Ahoy!

I decided to upgrade my vibe pump Bezzera Strega to a gear pump with flow control without any coding. This mod will work for any machine with a vibe pump, and can be done for any rotary pump as well with the addition of an OPV valve. I'll order this thread in terms of the components. This isn't meant to be step by step but if you know anything about wiring it should be quite simple.

DISCLAIMER I am not an engineer, electrician, plumber, or have any certifications or professional work experience relating to the mods in this thread. Please check with an electrician before you do any of this. You could fry your machine, or electrocute yourself or anyone in your home. You probably are tossing your warranty as well, although the pump mod is 100% reversible apart from two slightly enlarged holes on the bottom of the machine to run the power cord and trim potentiometer.


Flowrate in ml/s matches the dial numbers perfectly. Enclosure attached to the frame clear via magnets and clear of the drip tray. Yes, the case fits on with no issues but I'm keeping it off for a few more days.

A. ELECTRICAL - I treated this like a boat installation. Using either heat shrink crimp connectors everywhere or marine grade Anchor tinned copper connectors. Few or zero simple soldered connections. They aren't allowed on boats since a solder joint doesn't hold up to heat and vibration. You will also need a 3 wire 18g wire and relief fitting to run from the machine to the control box if you are going to use an external control box like me.


Power Supply 24VDC: Mean Well LPVL-150-24 ~$40

The Brushless DC Pump (BLDC) uses 24V. It can draw 4amps, and never more than 5 amps. This is 100W. A 120W power supply would also work, but according to the temperature chart for the power supply it was better to be safe with a higher powered power supply. Mount the power supply somewhere it will not get too hot. I built a simple bracket out of aluminum. One great thing about this power supply is that it will output a constant voltage regardless of dips of the input voltage - this solves an issue I had with my dimmer controlled vibe pump which would fluctuate significantly if the boiler heater went on during a shot (it always did).

Wiring the power supply is simple. The 120V AC power goes into one side. Jump your cables from the output on your power switch so it's only powered when the machine is on. The output of the power supply negative should go to 1) pump negative, 2) trim potentiometer, and 3) main potentiometer. The output of the positive will simply run to the common terminal on the relay. You don't want to switch the 120V side of this power supply because there is a multi-second delay before power comes on and that wouldn't be acceptable.




Relay SPDT 120V 30A: Auberins model R30A ~$10

The relay turns on and off the pump. All the brains of you machine tell the pump to run to fill the boilers, make espresso, etc. just run power to the 120V cables going to your old pump. We will just use this relay to turn those wires into a switch that will send the (+) 24VDC to the pump. This relay is water proof, and has drain slots if any water sprays on it.

Take your 120V wires that went to your old pump and wire them to the "coil" of the relay. This will close (turn on) the circuit when supplied with power. Take your +24VDC from the power supply and wire it to the "COM" port on the relay. Then make a connector with the 1) + Pump, 2) +24 Trim potentiometer and attach it to the "NO" spade of the relay. The "NC" spade will be loft alone.

The "NO" means "normally open" and, absent any 120V power, will remain open - i.e. no power between the COM and pump/potentiometer. When your machine calls for the pump the 120V will trip the relay and connect the 24VDC power to the pump and potentiometer. The pump has a 65ms startup time, which is about the average reaction time of a cat - good enough for me. You could wire the pump with power all the time and have the relay control the potentiometer only but I feel its safer and better for the pump to only have power when called for.




Potentiometers: Two potentiometers are used to control the 24V signal from the power supply and turn it into a 0-5V signal for the pump controller. The pump has it's own BLDC digital controller. Powering it with a signal from 0-5V (pump will start at .3v) will run the pump at a lineal speed relative to the voltage from 300-5000rpm. Use good potentiometers and get a good linear response.

i. Trim Potentiometer: IPAmerica MT22-10 R100K ~$36
I used a 100K Ohm potentiometer (thanks Jake!) to cut the 24vDC to the max pump flowcrate I wanted below 5V. This is a 10 turn potentiometer with .25% linearity error and will be set once and forgotten. You would use one of this square trim pots, but I couldn't find a high quality one.
Wire the positive to the output of the relay, and the negative to the negative of the power supply at the pump connection. The output of this trim potentiometer will go to the positive of the main potentiometer.
I couldn't fit this in my control box, so I mounted it in the machine with no dial, so I didn't accidentally hit it.

ii. Main Potentiometer: R25W-SRCWT-5K ~$16
This potentiometer rotates 270 degrees and will be the main controller to adjust the pump speed during shots.
Wire the positive to the output of the trim potentiometer, the negative to the 24VDC negative/pump negative, or daisychain it from the trim pot negative.
Wire the output of this to the ORANGE from the pump ("SPEED_IN").

