Hello everyone,

 

So I came across a Rancilio AT at the roaster I do service work for and I decided to play with it some and restore it having heard good things about the espresso quality.  I also happen to have an arsenal of old parts from a tech we bought out when he retired.

 

anyways I got the groups rebuilt and everything works just fine but I was wondering what some of you think about these machines, I know they waist A LOT of water, (about a quart per shot go's down the drain) but I also noticed the pressure for the group is really high, when I put my pressure gauge on the group it burried the needle! That's over 20 bars! don't worry I put a valve on the bottom of the pressure gauge to be able to relieve the pressure. I did the same thing on a Rancilio Lever and it capped out at 12 bars. The biggest problem I am having with the AT is there is so much pressure at the group it's leaking around the portafilter and I put brand new gaskets on it with no luck. 

 

So what are your thoughts and tips on this machine, is there a way to fine tune it? I realize I'm kinda at a loss and have no idea where to go from here.

 

Thanks Mat

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Can you share pictures? Never seen one before, and have no idea what is going on there. Almost looks like an automatic lever machine? Probably won't be able to help out at all, but I'd love to see what's going on.

Here's some pictures and the exploded parts diagram,

 

Brady you are right it's just like the lever machine with the same piston but instead of a lever and spring you have this crazy hydraulic chamber with a diaphragm.  So when you lock the lever to the left water is routed to the bottom of the chamber pushing the diaphragm up which pulls the piston up. Then you release the lever and water is rerouted to the top of the chamber pushing the diaphragm and piston down and expelling the water in the bottom of the hydraulic chamber down the drain.  Dose that make sense?  I just haven't figured out yet how to control the water pressure forcing the piston down because right now it's climbing over 20barrs! yikes!!! 

 

I'll keep playing and let you know what I find.

 

Wow... that thing is kinda cool. I don't see anything on the schematic, but is there perhaps a jet missing somewhere, or maybe a bypass that isn't working properly?

 

When you talk about water going down the drain... is it coming out of the expansion valve (if there even is one) or is it lost as part of the process?

 

Mike Sabol, have you run across one of these?

 

I know its an older model, but have you tried calling the guys at the Rancilio tech support desk? Sometimes those guys are really into the weird older stuff and may be able to shed some light on the situation.

 

Good luck and keep us posted!

the water going down the drain is the water in the upper chamber that moves the diaphragm up and down you are dumping 30oz for every shot of espresso you pull.  that's a 1:15 ratio vs some RO water systems that are about 1:3 for waste water! Not very green at all.  especially when your dumping filtered water!

I would not reccomend a machine like this for any cafe but it is fun to geek out on!

 

That is a really cool machine.  I've never seen one before.

 

20bar is a lot of pressure.  How is it generated?  I know you said that the water is routed to different chambers, the upper and lower, but it looks like the valves on top of the group can only route water into and out of the upper chamber.  If water is bled out of the upper, and this is a closed system, then the piston would be drawn up via vacuum. When you have the amount of water you want in the lower chamber then you'd reverse the lever, routing water back into the upper chamber.  The problem is that the pressure to drive the piston down needs to come from somewhere.  In a lever machine it is a compressed spring.  In a semi-auto it is the electric pump.  Something needs to be generating the pressure, or vacuum, used to move the water to and from the upper chamber.  The steam in the boiler would not produce those kind of numbers.  The only thing available on a machine without an electric pump would be the pressure generated by the heating of water in a closed tank.  That will generate lots of pressure but very little volume.  The pressure is almost instantly relived when just a few drops of water are removed from the tank.  Not enough to create pressure for the time it takes to pull a shot.  So what, then, is creating that pressure.

 

Typical lever machines have a pressure reduction valve installed before the inlet to the machine.  Perhaps you need something like that to control the incoming line pressure.

 

Where does the water come from for the upper chamber?  Line?  Steam tank?  Independent tank?  Heat exchanger?

 

Can you post some pics of the rest of the insides?  What does that black lever to the left of the portafilter do?  Release water to the drain when the shot is done but there is still pressure behind the piston?

I read somewhere it uses some type of hydraulic system for the shot instead of a lever or pump, weird! Definitely don't know a thing about that machine.

Hey, here's the full machine schematic from the Rancilio website.

great questions Mike,

It's hard to see in the schematic but there are two small veins on the sides of the hydraulic chamber that route water to the bottom.  So water comes in from the water supply and is split, one to the steam tank and the other to the hydraulic chamber.  (The water for the coffee chamber I think is filled with water from the steam tank like other Rancilio lever machines.) The left valve on the top of the hydraulic chamber is the inlet for top and bottom and the right is the outlet.  So slide the top lever to the left which opens the left valve to fill the bottom chamber and opens the right valve to drain the top chamber. Then you twist the bottom lever which releases the lever and reverses both valves so water is now being pushed into the top of the chamber via the left inlet valve and out of the bottom via the right outlet valve. 

 

there is a tube coming off the bottom of the group that I haven't explored yet and I have a hunch that has something to do with the pressure control system,  I'll let ya all know what I find when I have time to play with it some more.

 

Alright, that makes sense.  But what is generating the pressure?  If the water that fills the hydraulic chamber is from the water inlet then that sounds like it is cold water with only line pressure to work with.  Again, not enough to generate 20 bar.

Mathew said:

great questions Mike,

It's hard to see in the schematic but there are two small veins on the sides of the hydraulic chamber that route water to the bottom.  So water comes in from the water supply and is split, one to the steam tank and the other to the hydraulic chamber.  (The water for the coffee chamber I think is filled with water from the steam tank like other Rancilio lever machines.) The left valve on the top of the hydraulic chamber is the inlet for top and bottom and the right is the outlet.  So slide the top lever to the left which opens the left valve to fill the bottom chamber and opens the right valve to drain the top chamber. Then you twist the bottom lever which releases the lever and reverses both valves so water is now being pushed into the top of the chamber via the left inlet valve and out of the bottom via the right outlet valve. 

 

there is a tube coming off the bottom of the group that I haven't explored yet and I have a hunch that has something to do with the pressure control system,  I'll let ya all know what I find when I have time to play with it some more.

 

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. 

 

So maybe a line pressure reducer is in order? Dropping it to 2 bars ought to do...
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.
Matthew, I think you are spot on.  Perhaps I missed what your line pressure is, but take a measure, then reduce accordingly.

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