La Cimbali M32 Bistro problem .. driving me crazy!!

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Coffeefix

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Dec 17, 2014
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I think you could be wasting your time by replacing the group valve/pump.
Are you getting 9bar of pressure at the group? An easy check for your technician who would do this with a filter holder and attached gauge (gauges on machines are often unreliable).
It is possible that lime scale from the internal thermal reserve (water comes from this, not the main boiler) or old coffee keeps jamming the valve - did your technician find any debris in the old valves? Are you back-flushing daily?
Espresso machines of this type make coffee by forcing hot (main boiler too hot for this) water through the coffee at (hopefully) around 9bar. During this process, the pump forces cold water into the machine that displaces the hot through the coffee at 9bar.
This cold water at 9bar then gets heated and the effect is that the pressure then rises in the group/thermal reserve system.
An expansion valve opens, generally set at 12bar, to relieve the pressure - usually a pipe can be seen dripping into the waste under the cup tray when this occurs.
If this expansion valve is stuck or set-up incorrectly the pressure increases too much, often causing the group valve to drip...
 

dchristi

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Jul 16, 2014
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Answers to some of your questions

One more thought... Does your bistro have a brass rotary pump or a vibration pump? Some older Bistros had those I think?

There is not a technician for 500 + miles. However, I was a electronic tech for many years and feel comfortable tearing things apart and putting them back together. Quick summary of this unit- I bought the unit from a Tea/Coffee House in my town. They used it heavily for 5 to 6 years. Not sure if they bought it new or used? So it makes espresso shots, but not correctly. What I mean by that is that it does not produce any creama in the shot. It is just dark coffee. That led me to believe that it was not getting the proper pressure. So, I first thought it might have to do with scale build-up inside the machine. I took it apart and soaked all of the lines in a vinegar solution. All tubes cleaned up nice. I put it back together and put all new screen filters inside where the old ones were. It worked fine after reassembling- but no pressure change. I did some looking around online and found that my pressure should be around 9 bars. It normally sits at 4 bars through the whole process of making a shot. I replaced a kinked hose that went from the pump to a large valve on the left side of machine- no change. I replaced the 5 uf capacitor and it helped the pressure some. Now it sits between 5 and 6 bars. I have tried to make the pressure adjustments with no real change in the gauge. The adjustment was right off the pump with set screw. The pieces in the area were stuck. So I soaked them and was hoping for it to work better, but it did not. I purchased the valve unit that the pressure gauge sits off of. It was used, so I cleaned it well and replaced. No change. My wife wants me to get rid of it now. I found out today that a new pump only runs $300. The thing is we do not use the machine very often. We own a frozen yogurt store and I original bought it to make espresso shots to put in our Ice Blend Coffees/Smoothies. The techs tell me that this machine works better being used heavily rather than a few times a day. So, I might be better off with a different type of unit.

I have had to take the group unit out of the machine to replace screws that fell off the bar that kicks the used shot into container. So I'm not afraid to take it apart. I also had to replace the water level sensor in the boiler and the high pressure sensor board. I set it off when I was tapping on the pump and boiler trying to release any sentiment in the unit.
I do back flush everyday and have a high end water filter on the unit. The parts guy told me today that it is a brass rotary pump. And on many occasions after making a espresso shot, there is water in the cup tray.

Where is the internal thermal reserve? Can I purchase a filter holder and attached gauge?
 

Coffeefix

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Hi, the thermal reserve is behind the group and provides water at a lower temperature than would come from the main boiler - "coffee boiled = coffee spoiled". The group is bolted to the boiler with M6 studs/spring washers/nuts around the rear flange. A few more cross head screws at the front for support. The front facia and frame (this holds the steam and water valves) will need to be removed. The water supply pipe needs to be split where the jet/filter are held below the group behind the stainless panel. A bit of a wiggle and a lift should pop the group off the boiler - it gets stuck by the seals over time. The group usually pulls away from the boiler with the thermal reserve attached to the back. A slight tap with a rubber mallet is all that is needed to split group and thermal reserve if you can't seperate them by hand - be careful when tapping the thermal reserve as it is a relatively soft copper spinning that easily distorts.
Workings: when making espresso, cold water is pumped up the supply pipe to the group passing through the jet/filter (both need to be clear), the water then passes through pipes around the group and the three way valve (designs have changed over time) the into the group at the top (17mm brass nut) and down though a PTFE pipe to the end of the thermal reserve (flow could be the other way around - can't remember!) This then displaces hot water through the coffee. There is an expansion valve on the system that allows for the expansion of the cold water which when pumped in at 9 bar of course expands with the heat.
The pressure (hopefully 9 bar if set correctly) is dependent on the following:
1. The pump works? Squeaking noises as it starts/stops give a clue to wear or not turning - there's a clue at the back of the motor where you can see the motor shaft turning or not... Next, separate the pump from the motor - you should be able to turn the shaft on the back with your fingers easily.
2. Pump pressure - pressure is regulated by the screw or nut (secured by a locknut on some) on the side of the pump. This adjuster alters the amount of water that is able to bypass the pump and alters pressure - notorious for sticking.
3. The expansion valve is set up ok? After making coffee or on initial heat up, the expansion valve is expected to drip a little into the waste trap as the water expands. If the plastic? pipe from this valve continually drips or runs water the pressure in the group cannot build up especially if it is running when attempting to make coffee.
4. Other than pressure, the water flow through the group also needs to be clear - ignoring pressure, do you get decent water output from the group shower plate?
The water in the cup tray after making a shot of espresso is normal. Obviously, the group should be holding 9bar as it makes coffee - when the operation ends the unwanted pressure is released by the 3-way valve into the tray. It does this for a couple of reasons - so that the coffee stops running at the correct time and so that you don't get covered in coffee when removing the filter holder that would otherwise still be holding some pressure.
This is also why you need to back-flush at close of day. The exhausted pressure carries bits of coffee (gradually blocks valve) and coffee oils (these stick to the inside of the group and go stale). The back flushing creates more pressure than normal and the detergent combines to flush out this waste to keep the group fresh. Plenty of flushing after the detergent please!
Italian gauges are often not too accurate so most engineers use a filter holder with a gauge attached to double check.
Good luck!

