Another Breville Dual Boiler flow control mod.

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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#1: Post by lancealot »

Hello Coffee Community!

I am writing this to share the mod that I have been using for flow control of my BDB. This mod is a tweak on an old mod. In order to help the reader understand what I mean, I will offer a brief history of flow control mods on this machine.

A Brief History of Flow Control Mods on the BDB
1.) Soon after this machine hit the streets, keen users learned that they could reduce the flow to the puck by opening the water valve. Care was needed in this because if the valve was opened too far, the micro switch was triggered and the extraction was terminated. It was learned that some machines would allow you to open the valve more than other machines due to manufacturing inconsistencies. If you got one with sloppy tolerances, you were a winner!
1.a) It was not long before someone opened the machine and took out the microswitch that was responsible for cutting the shot when the valve was opened too far. This allowed the operator to open the water valve however they liked and the extraction would not be stopped. In both of these mods, the water that was diverted through the water valve, exited the hot water spigot and went to the drip tray resulting in water wastage.
2.) The Slayer Mod. Jake and Peter ( Jake_G & pcrussell50 ) developed the current de rigueur profiling mod. of re routing the tubes so that the hot water valve acts as a throttle, controlling the flow to the puck. In this mod. the OPV acts to dump the excess water back to the tank so that there is no water wastage. A very elegant solution, it provides flow control throughout the shot, wastes no water, costs no money and results in no damage to the machine, making it completely reversible.

Mod 1.b. (the mod I use now).
I pull mostly medium roast coffees and have found that for my taste, the declining pressure profile associated with lever extractions has the most positive impact on the coffee I make. I have had my machine in configurations 1.a and 2 for several months each. Working with the stock Breville hot water valve, I have found it more intuitive to execute the declining pressure profile that I prefer by controlling the flow with the valve as it is operated in Mod 1 and 1.a. In these mods, full pressure is achieved with the valve all the way closed, and to reduce the flow, you crack the valve. In mod. 2. full pressure is achieved with the valve all the way open and to reduce the pressure, the valve has to travel to the point where it is almost closed. I found this harder to control, less intuitive and less repeatable - for me. Mod 2 does offer significant advantages to mods 1 and 1.a if you want fine flow control at the beginning of the shot. Mods 1.b and 2 both have the advantage of not wasting water.

Several months ago, I switched my machine back from mod 2. to mod 1.a. because I found it more intuitive for me to control. However I was frustrated that so much of my good water was going to the drip tray. So I set out to find a way to route the hot water waste back to the tank. After thinking about drilling and melting and all kinds of fabrication tactics I opened up the machine to have a look. I found, as we BDB moders have so many times, that the BDB is almost made with a solution for this mod in mind.

Mod 1.b. How to...
In the deck above the water tank there is a port that leads directly to the tank below. I removed the hot water (tea water) line from the hot water spigot at the spigot. Then secured the end of the hot water line that used to enter the spigot, in the port in the deck above the water tank using a zip tie. I knew I would have to secure this very well or I will end up with water all over the inside of my machine. I also had to ensure that the water line was not inserted so far into the port that I would not be able to remove the water tank. Next, there is a micro switch above the water knob. You have to prevent the switch from engaging with the hot water knob so that opening the water valve does not trip the switch and stop the shot. It's easy. Undo the 2 Phillips head screws that secure the micro switch to the machine chassis. Pull the switch out of its mount and set it further inside the machine, in a place where the switch won't be disturbed. There is plenty of room inside the machine to find a nice place for the switch to live.

Closing Thoughts
I have been running my machine like this for several months. I did not post about it at first because I did not want to end up with water all over the place and have to reply to my own post that this was a disaster. I am happy to report that this has not happened. This mod is not really anything new. It is a small improvement on mod 1 and 1.a. Comparing it to mod 2., it offers less intuitive flow control over the start of the extraction but more intuitive flow control over the end of the extraction. That said, I have learned to control the flow at the beginning of the extraction when needed and I have also used the programmable preinfusion feature of the BDB to handle flow control over the beginning of the extraction for me. I will not argue that it is better or worse than any of the other mods but I will say that it has worked well for me.

