use.


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## MrShades (Jul 29, 2009)

Thanks Dave - and rest assured that I certainly Molycote 111 or whatever it's called thoroughly after a descale or chem back flush.

I water back flush very frequently and use Ashbeck water exclusively these days so don't descale very often or overnight!

The original problem hasn't reoccurred and my Duetto is still working flawlessly after 4 years of daily use... albeit with the smaller 0.5mm gicleur now (but the original one still looks perfect after a quick wash and brush up!)


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