Positive pressure, PID Pavoni: world domination begins

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matadero210
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Joined: Mar 08, 2007, 4:19 pm

Postby matadero210 » Apr 08, 2007, 6:41 pm

All,

I'd like to share my first Pavoni mod. I started with a pre-M europiccola and drilled the heater/base to include ports for TC and water inlet (1/8" npt). The whole is mounted on an oak base with PID controller, power switch, and steam override switch.

Image

From the back you can see the stainless flex tube that connects to my kitchen faucet.

Image

I'm just learning about how this works, but the first shots were very nice. The water supply is regulated to 20psi, so I can leave the water connected and pull shot after shot. It takes <1min to stabilize temp after each shot (and the cold water admission). 20psi is on the edge of too rough for pre-infusion, so I can also close the water inlet valve and do a more gentle pre-infusion (I monitor this with a bottomless PF). The TC is t-type (mcmaster.com) and the PID (which comes with internal 10A relay) is from auberins.com. More details to follow (once I stop shaking from caffeinosis) after I master use of the machine.

share and enjoy,
raj

PaulTheRoaster
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Joined: Nov 20, 2005, 10:38 pm

Postby PaulTheRoaster » Apr 08, 2007, 7:12 pm

Awesome. Did you come up with some kind of expansion valve for when the cold water comes up to boiler temp? Wouldn't want the thing to explode.

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matadero210
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Postby matadero210 » Apr 08, 2007, 7:29 pm

Yup,

I also relieve excess pressure while flushing/heating the head.

Image

I use a commercial anti-hammer assy first, but a simple expansion tank seemed better.

r

Javier
Posts: 355
Joined: Mar 13, 2006, 12:24 pm

Postby Javier » Apr 08, 2007, 11:41 pm

Raj,

Oh man, that is impressive. Very ingenious.

The water supply is regulated to 20psi, so I can leave the water connected and pull shot after shot. It takes <1min to stabilize temp after each shot (and the cold water admission). 20psi is on the edge of too rough for pre-infusion, so I can also close the water inlet valve and do a more gentle pre-infusion (I monitor this with a bottomless PF).


Before actually pulling the shot, do you get resistance at the lever from the uppermost position (i.e., right after pre-infusion)?

Javier

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matadero210
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Postby matadero210 » Apr 09, 2007, 12:19 am

Javier,

There are two ways of dealing with pre-infusion. The problem arises because Pavoni's are not really air-tight--only partially so. They leak slightly. One method is to open the inlet valve and jiggle the lever until the downward pressure feels right and then close the inlet valve. After 10-20 seconds the temperature stabilizes and I can pull the shot--it takes about 5# of upward force to raise the lever.

The second method is to leave the inlet valve open for the entire time. In this case it takes about 15# to raise the lever and the pre-infusion is a bit fast (about 5 seconds to visible liquid on the bottom of the basket).

Both of these methods work fine with a warm machine. Coming from cold, the second method has too much false pressure, which I relieve with a warming blank shot.

After the pre-infusion, I feel some pressure at the top of the stroke. I think your question is getting at the issue of whether the cylinder is full of water or water+air. I haven't worked this out, but with the higher pre-infusion pressure (second method) it seems that I get almost all water. I don't really understand how the Pavoni can take advantage of a 45ml stroke--I tend to get ~35ml at best for a single pull. I'm looking at ways of changing the pre-infusion to start earlier (before the lever is fully raised), but I'm not sure if I'll be able to incorporate that mod.

raj

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espressme
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Joined: May 31, 2006, 10:47 pm

Postby espressme » Apr 09, 2007, 4:38 am

Hello Raj,
Now you've done it! :lol: That is something I've wanted to do to mine in the course of a rework.
How do you prevent the boiler from overflowing when the boiler is cold and the water is on. Or, in other words, how do you monitor the water level? Do you fill to a point on the sight glass, or does the 20PSI balance the steam pressure and the whole thing becomes moot?
Again WOW!
sincerely
richard / espressme
richard penney LMWDP #090,

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timo888
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Joined: Feb 28, 2006, 4:23 pm

Postby timo888 » Apr 09, 2007, 9:07 am

Do I understand correctly that, for brewing, you temporarily "convert" the machine into an open unpressurized kettle (albeit with a boiler cap) by keeping the boiler temperature below boiling? Afterwards you can reset the PID so that the temperature will rise to above boiling and the machine can be used to produce steam?

