How do thermosyphon lever machines work?

#1: Post by **nirdvorai** » October 15th, 2020, 8:17 am

I'm trying to understand how the family of thermosyphon lever machines works. I know how HX machine work, but when I looked inside the boiler of my Ater Family (same as Bezzera Family and Sama Club) I can only see 2 tubes that goes to and from the group head and end up in the same level inside the boiler. I was under the impression that one of the pipe will be shorter.
And it lead me to more questions:

1.What happen when you push the lever down? what is the path that the water travels from the boiler to inside the group head?

2.while a thermosyphon lever machine is cold and you push the lever and realise- will water flush through the group? or one can only flush when the boiler is up to pressure?

#2: Post by **Bluecold** » October 15th, 2020, 8:35 am

Keep in mind this is about open-thermosyphon levers such as Faema Zodiac-grouped machines, londinium L1, and a host of others, but not machines with a thermosyphon-hx combination, such as the LR.

The thermosyphon flows due to the temperature difference between the group and the boiler. Cold water is denser, and this is what drives the thermosyphon.

When the boiler is up to pressure, water comes out if you pull down the lever. Water comes through both thermosyphon pipes.

#3: Post by **Jake_G** » October 15th, 2020, 8:41 am

nirdvorai wrote:1.What happen when you push the lever down? what is the path that the water travels from the boiler to inside the group head?

When the boiler is under pressure, water will flow through both pipes, under boiler pressure, into the group. An open thermosyphon effectively works like a dipper when the lever is pulled down. Since both TS tubes are submerged, both tubes will draw water.

nirdvorai wrote:2.while a thermosyphon lever machine is cold and you push the lever and realise- will water flush through the group? or one can only flush when the boiler is up to pressure?

No. Since there is no direct path between the top of the piston and the boiler, lever pumps do nothing other than expose the holes in the cylinder. When there is no boiler pressure, there is no motive force to move the water from the bottom of the boiler, up the TS pipes and into the group. There may be a small amount of water that is held in the group that dribbles out, but I would not expect pumps of the lever to do any flushing unless there is pressure in the boiler.

Open HX designs like this are a bit "ambiguous" as to which pipe is hot and which is cool. Once a temperature gradient is established in the group (generally with a flush of water - see below), the convection currents will keep the flow going in whichever direction. When you pull a shot , the group dynamics change and both thermosyphon pipes flow from the boiler to the group. When the system stabilizes, the TS loop can change direction with no ill effect. Sometimes, the loop can stall, which leads to a cold group. The general preventive strategy to avoid this is to do a brief screen-clearing flush after pulling a shot. This tends to jump-start the thermosyphon loop and keep the group idling at the proper temperature.

Cheers!

- Jake

October 15th, 2020, 9:01 am

Thanks Roeland and Jack.
I think i'm starting to understand this. I understand what happen when the boiler is up to pressure and you pull the lever. What I'm missing is what happen while the boiler is up to pressure and the machine is idle. Is there a cycle of hot water coming from the boiler, running to the group and goes back to the boiler colder? and if yes- we don't know from which pipe the cold or hot water running? because it's "open HX"

The attach draw is from and old post, here on HB, on Londinium 1-P by erics.
Can I assume that the Ater Family water flow to the group is the same?

#5: Post by **Jake_G** » October 15th, 2020, 9:57 am

nirdvorai wrote:Is there a cycle of hot water coming from the boiler, running to the group and goes back to the boiler colder? and if yes- we don't know from which pipe the cold or hot water running? because it's "open HX"

That's right.

In general, the "preferred" direction of flow would be into the top fitting of the group and out the bottom. This is because of the density difference between hot and cold water, as Roeland states. However, since the boiler ends of the pipes are at the same level, they both have equal opportunity to feed the group hot water, so it is a known phenomenon that sometimes these loops run backwards and feed from the bottom up. It all depends on which portion of the group is cooler after you pull a shot. The water in the cooler side will "fall" down into the boiler and this will "pull" hot water from the boiler up to the group, establishing the thermosyphon action.

nirdvorai wrote:The attach draw is from and old post, here on HB, on Londinium 1-P by erics.
Can I assume that the Ater Family water flow to the group is the same?

Yes. I would assume the same basic water path.

Cheers!

- Jake

October 15th, 2020, 10:22 am

I learned something new today

thanks!

To affirm this, when I blow air through each pipe in the group head, in both cases the air come out from the pinhole in the piston chamber.

October 15th, 2020, 10:30 am

Only one outlet in the sleeve/chamber?

October 15th, 2020, 10:58 am

Best to my knowledge this is the only outlet I found:

#9: Post by **Jake_G** » October 15th, 2020, 11:11 am

That is surprising.

I would expect at least 2, if not 3 or 4 with a spring lever. I guess it isn't a given, though.

October 15th, 2020, 11:19 am

How many the Londinium 1-P has?

What is the benefits from multiple outlets?