A picture is worth a thousand words. So I give you pictures in addition to all my words :)


Demo Video: Operation overview with blind basket
Demo Video: Lever style shot
(coffee was not dialed in, so the shot flowed real fast! this was just for demo purposes)
Demo Video: Slayer style shot
Note about the videos: the shots pulled in the videos were done with a fairly empty water tank. In some of the videos, if you listen carefully, you can hear the flow of water going back into the tank. You really only hear this when the tank is fairly empty. It is not a disturbing sound at all and it is barely audible with the pump running. I just wanted to point it out and let you know that with more water in the tank, you don't hear it.


#2: Post by pcrussell50 »


Wow Chris. What innovation. If I understand it, that's the GS/3MP, only without having to actually waste the water down the drain. Huge.

LMWDP #553


#3: Post by cccpu »

Chris, is there any way to post a YT video of how pulling a shot works by any chance with your workflow? Those have been very helpful for me at least in understanding how and what the previous mods were doing.
LMWDP #583


#4: Post by IMAWriter »

JUST when I thought I might have this NAILED! :lol:
newbie question: does this mean one MUST use the Breville's control panel to initiate flow...or at least the preinfusion? Forgive my ignorance, as I'm only familiar with things through these wonderful threads..
LMWDP #187

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lancealot (original poster)

#5: Post by lancealot (original poster) »

You start the shot by pushing the buttons on the front of the machine, just like you would under normal operation. You can preinfuse manually, by cracking the valve to control it, or you can use the programmed preinfusion. When you want the pressure in the shot to trail off, you crack the valve open to reduce the flow to the puck thereby reducing the pressure.

I'll take a demo video in the next few days.


#6: Post by luvmy40 »

This is a great solution, if you don't use the hot water spigot. We make quite a few americanos, which is why I haven't done the full Slayer Mod.

What I do is simply place a frothing pitcher under the water spigot and either dump the run off back in the tank if I'm drinking espresso or add it to my americano.


#7: Post by pcrussell50 »

Chris, I added your process to the "mods" section of BDB mods and maintenance:
Peter sez:
On EDIT: Chris/Lancelot has come up with an elegant upgrade to this method, where the water does not get wasted into the drip tray. And it's easy too. Three cheers to Chris. Here is the link to his writeup: Another Breville Dual Boiler flow control mod.
LMWDP #553


#8: Post by breenmachine »

I'm curious how this affects water temperature in the reservoir? Would it increase it enough to be concerned? Ulka pumps are only rated to work with water at about 20C, in most cases water in the reservoir is probably already at or above that temperature.

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lancealot (original poster)

#9: Post by lancealot (original poster) »

Interesting thought. Well, it is def. going to increase the temp of the water in the tank. How much depends on some factors. I don't think it will be an issue under responsible home use. I guess it would be easy to set up a thermocouple in the tank and watch it for a few days. I don't think I am going to do that right now though. Life is crazy and I am not worried about the tank water getting too hot.

If the reservoir is mostly empty, it will have more of an effect than if the tank is mostly full. If you do many, successive, long, low-pressure preinfusions with an irresponsibly low amount if water in the tank then it will increase it a lot. I would not do that.

Me? I am not worried about it. I doubt it is going to be an issue. When I am pull more than 3 shots in a row I am usually in "guest production mode." and I am not flow profiling for guests. I have never seen a steamy reservoir level viewing window on my machine. If i start burning up successive ulkas though, I will start taking the temperature of the water in my tank.

edit: it is remarkable that the max water input temp is 68 F (20 C). Still, I am undeterred. :D

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lancealot (original poster)

#10: Post by lancealot (original poster) »

Videos uploaded at the end of the first post in this thread.