I realize you might not have measured these things yet, but questions about brew temperature spring to mind.

If the temperature of the water inside the boiler is ~198°F, what is the temperature of the water hitting the puck? How much heat does the group sink away? With the Peppina's relatively lightweight group, as a point of reference, there is a drop of only a couple of degrees between kettle water temperature and brew temperature. But with the heavy brass group of the Pavoni, which is designed to handle 212°F water and bring it down into brewing range, one would expect a drop of more than a couple of degrees.

You mention above that it takes 1 minute to stabilize after a shot. After an influx of ~50ml of cold mains water, how many degrees does the water temperature in the boiler drop? When pulling multiple shots, is there an upward brew-temperature creep? With shots at 2-minute intervals, say, does the group sink away less and less heat with each shot, so that at some point, the boiler temperature and the brew temperature are quite close to one another, only a couple of degrees apart? Or does the group also recover in 1 minute?

Regards
Timo

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matadero210
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Postby matadero210 » Apr 09, 2007, 11:32 am

All,

Thanks for all the great questions. I'll do my best, but there is still a bunch of metrology to do (I love that word). For those who care, a peek up her skirt (or his kilt):

Image

NB: I had the two-element brass heater. I drilled out and removed the 200W heater and removed the heat shield. This improved circulation around the element (if that helps I have no idea why). The 200W heater was in the way of my TC, a 1/16" x 8" stainless grounded probe.

Operation goes like:

1. turn on gate valve to water. This lets cold water into the 20psi regulator (fixed, but I've got a better one on order).
2. power up the pid/heater and let heat.
3. because I live in fear of electrocuting myself, place measuring cup to catch group+opv drips.
4. at 50C, wiggle lever to check boiler pressure. if too high, close inlet water and drain by raising lever.
5. at temperature (95c at present), open inlet valve (bringing boiler to 20psi), and let 100ml run through head to pre-heat.
6. wait 1 minute (boiler may cool with inlet water, but comes back). pull shot.

5. (alternate) at temperature, open and close inlet valve, and let enough water run through the heat to pre-heat without exhausing the boiler pressure. keep inlet closed and use reduced pressure for shot.

I haven't been able to measure the puck temp, but taste is great and consistent. water in the measuring cup is 180f. I had plans to insulate the head, but I don't want to uglify too much. Maybe a wooden box around the head followed by spray-in foam. That would eliminate the heat-sink capability of the head. I also have a heater band that I might use on the head, but I think I'll wait. Pre-heating the head with a blank shot is sooo easy when plumbed-in.

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matadero210
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Postby matadero210 » Apr 09, 2007, 11:33 am

Timo,

yes, right now I set the pid to 105c for steam. there are two switches on the panel, but not yet connected. One for pid power, and the other for pid override. That will be the steam switch.

Regarding the temperature drop. With the basic procedure, it varies, because the pressure regulator is a bit sticky. Sometimes a shot results in almost no inlet water, but with full inlet about 9C drop which takes ~30sec to recover (the pid is pretty good once auto-tuned). In the alternate procedure (with no inlet during the shot), the 9c happens when I toggle the inlet. In 4 tries the variation was 8-10c.

As for your last question, my reasoning is that if I always flush with 95C water 1 minute before the shot, I'll always have the same group head thermal loss (whatever it might be). unless I rig up something better for measuring puck temp, I'm not sure how to test this. The copious flushing may not really fully pre-heat the head, but it seems to come close.

Measuring in the cup at 1 minute intervals, drawing 50-75ml from the shower screen to cup, with boiler set to 95C:
183, 187, 187, 186, 188F.

I think most of that variation was in the volume drawn (since its pre-infusion water, not real shots), and pre-infusion water is less affected by head temp that real shot water. I'll try to repeat the experiment with real shots shortly.

r

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TUS172
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Postby TUS172 » Apr 09, 2007, 5:26 pm

So you allow water into the unit and then turn the water off to operate the unit and then between shots allow more water into the system? Otherwise you would be over pressured during operation and forcing water out the OPV ...Right or Wrong?
Bob C.
(No longer a lever purist!)
LMWDP #012