Peppina Marries MiniGaggia - Page 26

[timo888]

The kicker is that you could experiment with both flat and falling profiles.

Now that's making a virtue of necessity. If you don't have temperature stability but temperature creep (up or down as the case may be) let's savor the results?

The central design tenet of the Beast is a flat temperature profile. That's where it all began, way back with Jim Schulman's remarks that the Peppina's design was just too simple to overheat or fluctuate intra-shot.

To suggest a design that radically alters that core tenet of temperature stability is really to suggest a design for a whole nother machine (as we say in Pennsylvania). It's rather like suggesting the addition of a combustion engine and a propellor to a man designing a balloon. "Oh, you mean a Zeppelin?"

Regards
Timo

[hbuchtel]

Timo, explain how this HX design lacks the ability to produce a flat temp profile!

Henry

[timo888]

Henry,

You specified that the water temperature in your boiler is at espresso brewing temp, not superheated. Let's say 202°F.

As you pull the shot, cool water enters the boiler at the same rate hot water in the HX tube is leaving it. Let's say that the extraction happens over a period of 30 seconds. So if ~60ml hot water flows onto the puck, ~60ml cool water flows into the HX tube, that would be a 2.0ml /second flow rate.

I ran another crude test with the Caravel. Brought it to 200°F and then, over a period of 30 seconds, dribbled 60ml of cool tap water into the kettle. Water temperature in the kettle dropped by about 5° with the heating element on. Again, a crude test, and not apples-to-apples, but the best I can do under the circumstances.

The intra-shot temperature fluctuation might be kept minimal with the right combination of factors. With the right tweaks your design could qualify as flat enough.

--a fairly large volume boiler (an open kettle really since it's not under pressure)
--the HX tube is not coiled in such a way that cold water runs adjacent to hot water
--the incoming cool water is not very cold
--the heating element respond quickly to the drop in temperature but doesn't overshoot

The longer the shot (i.e. the more restricted the flow), the more stable the brew temperature would be (at least with respect to this issue of cold-water influx).

Regards
Timo

[hbuchtel]

Henry,

You specified that the water temperature in your boiler is at espresso brewing temp, not superheated. Let's say 202°F.

As you pull the shot, cool water enters the boiler at the same rate hot water in the HX tube is leaving it. Let's say that the extraction happens over a period of 30 seconds. So if ~60ml hot water flows onto the puck, ~60ml cool water flows into the HX tube, that would be a 2.0ml /second flow rate.

I ran another crude test with the Caravel. Brought it to 200°F and then, over a period of 30 seconds, dribbled 60ml of cool tap water into the kettle. Water temperature in the kettle dropped by about 5° with the heating element on. Again, a crude test, and not apples-to-apples, but the best I can do under the circumstances.

The intra-shot temperature fluctuation might be kept minimal with the right combination of factors. With the right tweaks your design could qualify as flat enough.

--a fairly large volume boiler (an open kettle really since it's not under pressure)
--the HX tube is not coiled in such a way that cold water runs adjacent to hot water
--the incoming cool water is not very cold
--the heating element respond quickly to the drop in temperature but doesn't overshoot

The longer the shot (i.e. the more restricted the flow), the more stable the brew temperature would be (at least with respect to this issue of cold-water influx).

Regards
Timo

Ok, good response. I hadn't thought about the incoming water affecting the temp of the water in the boiler (which would have the effect of slightly lowering the temp of the brew water in the forward part of the HX tube.

Experimentation is required, but I think a flat brew water profile (BEFORE THE WATER TOUCHES THE PUCK! that is another story!*) is obtainable.

First, for a flat enough profile: Long flat boiler with a long horizontally articulated (?) HX tube.

Why?

Boiler length: Besides the obvious ergonomic benefits (lower center of gravity), a long (back to front, not side to side) boiler (with the group at the close end) would reduce the transfer of COLD (via the water in the boiler) from the intake water to the portion of water used for brewing.