Pump: Fluid-o-tech FG309XD0PV1000 Brushless DC aka "FG309". ~$600 new (mine was $95 shipped from eBay israel).
This pump is in the FG series which means the form factor is smaller than the MG series and a few other differences. Honestly, I'm not sure about every difference except for two big ones.

First, this pump comes with its own controller mounted on the back. Brushless DC motors need a controller to operate, unlike rotary or vibe pumps that run off AC power. This is why we use them for speed control and why you see them on grinders with variable speed. The other MG204/209 series used in some other folks' builds require a third party controller that resemble power supplies and requires an additional dry and cool mounting point. This model has that attached in a very small form factor, so two birds with one stone in my opinion - although it's more expensive purchased new.

Second, the "09" in the name is the size of the gear set. The pump comes with either 4mm, 9mm, or 13mm gears, all with their own flow rates. I was told by FoT that to change the gears you essentially have to buy a new head for the pump for +$300. The 9mm gears have a FAST FLOWRATE, way faster than you would ever need, like 30ml/s. In other threads people mention that the pressure shouldn't rise to unsafe levels using the 9mm gears, but it may with the 4mm gears, so they are a bit safer. My pump will not reliably run below 2ml/s. With the 4mm set, you should be able to easily hit 1ml/s or maybe .8ml/s. If you want to pre infuse down there, go for the 4mm pump.

If you are swapping a vibe pump I belive you don't need any pressure relief valve for the pump since you already have an OPV valve on you machine that should be set to around 10 bar or so which is safe for the pump. Rotary pumps, however, use a bypass valve built into the pump. When you remove the rotary pump and replace it with a gear pump you will need an OPV or some other sort of relief valve to relive the pressure in case it builds too high for your machine and for the pump itself. I think some of these pumps come with this valve already. Lastly, I also heard the model with the o-rings has fewer leaking issues than the PTFE sealed pump.




Tachometer: (OPTIONAL) Auberins ASL-41 ~$41.

I used this to calibrate the pump. Wire it to +/-24VDC and run the Yellow (TACHO) to the "in" of the tachometer. Run the Brown (0V) to the "COM" on the tachometer. This will give you a hz runout on the tachometer of the motor speed. You can go into settings and change the "b" setting to "6" or "60", can't remember!. This is because the pump outputs .6ml/rotation. Configure the decimals and A value to get a readout of ml/s for the pump, i.e. "2.4" for 2.4ml/s. Build this tachometer into an enclosure, or just use it for setup, or don't do it at all! I chose not to for reasons in the "SETUP" section below.

B PLUMBING:

To connect the pump, take out the old pump and make a bracket. My pump conveniently came with a machines aluminum bracket which I used existing holes to mount. The outlet of an ulka pump is 1/8" BSSP female. The inlet is ... a barb? I used McMaster Carr and ended up paying way too much for my fittings, o well. Use teflon tape everywhere except compression fittings.




In order from machine -> Pump -> Water supply

i. 1/8 BSPP Female x 1/8 NPT Male Adapter (McMaster 4822T76) $20
The outlet of an ulka pump and the strega plastic water intake compression tube fitting is 1/8" BSSP female. Connect this to the plastic water intake tube and to the check valve.
ii. Brass Threaded Check Valve with Brass Piston, 1/8 NPT Male x NPT Female (McMaster 7768K25) $14
The gear pump needs a check valve straight away- threat this into the pump outlet.
iii. Next is the pump with 1/8" NPT female fittings in the stainless pump body.
iv. Use the original 1/8" NPT male Tee fitting fitting that comes with the Strega. To be able to thread it into the pump with the bracket I needed a straight 1/8" male - 1/8" female extender.

Old Pump Outlet, just keep the Tee.


C ENCLOSURE: Hammond 1590LB powder coated white ~$5. I used rare earth magnets which STRONGLY hold it to the steel frame of the strega and 1/2" off the counter, without interfering with the drop tray going in and out at all.

D SETUP: Unplug your negative lead to the heating elements in the strega (or other HX machine) and turn it on. This is because the HX throws off the pump rate since it creates pressure by continually boiling water and will make calibration extremely difficult (trust me).

