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Permalink Reply by Brady on April 8, 2013 at 5:24pm

Hi John.

The Z11 AT is an odd espresso machine. Think of it as a hydraulic lever machine - it uses incoming water pressure to load a spring which then generates the brewing pressure. The shot will experience a pressure ramp up at the beginning of the shot as well as a ramp down at the end. It's a fascinating mechanism and system. That does mean that is wastes quite a bit of water though.

I don't recall exactly how the last one I saw was hooked up, but what you describe sounds right. Check Rancilio's website for installation documentation?

Do not add a pump - it wouldn't work.

Don't backflush with a blind portafilter either - since it's closer to a lever machine in function,there's no 3-way valve or exhaust port.

Hope that helps.

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Permalink Reply by John Bresler on April 8, 2013 at 8:27pm

Thanks for the reply.  This helps alot.  I've looked at rancilio's documentation and it is so vague that even the 20 year espresso machine repair veteran could't figure it out.  He has placed a call to Rancilio which I hope sheds more light on this when he gets his call returned.

I'm only seeing 6 bars of pressure on the machines gauge when I start the shot and there's not much fluctuation on that gauge through the shot.  It doesn't appear to be building pressure.  In Rancilio's documentation of the group head there's no spring, at least not a big spring like you see in lever machines.  It's a piston.  I'm wondering if the pressure is related to water hookup or if I'm just pulling the shot wrong.   

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Permalink Reply by Brady on April 9, 2013 at 3:45am

Hmmm. Will dig that schematic out. Yes, it's a real head scratcher - it was like nothing before and nothing since.

I wouldn't put much faith in the machine gauge. You should check what you're actually seeing at the group. Not sure what you could do to bump the pressure if there was an issue. There are guys at Rancilio tech that are familiar enough with these machines to help you though.

The one I worked on had been lovingly restored for my client by a Cuban guy in Florida. It was gorgeous, and came with about a dozen hang tags to help with installation and maintenance - too bad they were in Spanish. Will post some pics later.

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Permalink Reply by John Bresler on April 10, 2013 at 11:18am

I've been doing more research on this machine to include the Z8 and Z9 AT models.  It seems there's a common theme with taking 2 bars and building 9 bars of pressure from it.  Do you think that maybe I should reduce the input water line pressure to 2 bars? 

I'm still not sure that I have it hooked up correctly.  I did some reading on the La Cimbali M15 TC which has a similar concept with the piston using water to move the piston up and then down.  The Cimbali has two water inlets, one to the boiler and one to the top of the group heads.   This Z11/AT has two water taps, the left one leads to the boiler - but it also leads to the top of the left group.  The other water tap leads to the top of the right group.  Also, if you look at the two groups, they are also connected in line with each other.  I've added a pic so you can see the top of the groups.  You can see the copper pipe coming to each group and breaking off into smaller pipes connecting the two groups on the top side.

Attachments:

• TopofGroups.jpg, 1.3 MB

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Permalink Reply by Brady on April 10, 2013 at 11:29am

Did you measure actual pressure at the group yet?

The inlet ports on each group are connected to each other, as are the outlet ports. Seems logical that whichever one leads to the boiler fill solenoid is the inlet one. I'd bet that there are additional branches on that same line that lead to the heat exchangers.

Reducing line pressure in an attempt to boost pressure at the group sounds counter-intuitive.

John Bresler said:

I've been doing more research on this machine to include the Z8 and Z9 AT models.  It seems there's a common theme with taking 2 bars and building 9 bars of pressure from it.  Do you think that maybe I should reduce the input water line pressure to 2 bars? 

I'm still not sure that I have it hooked up correctly.  I did some reading on the La Cimbali M15 TC which has a similar concept with the piston using water to move the piston up and then down.  The Cimbali has two water inlets, one to the boiler and one to the top of the group heads.   This Z11/AT has two water taps, the left one leads to the boiler - but it also leads to the top of the left group.  The other water tap leads to the top of the right group.  Also, if you look at the two groups, they are also connected in line with each other.  I've added a pic so you can see the top of the groups.  You can see the copper pipe coming to each group and breaking off into smaller pipes connecting the two groups on the top side.

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Permalink Reply by John Bresler on April 10, 2013 at 9:43pm

Well, I'm not putting anything past this machine.  it has some very interesting behaviors.  for example, the left grouphead, if I have nothing in the portafilter, it will fill a 16oz frothing cup with hot water and spill over a bit.  If I have coffee tamped in the portafilter, it will fill two 1.5oz shot glasses with just a bit of excess... not perfect, but not 16oz's.  The right grouphead is very similar accept if nothing is in the portafilter, I get about half of a 16oz frothing cup of hot water, but with the portafilter tamped with coffee, it fills two 1.5oz shot glasses with just a tad over.

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Permalink Reply by John Bresler on April 10, 2013 at 10:01pm

Also, here's some text from a previous discussion in 2011 on an AT machine that makes me think that reducing the bars at input might be necessary.

Reply by Mathew on August 28, 2011 at 6:58pm

pure physics! the surface area of the diaphragm is about 5x the size of the the surface area of the piston and the line pressure is about 5 bars so 5x5=25bars. That's not the precise math because I don't have the parts in front of me to measure the size for sure but there is where the pressure comes from.

Reply by Brady on August 28, 2011 at 7:02pm

So maybe a line pressure reducer is in order? Dropping it to 2 bars ought to do

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