HX articulation: Keeping the length of the HX line horizontal would prevent pockets of colder and hotter water that would arise with a vertically coiled tube.



By adjusting the dimensions of the boiler and the articulation of the HX tube, these two details would be enough to keep the temp profile flat enough.

Now, a FLAT profile design: Split the boiler in two.

The first boiler would bring up a generous (several shots worth) of water to brew temp. The second would simply maintain that temperature and warm the group.

Remember that a kettle design is not perfect. Fluctuations of temperature within the kettle (heat escaping upwards, proximity to the heating element etc) mean that a "Flat" temperature profile is flat only in name.

* I'm serious about the importance of having the ability to experiment with a falling temperature profile. There is no particular evidence that a flat temp profile produces a better espresso, on the contrary many people (this is second-hand information) think a profile that starts too hot and falls is better. (I will search around for some quotes). Although flat profiles are the fashionable thing around here (perhaps with good reason), if it turns out that falling profiles are better in some way I'd hate to be stuck with a machine that couldn't do that too. (this doesn't reflect very well upon me, but hey . . . )

NOTE: Having a closed kettle rather then an open kettle would be the way to go with this HX design. Reducing (controlling) the amount of heat and water vapour lost could only be a good thing.

Henry

[timo888]

Henry,
The horizontally articulated HX tube and oblong boiler shape seem like good ways to mitigate the effects of the cold-water influx. An additional thing would be to warm the water up before it hits the HX tube, by loosely coiling the copper feed tube from the reservoir around the outside of the dedicated pressurized steam boiler. If the steam boiler is off then you would have a slightly cooler shot.

I have had some very nice shots at 195°F and a drift of a few degrees cooler probably wouldn't hurt as long as the extraction was predominantly in the sweet spot. I mainly try to avoid overheating the shot.

Regards
Timo

P.S. By "closed" boiler I mean "under pressure" rather than "with a lid". It would make sense to put a lid on the HX boiler with a few simple vent holes in it as a failsafe against pressure buildup.

[hbuchtel]

So what do you say, Timo? Peppina marries Achille?

Henry

[timo888]

There's not a single aspect of the existing design, with the possible exception of the drip-tray-grate that could remain as is, if the heat-exchanger kettle were retrofitted onto it, Henry. So why not start a new thread? It would be fun to have two designs going at once. The design you've proposed, with its displaced piston and hydraulic/gravity feed, is much closer to the Conti Comocafe. So why not get that storyline going? Achille and the little Conti And anyway, Peppina is occupied at the moment with MiniGaggia; she is his constant companion and shows no signs of fickleness.

Regards
Timo

[hbuchtel]

There's not a single aspect of the existing design, with the possible exception of the drip-tray-grate that could remain as is, if the heat-exchanger kettle were retrofitted onto it, Henry. So why not start a new thread? It would be fun to have two designs going at once. The design you've proposed, with its displaced piston and hydraulic/gravity feed, is much closer to the Conti Comocafe. So why not get that storyline going? Achille and the little Conti And anyway, Peppina is occupied at the moment with MiniGaggia; she is his constant companion and shows no signs of fickleness.

Regards
Timo

Alrighty, will do.

There are a few elements which would be shared, I imagine, such as the lever assembly allowing for both manual and spring power.

I don't know much about the Comocafe, the one (?) user here hasn't found a PF for his I believe, so I'll keep the Peppina reference if you don't mind!

Henry

[timo888]

Alrighty, will do.

There are a few elements which would be shared, I imagine, such as the lever assembly allowing for both manual and spring power.

I don't know much about the Comocafe, the one (?) user here hasn't found a PF for his I believe, so I'll keep the Peppina reference if you don't mind!

