Pros and cons - Hx vs Dipper - Page 3

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Tio Tom
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#21: Post by Tio Tom »

[quote="Satchmo780"]I may be missing something, or having difficulty with terminology, but if the brew water is directly from the boiler using a thermosyphon to heat the group, wouldn't this be a dipper with a thermosyphon?

Thanks for your comment. The heat exchangers do not perform the function of an 'exchanger.' Since they are being fed with hot boiler water that surrounds them in the boiler, there is no heat 'exchange' to take place. Their first function is to heat the brew heads by means of thermosyphon. So in that 'sense' the use of the term 'exchanger' is confusing. Maybe there is a better term. There is no 'dipper' since the water for brewing is drawn from the attached 'exchanger' which is their second function in the machine.

I am getting close to hooking the machine up on my bench and see what happens. I am still a little 'shaky' on how to wire but once I get over that hurdle I can see what happens. Thanks again.

Satchmo780
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#22: Post by Satchmo780 »

So it's a dipper with a thermosyphon.
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baldheadracing
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#23: Post by baldheadracing »

I'd call it a hot-fed HX. The feed is at boiler pressure instead of line pressure, and the feed is at the top (hot) of the HX instead of the bottom (cold).

The heat exchanger is still a heat exchanger - the water entering the HX at the bottom is colder than the water leaving the HX at the top. Heat is still being exchanged.

The water leaving the top of the HX mixes with water from the boiler to feed the hot side of the thermosyphon (going to the group). There is no dipper tube directly and exclusively connecting the water sitting in the boiler to the output of the group.

One way to think about it is to first consider the thermosyphon circuit in isolation. Water being added does not change the direction of the thermosyphon flow - to keep the flow going when water is removed (extraction), one has to feed in cold water at the bottom, or hot water at the top.
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Satchmo780
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#24: Post by Satchmo780 »

baldheadracing wrote: There is no dipper tube directly and exclusively connecting the water sitting in the boiler to the output of the group.
Ah -- this is where I was getting hung up, as I thought that the tubes going to the group were exclusively coming from the boiler.

It really is quite drastically different from a traditional HX where the the brew water doesn't mingle with the boiler water.
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homeburrero
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#25: Post by homeburrero »

I think in the context of this thread, titled HX vs Dipper, you would put any machine that pulls brewing water from the steam boiler a dipper, irrespective of whether it has an HX-like chamber that supports a thermosyphon loop. The maintenance issue associated with mineral concentration in the steam boilers would be the same for all 'dippers' defined this way. (I.e., a 'dipper' would not experience the steam boiler concentration issue that an 'HX' might have.) There have been a few terminology confusion discussions about this in the past. Here's just one: Stalling Thermosyphon

So you can have 'dippers' that have thermosyphons, like the Faema Lambro, and you can also have true HX machines that don't have thermosyphons, like the VA Athena.
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austted
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#26: Post by austted »

I have found this to be a very informative thread especially the discussion about Tio's Palanca.

I consider the Hx / Ts arrangement should give heat stability to a lever group because the thermosyphon (Ts) effect allows more rapid hot water flow from the heat source (eg boiler) to the cooling lever group.

I noted that Curtis (pizzaman383) wrote "This design looks similar to the original londinium design"



I found this schematic in a review of the Londinium I in kaffeewiki - https://www.kaffeewiki.de/wiki/Londinium_I
I suspect it was drawn by Reiss Gunson but cannot confirm that. I found it useful in that it explains the TS link between the lever group and the boiler.

What I do not fully understand is how changing the inlet water pressure via the pump, or a mains water regulator in the case of a plumbed in unit, affects pre infusion (PI) pressure in a lever machine. Londinium users are advised to use a higher inlet pressure ( say 3.5 bar to give an example) for a light roast but reduce it for a dark roast.

