Gear Pump Swap Guide for Most Espresso Machines - Page 2

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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bostonbuzz (original poster)

#11: Post by bostonbuzz (original poster) »

You're way past my understanding as I mentioned in the title and my post I made this guide for non coders!

Interesting what you say about the tech output and the Flowrate. I found that testing by weighing water out the group that the tach is accurate since every revolution is equal to .x mls of output. So you just use the correct multiplier to the tach output (which you can do with the auberins tach) and you're set. What does your data show?
LMWDP #353

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#12: Post by elromulous »

tangent: where are folks sourcing these pumps from? I've been scouring the internets for a fluid-o-tech MG304 for weeks to no avail.

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bostonbuzz (original poster)

#13: Post by bostonbuzz (original poster) »

Eeee-bay. I just did a search and found many for $300+ and 4 for 75-99$ used. Do a wide search and look up the pump on FoT's website to see if the specs will work and if it comes with a built-in controller.
LMWDP #353


#14: Post by rosso »

There is some variety on ebay but quite a few available. I bought one last week from israel for $94 incl fedex.

I was not sure if this is the noise that others are experiencing or if my well used unit is a bit worse for wear.


#15: Post by rybat »

Here I am with a new ulka ex5 waiting to go into my machine and now I'm contemplating a gear drive pump.... :shock: :twisted: :mrgreen:

After some more time, what's the take away on the mod? Worth it?


#16: Post by NelisB »

Question: if you want to control flow with a pump, does it have to be a gear pump? Or can a vane pump (with the right motor) also be used to do flow profiling?

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Team HB

#17: Post by Jake_G replying to NelisB »

If it is sized quite small and has a high rpm range, then yes. The 24V Procon vane pump in the Londinium R24 is a good example of this. With the larger pumps and lower speeds, there is a practical limit to how low you can turn the pump before the vanes fail to seal against the housing, and you've got the issue that they are bypassing LOTS of water across their bypass at typical motor speeds, thus control of pressure does not kick in until the bypass is closed, which is at a hilariously low flow rate compared to the rated pump output.

If you look up the old TMFR thread posted by Shadowfax back in the day ('Pressure Profiling' With The Fluid-O-Tech TMFR Pump - Or, Wholesale Copying Greg Scace's Ideas), Greg Scace gets into this a bit, and you can see how Nicholas tackled this.

The TLDR is that if you take a typical espresso flow rate of 2ml/s average, that's 120ml/min and 7.2 L/hr.

The pump in my GS/3 is 70 L/hr.
The puck will generate 9 bar of back pressure at 7.2L/hr, which means the bypass is open until that point.
So if you have a motor speed control that goes from 0 to 10, you have full pressure at the puck until you get the knob down to 1.1 on the scale. And then, you have the issue of the pump going so slowly between 0 and 1.1 that the vanes may not stay loaded and the whole thing fails to do anything useful at all. So the entire range from 1.2 to 10 is useless, and you have really poor control (if any) from 0 to 1.1. Not a great solution.

Nicholas drilled out the bypass so that the pump is always bleeding pressure past the bypass. This way you keep the motor RPM high, and the pump acts like a really inefficient pump that is much smaller than it really is. But, it gets you a linear response between pressure and motor speed.

Hope this helps.


- Jake
LMWDP #704


#18: Post by NelisB »

Thanks a lot Jake! That's really helpful info.