Henry

I don't own a trademark on the Peppina name, Henry. But one could wish you weren't treating her as a broodmare

The Comocafe's design resembles the Peppina's, but in addition to the reversed piston, it has the tubing and one-way valving closer to what your design will require. There is also a degree of visual resemblance between the Comocafe and the Achille, both of which use clear-glass reservoirs on the top of the machine.

The Comocafe is pictured in the Incomplete List of Gravity Levers thread. The machine is described somewhere here on the forum.



The Comocafe's brew water is drawn by gravity and suction down from the kettle through a tube and into the piston chamber. The piston pushes the water up through a tube and then out to the group. A backflow-prevention valve prevents the water from being forced back into the kettle.

Now, if the Comocafe had a cool water reservoir placed behind its kettle, or on the side of the machine opposite the lever for better balance, water could be drawn from the reservoir, through the HX-kettle, and down into the piston chamber.

You might even insert a thermoblock between reservoir and HX kettle to bring the water up to temperature, using the HX-kettle either to raise the water a few more degrees to the desired temperature or to absorb excess heat if the thermoblock had overshot the mark. You might then be able to use the same thermoblock for steam as well, using the HX-kettle to buffer the undershot and overshot temperatures.

Most impressive, like the Centre Pompidou in Paris, the HX's copper coil works would be visible through the glass

Regards
Timo

[hbuchtel]

I don't own a trademark on the Peppina name, Henry. But one could wish you weren't treating her as a broodmare

Very well, out of respect for La Peppina's chastity I will rename it.

I think I found the thread you were talking about- Pump on Conti Comocafe does not work.

Now, if the Comocafe had a cool water reservoir placed behind its kettle, or on the side of the machine opposite the lever for better balance, water could be drawn from the reservoir, through the HX-kettle, and down into the piston chamber.

You might even insert a thermoblock between reservoir and HX kettle to bring the water up to temperature, using the HX-kettle either to raise the water a few more degrees to the desired temperature or to absorb excess heat if the thermoblock had overshot the mark. You might then be able to use the same thermoblock for steam as well, using the HX-kettle to buffer the undershot and overshot temperatures.

Most impressive, like the Centre Pompidou in Paris, the HX's copper coil works would be visible through the glass

Regards
Timo

Git them ideas over to Conti marries Achille!

Henry

[espressme]

Hi Timo,
Now that you've settled the lever head, :?
An idea for the "Beast" group is circulation of water through it but not like the regular HX. It would be similar to the "Achille" in having a pre pull circulate kettle temperature water through and out of the grouphead to make nice nice convection in the kettle and then to fill the piston from the kettle for the shot. One pull two kills! At the exact temperature!
Very simple to accomplish and for the small increase in money a significant advance! :o No electronics here! :!:
And it works spring or direct.8)
:?: Any one else out there? :?:
Best to all
Richard / espressme

Hello Tim,
This thread just came up again, I don't remember seeing it before:
http://www.home-barista.com/lever-espresso-machines/clevis-to-lever-further-explorations-in-espresso-space-t1243.html#top
The first few entries say it all!
Regards
espressme

[timo888]

An idea for the "Beast" group is circulation of water through it but not like the regular HX. It would be similar to the "Achille" in having a pre pull circulate kettle temperature water through and out of the grouphead to make nice nice convection in the kettle and then to fill the piston from the kettle for the shot. One pull two kills! At the exact temperature!

I do see the benefits of various kinds of circulations, Richard, but they apply to designs where you are trying to maintain the ability of the group to sink off excess heat. The Beast will not have that particular issue because its brew water is only a couple of degrees above desired brew temperature as it leaves the unpressurized kettle. Moreover, the Beast doesn't have a massive group that could take such a channel drilled into it; the Beast's group simply holds the PF in place.

Now, the Achille's piston chamber contains cool water, according to the details revealed in the unfolding saga. With its piston upstroke, cool water in a vestibule above the piston flows down through a tube in the piston itself into the now empty piston chamber. Then, with the piston downstroke, that cool water in the chamber is forced into the HX system. The HX system runs through the boiler and back out through the dispersion block to the puck. When cool water is pumped into the HX tube by the piston, hot water already in the HX is pushed out to the puck.

