Jasonian wrote:Sure, but finding that balance isn't as easy as you might think... even with a PID. How long does it take boiling water to cool a hunk of metal?

All the E61 HXs I've measured idled well below boiling point at the dispersion screen (around 185-195F). The thermal flush is warming the group and cooling the HX. As you said, it would be hard to cool a group idling above brew temperature with boiling water.

Nice work Jon. I'm a bit curious about one thing though. The way I understand it is that you have the HX outlet going into the top of the E61 head, and the bottom (input) of the HX going to the lower fitting. Heat naturally follows a convection cycle through the HX when idling, thus heating the group. But when you start the brew cycle, a valve opens to let cold water into the HX from the bottom, upwards, and out the top, through the restrictor, and out the group. Right? So doesn't the restrictor restrict the flow of water during the brew cycle too or is it big enough not to make a difference? If it did, though, could you achieve the same result by putting the restrictor in the bottom fitting so it wouldn't affect the brew cycle? Just trying to get a better idea of how these things work so I'll know what I'm doing with my Mininova. Thanks,

Jordan

RegulatorJohnson wrote:FWIW i can see them. and it appears you are correct.

thanks again!

jon

McMaster-Carr is a good source of bspp fittings and information as well. They might even have some info on how to tell what size your fittings are. I'd imagine a little searching on BSPP fittings in google might help as well

-Greg

oofnik wrote:The way I understand it is that you have the HX outlet going into the top of the E61 head, and the bottom (input) of the HX going to the lower fitting. Heat naturally follows a convection cycle through the HX when idling, thus heating the group. But when you start the brew cycle, a valve opens to let cold water into the HX from the bottom, upwards, and out the top, through the restrictor, and out the group. Right? So doesn't the restrictor restrict the flow of water during the brew cycle too or is it big enough not to make a difference? If it did, though, could you achieve the same result by putting the restrictor in the bottom fitting so it wouldn't affect the brew cycle? Just trying to get a better idea of how these things work so I'll know what I'm doing with my Mininova. Thanks,

Jordan

The pump outlet is somewhere in the middle of the HX, not the bottom. Brew water is forced from both the top and the bottom of the HX tube, a mixture from the top inlet and the bottom outlet forced in the reverse flow direction. The brew temp depends on the HX water temp, the group temp and the cold water temp. Each machine has a different amount of brass in the group, immersed HX area, cold water temp and pump capacity. Add a few miscellaneous variables and an HX flush is almost as personal as a fingerprint.

Different lengths and styles of cold water injector, along with the flow restrictor, adjust the flush / brew water temperature by adjusting the ratio of hot water at the top of the HX and the cooler water at the bottom.

The bottom outlet on my machine was about 20°F cooler than the inlet with a boiler pressure of 0.9-1.1bar .
Pre PID it ran about 225°F and 205°F.
Post PID the top inlet runs about 209°F, which gives a consistent 200°F±1.5°F brew temp measured in the puck. Not close enough for some, but close enough to allow me to walk up at any time and pull a very tasty shot without a flush.

Hi Ian, thanks for the reply. The heat exchanger design makes a lot more sense now. So basically, the restrictor is just small enough to limit the thermosyphon action but does not affect the pump flow during brewing, right?

oofnik wrote:So basically, the restrictor is just small enough to limit the thermosyphon action but does not affect the pump flow during brewing, right?

I don't know enough about fluid dynamics to definitively say what happens, but I expect it affects both.

Imagine a tube with one end almost sealed. With no backpressure, if you inject water into the middle, more water will come out the end with the larger opening. This is the cooling flush mode and e61 pre-infusion part of the shot.

When there is 10ish bar in the HX, intuition tells me the flow through the restrictor will be close to equal the flow from the bottom as long as the flow through the puck remains considerably below the limits of the restrictor.

I imagine part of the art of espresso machine design is dealing with the fluid dynamics to get repeatable results.

The 2 mm restrictor has zilch effect during brewing - that's a relatively simple "plug and crank" orifice calculation. The key being the AVERAGE flow rate during the brewing process which is about 3 ml per second.

The effect it has on the thermosyphon flow is far more difficult. Do a "google" on "thermosyphon calculations" and you'll see what I mean. Suffice to say that IT WORKS and accomplishes the very goal it was intended.

Eric S.

Gah, thermodynamics... it's crazy stuff.
It makes sense, though. Low flow rate, high pressure, shouldn't affect much during brewing I guess. Interesting stuff. Why don't more machines include an adjustable thermosyphon restrictor like the one in the Faema Legend?

It has been posted a few times on the boards before. I think it's a great idea. You could have yet another dial to tweak in your espresso machine!

oofnik wrote: Why don't more machines include an adjustable thermosyphon restrictor like the one in the Faema Legend?

I fully agree - the idea of walking up to a fully warmed up machine, pulling a shot, maybe making a cappy and then repeating that process either immediately or "x" minutes later should cost less than $4500. Unfortunately, such is not the case . . . yet.

The Faema valve is part of (soldered) the Hx outlet/GH inlet line. I have part numbers for the valve internals, sans body. I don't yet have a p/n for the whole assy but that just means a visit to the local espresso store. I would like to think it is less than $100 but, you never know. There's other possible solutions also - maybe a Swagelok needle valve with three settings - ya know - (1) normal (2) dinner party (3) barista jam

Eric S.

hey WTF? i didnt get ANY of these replies!

oh well.

ok so its been a bit of time and i pushed through a fair amount of coffee using the restrictor from AU.

i can tell you that i am still very very happy with how it turned out. i use WAY less water.

the initial cooling from a idle of longer than 30 minutes is about 6 oz to get the temp to 204° (used to be 8-12oz). then i wil flush while tamping another 2oz before each shot after that. it used to rebound so fast that it would requires 6oz flushes.

i used to refill my external 1.25 gallon tank EVERY DAY! now every THIRD DAY! same shot production less flushing.

i also noticed that the "backflush cooling flush" still works well. i have begun to experiment with a few backfluses to cool the group initially then move to normal flushing between shots. seems to save even more water. i think having an external tank is very handy.

jasonian, you need one of these. i went through the adjustment to find a correct setting that gave me minimal flushing and maximum steam. after much up and down i ended up where i started at the factory setting. i am still at the factory p-stat setting with the restrictor.

oh yeah and eric TC adaptor has really made this machine very user friendly. i have my 10 year old step son pulling great shots on his own. he is also making some great microfoam, got a few apples even. his max tamp pressure is 30lbs i tell him to push as hard as he can.

i wonder if those guys at EX/AU would send a few more to me to share?


rj

-- how come i dont get the replies after the first replies?