I have not been able to work out how changing the inlet pressure can change the PI pressure senses when you pull the lever down. I looks to me the group is open to the boiler (steam) pressure (typically around 1 bar) when the lever is pulled down.

Can anyone explain this?

btw I have got into lever espresso after acquiring a 2 group Royal Vallelunga Leva machine Royal Vallelunga Leva

Regards
Ted

Marmot
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#27: Post by Marmot »

Hi Ted

Do you mean the PI pressure in an HX layout?
There you have a direct connection between the water mains and the portafilter once you pull down the lever. You have some steam pressure inside the HX but when connected to the water mains you also have the pressure from the water line which is usually more and pushing from behind. So a change in inlet pressure will affect preinfusion. The pressure inside the service boiler has no effect on preinfusion in an HX machine since it usually is not connected to the HX. I don't know the Londinium design though.
On a dipper machine it is like you assumed that only boiler pressure affects preinfusion and is also necessary to get water from the boiler to the group.
I have a Strega which has an HX layout. I have the version with reservoir and vibration pump. When I pull down the lever the pump gets activated and pushes the water through the HX tube as it would happen when directly connected to the water line. The pump would run up to its maximum pressure or until the overpessure valve opens but I release the lever (and therefore the microswitch for the pump) at my desired PI pressure.
Cheers,
Marco

austted
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#28: Post by austted »

Marco
Thanks for the reply.
Yes I do mean PI pressure in an HX layout and in my case, direct from the water mains via filter and a pressure regulator (currently set at 3.5 bar),

You say "There you have a direct connection between the water mains and the portafilter once you pull down the lever. You have some steam pressure inside the HX but when connected to the water mains you also have the pressure from the water line which is usually more and pushing from behind. So a change in inlet pressure will affect preinfusion. The pressure inside the service boiler has no effect on preinfusion in an HX machine since it usually is not connected to the HX. I don't know the Londinium design though."

My confusion arises from the fact that I understand the Hx circuit is in contact with both the boiler water and the portafilter once you pull down the lever. That Londinium schematic I posted above certainly suggests it



This picture of the inside of a Faema Lambro boiler taken from one of IamOiman's restoration projects also shows that the Hx tube that transects the boiler provides a path between the steam pressurized boiler water and the water in the HX that accesses the lever group via the hole in the side of the tube.

The other thing I noticed is that I cannot see a separate cold water pipe from the mains inlet entering the Hx circuit of any of the Hx lever machines that I have checked pics of and that includes the Londinium Compressa ( a plumbed in model) or my Royal Vallelunga Leva which is marketed as a Hx unit. My machine's dual pressure gauge clearly reads 3.5 bar (on the inlet manifold near the non-return valve) and 1 bar (inside the top of the boiler). The same applies to Tio's Palanca which according to the schematic has HX tubes that on the outside appear much like that on the Lambro.

Does your Strega have a separate cold water line from the pump to the Hx circuit?

Regards
Ted

austted
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#29: Post by austted »

I just realized homeburrero described the Faema Lambro as a 'dipper' that has a thermosyphon in this thread
and that the Victoria Arduino Athena Leva is a true Hx that does not have a thermosyphon.

baldheadracing posted the schematic here Lever groups and their compatibility - Conti vs Victoria Arduino Athena . This one clearly has a cold water feed to the Hx but is not a thermosyphon.

Marmot
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#30: Post by Marmot »

I think machines like the Lambro are called open HX machines.
Your Vallelungo Leva seems to have more or less the same design. I checked the Londinium L1 and it seems also to use this kind of layout.
I don't know the actual design of the boiler from the L1 but in a forum they mentioned that preinfusion pressure is never higher than boiler pressure as is the case with a dipper. The pressure on the inlet line does not really matter. It only influences at what rate the boiler is being filled up.
The Athena Leva is also interesting. I wonder how this design without thermosiphon affects recovery time of the group. I guess it is a good design for commercial use if it takes a long time to heat up but you are able to do a lot of shots in succession.