The question on the table is, what is the best way to ensure both inter-shot and intra-shot temperature stability on the Achille? Does it involve a cooling flush? How much? What's the best starting temperature on the extraction? Will a higher starting temperature keep the heating element off for a longer time, preventing temperature overshoot mid-extraction? Does bringing cool water down into the piston chamber and allowing it to linger there for 'n' seconds figure in the equilibrium equation, or are the effects of the cool water on the group's heat-sinking negligible?

Regards
Timo

[espressme]

I do see the benefits of various kinds of circulations, Richard, but they apply to designs where you are trying to maintain the ability of the group to sink off excess heat. The Beast will not have that particular issue because its brew water is only a couple of degrees above desired brew temperature as it leaves the unpressurized kettle. Moreover, the Beast doesn't have a massive group that could take such a channel drilled into it; the Beast's group simply holds the PF in place.

\
Hi Timo,
The thought was to assure the air cooled group would be at the same temp as the liquid in the boiler. Accomplished by a simple (?) hollow "L" channel welded around the group and flushed by the upstroke of the piston drawing water through the channel and expelling it into the kettle, mixing all liquid together - ( and perhaps preventing temperature stratification.)

This happens before the intake fill and down-stroke. ( up-stroke to Peppina fans!) This could be a useful (? no hole in piston !) replacement for the hydraulic lock preventer one way valve in the piston.

The one way valve would then be on an outlet of the channel into the piston cylinder. Then the group channel water would be changed by the first upward movement of the piston.

Complex? maybe! Useful? who knows! Possible? yes.
Regards
richard / espressme

[timo888]

system is acting up -- deleting a duplicate

[timo888]

system acting up--deleting a duplicate

[timo888]

The thought was to assure the air cooled group would be at the same temp as the liquid in the boiler.

The goal is to achieve the design intent through the simplest means possible, using Occam's Razor at every turn
(avoiding multiple entities when one will do). The integral kettle/group achieves this.

The conductive part of the Beast's group is not made of brass but of stainless steel; it consists of the piston cylinder which is situated inside the kettle, where it is bathed in brew water; it extends down and out of the group to become the dispersion screen housing:



That inner cylinder is all one tube.

The bell of the group (not shown) is just a way to lock the portafilter in place, a PF-harness. It has a flange that is bolted to the kettle flange. Sorry if the wire-frame obscures this, but the bottom flange belongs to the PF-harness (not shown) and not to the inner tube.

To prevent too much heat from being conducted to the PF-harness via the flange-to-flange union, there will be an insulating gasket between the two flanges. The thickness of the gasket and its insulating capacity remain to be determined.

Heat will also be conducted down the integrated piston cylinder/dispersion screen tube. But since the piston cylinder is bathed in brew water inside the kettle, I don't think we don't need to worry much about regulating this conduction. It's the heat from the heating element around the outer kettle wall that is the main focus.

Regards
Timo

[espressme]

The thought was to assure the air cooled group would be at the same temp as the liquid in the boiler.

The goal is to achieve the design intent through the simplest means possible, using Occam's Razor at every turn
(avoiding multiple entities when one will do).

He was a sharpy NO?

Heat will also be conducted down the integrated piston cylinder/dispersion screen tube. But since the piston cylinder is bathed in brew water inside the kettle, I don't think we don't need to worry much about regulating this conduction. It's the heat from the heating element around the outer kettle wall that is the main focus.
Regards
Timo

So, you have decided upon a band heater?
Best regards
Richard

[timo888]

Band heater makes most sense given the design, I think. Keeps the inside of the kettle clear of stuff and easy to clean. No need to drill holes in the kettle for the element. Easier to install and replace. No need for a custom design. Bands come ready for a PID upgrade.

Regards
Timo