Turn up the main potentiometer all the way. Turn down the trim potentiometer all the way. Run your pump in the usual manner (pull down lever). Use a multimeter to check the output of the trim pot as you turn it up. Stop before 5V. Stop the pump. Make a mark or a note so you never turn the pot higher than that (and fry the pump controller with over voltage).

The next step will change based on how you use the pump. You can run a blind basked in a non/lever machine and see how high the pressure gets, turning down the trim pot until you are as high as you would ever go. Check the flowrate and make sure it's good as well (it will probably be plenty high).

Alternatively, if you only use the pump for pre infusion like me, you can note the number on the main potentiometer when the pump is at max power. On mine that would be "9". Turn the trim pot down until you get 9ml/s. (To get flowcrate check with the tachometer or weight 10s of water three times to get your flow rate. To do that, run the pump and wait for the water to be steady, then use a taped container under the water with a timer to see how much water you got. Divide by 10 and you have your ml/s.)

Since the pump is digitally controlled and you have high precision linear potentiometers you have now calibrated the potentiometers to give you the flowcrate displayed by the number on the front of your main potentiometer knob!!! No need for a tachometer any more.

E USE: To use the pump, simply start a shot and adjust the power to your desired flowrate. You may need to go slightly higher than 2 and then back down to get the pump to start. I find 2ml/s is the lowest I can go with the pump running. At 2ml/s the strega takes about 45s to show drops under the pf, I think that's pretty good. Anything below 2 (.3v) the pump will cut off (with no damage) and you can use this to maintain a low pressure, naturally dwell, or "bloom" the shot. The 4mm gears would easily to 1ml/s. You MUST NOT forget to turn the pump back up after your shot. This is so the machine can fill the boilers when you aren't around, otherwise it may run the pump continuously at too low a pressure to overcome the boiler pressure.



F FINAL THOUGHTS: I'm pleased with the upgrade. The gear pump is quieter than I expected. It gives a more confidant sound than a vibe pump. The beefy power supply and solid stainless construction are appreciated over the ulka. I'm doing a temperature study of the strega to see if I can do full pump shots and all sorts of new-style variable flow-rate espressos. Even if I can't it was a fun upgrade and only cost about $250. I will take the upgrade to my next machine as well! One thing to note is that others who have done this have also installed a needle valve to slow the flow down. I'm on the fence about this, since I think 2ml/s is close enough to low flow that I don't need that and I can simply turn off the pump by going below "2" on the dial and wait.

You can adapt this to a paddle machine by simply using a 5kOHM potentiometer or linear potentiometer attached somehow to the paddle. You would add a second relay so that normally the main potentiometer is bypassed with the paddle closed (otherwise the boilers would never fill), but with the paddle in use the pump would be controlled with the paddle potentiometer.

Also, you want a brew pressure gauge for this. I put one on my Strega using Swagelok fittings to tee the brew tube and put a hole where there was already a cutout in the steel case back.

Pressure gauge tee and serpentine stainless tubing.

Final final thought - I removed the inner spring of my strega the other day and the jury is still out on that one. It was quite easy, although you need to unscrew the wires for the brew switch. You can unscrew (ON MY MACHINE AT LEAST) the shaft by hand. If it's unscrewing from the top threads instead of the piston threads, it will not explode when you get to the end, but gently pop off (aim it at the couch). Test it after three rotations by pushing down on the spring. If you can easily do that, it will be fine. Remove the inner spring. Assembly is opposite.

Other threads that were useful.

Linea Mini EMP Mod (using CoffeeMachinist's mod with the expensive and rare BLDC rotary pump from FoT): La Marzocco Linea Mini EMP Mod
Linea Mini Mod: La Marzocco Linea Mini shot timer, automatic backflushing and flow profiling mods
Chimera Mod: GS/3 Mod EP "Chimera" - a fully configurable profiling mod for La Marzocco GS/3 AV
My question about this: Simplest manual gear pump pressure/flow implementation?
OG Super Strega Thread: The Super Strega: Modifying preinfusion pressures and other functional improvements
Latest Cool Strega Mods: Bezzera Strega mods
PID Strega Grouphead: [url=/lever ... to cool it[/url]

Shoutout to Jake_G and Peppersass for all their helpful comments on HB about flow profiling and gear pumps.

And last, a reality check that although it was relatively simple, my kitchen was a mess for a long time (torch was not used )