http://caffetech.com/grouphead-pressure-gauge-various-manufacturers.html
 
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Hampden

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Jan 7, 2015
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Thank you all for this thread. I bought a Cimbali M2 2 weeks ago and have learned a lot from your discussion. There is not a lot of product literature available so your problems and solutions are really helpful.

One point i didn't understand, how do you measure pressure on an m2?

The boiler pressure is visible on the display, but i can't see any indicator of the pump pressure. Do i need to get a separate gauge for this purpose?

BTW: my machine didn't make crema until i opened the top and move the levers that set the grind fineness. By moving the levers i mean unscrewing them from the grinder, tightening the grinder, and reattaching the levers so the control tab week still poke out of the top when the cover is on. First i turned it too far and no coffee came out. Reading 7 on the grinder number scale when viewed from the left of the machine. I backed this off to 9 and now the crema looks good. There would have been no way to get the grind fine enough using only the controls that stick out from the top of the machine. Once you get the grind in the right neighborhood, the external controls will let you find tune the grind.
 
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Coffeefix

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Hi Hampden,
I'd like to help but bean2cup machines... Well, let's just say they aren't my favourite things!
Having said that, the principle is pretty much the same. I used to work with Cimbali machines and a few M52 B2C machines too. I'm pretty sure they had a water pressure gauge inside the machine that was visible when a panel or something is removed? - Try behind the dregs drawer or cup tray. Could be the same with the M2? - worth a look. You certainly need to set the pressure somehow. If there is no gauge to be seen, look for the water pump outlet, there should be a connector somewhere nearby where a simple pressure gauge could be connected.
You sound as if you have done ok with the grinder, many grinders have the amount of adjustment available restricted in some way to prevent staff with little knowledge playing and getting the grind too fine for instance (this can clog up a grinder). In this case there is nearly always a way around this because when the grinder blades are replaced this restriction will need to be altered to enable the new blades to grind within tolerance.
Try:
www.sreweb.com/lockbox/manuals/lacimbali.pdf
 
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CCafe

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Aug 11, 2004
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The M2 pressure gauge can be found on the left hand side of the machine behind the lid (display and buttons) you'll have to open it and look downwards a bit. There is a panel beside the spout that can be removed by loosening the 2 bolts and then just pull the panel out. Newer machines the gauge is tilted up so it can be seen just by opening the lid. Older machines pulling the panel out is the better of the two ideas.
 
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CCafe

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Aug 11, 2004
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Des Moines, Iowa
Before we go any further.

1. This thread has been hijacked and was originally about a M32. Its now been taken over and its about a Cimbali M2.
2. Coffeefix the discussion is about a Super Auto and not a traditional machine. Your trying to trouble shoot a traditional while dchristi is talking about a super auto.
3. The thread has now been hijacked again. I would suggest that both dchristi and Hampden start a new topic requesting help with their M2 issues.

Hampden I've already stated where to find your pressure gauge for adjustment.

dchristi there is one other route before replacing your pump you need to check out. Behind the same panel I told Hampden about you'll find the water manifold with flowmeter and expansion valve. The expansion valve is part of the manifold. You'll see a large flat head screw in the front for adjusting the expansion valve's release rate for over pressure. Underneath the valve you'll see a semi clear tube that is connected to the dump system underneath the brew valve behind the group.

Pull the hose off the dump assembly and see if you can get it outside the machine. Now make a shot. There should be no water escaping during the brew cycle. That line should be dry. If that line is running a constant stream of water or several drips of water then you need to reset the expansion valve. If you have water coming out you'll need to loosen the set screw its a small hex screw on the side roughly 1.5mm. Turn the flat screw clockwise until the water stops. At this point check your pressure on the gauge while making another shot. If it shoots up to 9 or higher you found the problem to your pump pressure issues. There is more to do but troubleshoot up to this point then we'll go the rest of the way if needed.

I've replaced probably 100 M2 pumps since the M2 was released back in 2003. They don't last forever and if you already cleaned the adjustment screw like I said and it still won't make pressure and your expansion valve is working properly then the blame is most likely the pump.


Would one of the mods please lock this thread after this last comment. Thanks CC
 
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