Convert to rotary pump - stepper motor

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by davsvatos »

I have decided to convert my Rancilio Silvia espresso machine to a rotary pump. My plan is to use a stepper motor so that I can control the speed. Does anyone know what motor I should use to power the pump? Would this motor be sufficient ( ? I have no idea how strong it needs to be and I don't want to go through trial and error :D



#2: Post by nisb »

Rotary vane pumps use bypass valves for pressure control - reducing speed wont help as they likely won't be functional at low speeds (they need centrifugal forces on the vanes unless they are on springs).

If you want flow/pressure control I'd look into gear pumps.


#3: Post by ToM4 »

Hello David

I have a rotary pump and often wondered if it was possible to swap the RPM motor for a smaller one.
I see a few issues/question :

- the power of the pump
- it speed
- the level of noise
- the connection to the pump itself.

I wonder if a 5v pump would give enough force to move the pump that had quite a lot of resistance. As I'm a CAD and mechanics addict I saw this motor on Gobilda : ... v-encoder/

My concern is about the connection to the pump. I wondered if a sturdy 3D printed shaft connector would be tough enough. Theres also the question of the force as I said before. This motor delivers 7,9kg/cm2. As an exemple, with a 120w RPM motor I can reach a 14 bars maximum pressure.
I think I'm going to do a part in 3d to assemble it to a standard procon pump.
Theres also the question of the power converter. Where to place it. IMO easier than tryinng to insert a big rotary motor.

davsvatos (original poster)

#4: Post by davsvatos (original poster) »

Yes, I know that. I wanted to use a stepper motor because it is small and has a lot of power. And I would use the speed setting to adjust the correct speed for the pump to function properly. A standard large motor probably wouldn't fit there.


#5: Post by ToM4 »

In think the Gobilda motor won't have enough torque. I made a quick 3D adaptative part that would fit a small motor shaft.
I guess a stepper motor will be much too slow. You need about 1500 rpm.

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#6: Post by HB »

I know next to nothing about gear pumps or stepper motors, but I've read many threads where someone used a voltage regulator (even a dimmer) to control a vibratory pump's output pressure. Click here for some prior discussions.
Dan Kehn


#7: Post by WWWired »

Hi davsvatros :) Fascinating question and one that I'm sure many folks have thought about :)

A Rotary Vane Pump has a specific interface that consists of a slotted fitting on the electrical motor and matching rectangular fitting on the mated vane pump itself. ToM4 mentions this interface adaptive challenge above. The online seller site listing davsvatros links above in the original posting appears to show a solid shaft (image 1 and image 2, in case the online site removes that listing). It would likely need to be modified to accept the vane pump's fitting and as the video below (from Home-Barista site sponsor 1st-line Equipment) shows in the second half of the video, the assembly also consists of a collar that mates with the electrical motor and a clamping mechanism that secures the vane pump to the electric motor. This is a very secure assembly. There are two sizes of electric motor generally. The one in the video below (credit to 1st-line Equipment once again) is the smaller version of these electric motors but there is one that is slightly larger for higher use machines. As well, not sure if that stepper motor linked above in the original post requires a capacitor to drive it . . . most espresso machine electric motors require a rather large capacitor to energize the electric motor properly. I couldn't find mention in the advertisement listed in the original post above, but often these items online don't mention the supporting components and it may be that despite the listed relatively small size of that stepper motor in the ad, it might still require a coke can sized capacitor to drive it.
davsvatos wrote: . . . I wanted to use a stepper motor because it is small and has a lot of power. And I would use the speed setting to adjust the correct speed for the pump to function properly. A standard large motor probably wouldn't fit there.
If it is anticipated to plumb in, including possible water treatment under-counter, perhaps moving the entire Electric Motor/Rotary Vane Pump assembly under counter as well might solve the considered need for a shoe-horn (I believe what HB/Dan Kehn calls turning an inboard into an outboard).

Rotary Vane Pumps are often said to rotate at about 1500 Rotations Per Minute (RPM) as ToM4 notes above.

Speed, Flow, Pressure . . . altering Resistance in a Hydraulic System
Building on the great insights of nisb above, there are some interesting issues worth considering. Some discussions mention controlling Pressure in a hydraulic system. Other discussions might discuss controlling Flow. Like Pressure and Temperature, in a fixed-volume-pressure-vessel it's possible that in some scenarios Pressure and Flow are two sides of the same coin.

A Rotary Vane Pump has an Adjustment Screw to control the resistance in the entire hydraulic pathway (brew pressure). This can be seen at about 3 minutes into the 1st-line Equipment video below.

Faster or slower electric motor speed might alter the resistance in the hydraulic pathway. Increasing or decreasing the rate through altering motor speed would alter Flow and thus the Pressure (because the area is constant in a fixed volume pressure vessel). What is being changed in a fixed-volume-pressure-vessel is the resistance some might suggest. Adjusting the screw on a Rotary Vane Pump itself likely also alters the flow/pressure (resistance) in the hydraulic system. The adjustment of the speed of an electric motor and the adjustment of a screw on a vane pump appear to have the same effect on resistance in the hydraulic pathway but using different methods. A vane pump would require a screw driver to adjust pressure whereas an electric motor might be controllable using add on electronics. There appear to be advantages to both systems.

I'm not sure if an electronic control for the Adjustment Screw in a Rotary Vane Pump is currently available, but an electronic assembly that adjusts the screw on a vane pump would be indeed very fascinating and have, perhaps, the same effect as the proposed stepper motor driving the Rotary Vane Pump itself . . . and maybe some form of blue tooth or other magical/electronic sorcery could be rigged up to tighten or loosen the Rotary Vane Pump screw haha! Basically a stepper motor that adjusts the Rotary Vane Pump's pressure screw instead of stepper motor that drives the Rotary Vane Pump itself . . . Both systems are very interesting and might involve some need for fabrication unless someone here knows of a system that already does this! Awesome idea/question by davsvatros and the above replies are fantastic reads! ToM4 and HB's posts had me reading and researching for a few hours of fun! Here's the video from 1st-line Equipment for anyone curious about different types of pumps and particularly vane pumps . . . would be fascinating if someone had already developed a blue-tooth controlled stepper-motor control screw for vane pumps! . . . quick someone patent this haha! :)

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#8: Post by Jake_G »

The big issue with trying to control the brew pressure on a rotary vane pump with speed is their flow rate capabilities relative to the flow rates typically required when pulling a shot of espresso. As others have noted, rotary vane pumps turn in the neighborhood of 1500rpm. What was not mentioned was their flow rate and how the bypass valve on the pump deals with that. A good discussion was had around controlling a rotary vane pump in this topic:
Gear Pump Swap Guide for Most Espresso Machines
I'll quote myself to save time:
I wrote: 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 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 the pump volume drops from 70L/hr down to 7.2L/hr.
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.
Empasis and italics added for clarity...

Also, stepper motors don't need a capacitor, they need a stepper motor driver, which can be quite small, but is is generally much more of a "thing" to deal with than a simple start/run capacitor. For a 200W stepper, you're looking at a 2"x4"x6" footprint for the driver.

At any rate, the above issues are in fact real. If you don't want to read the link in the link to see how it was addressed, Greg found that the key was to drill a hole in the bypass plunger big enough that that the bypass leaked even when it was closed. By getting the hole size right, he was able to get the pump to generate 9 bar at max speed, and less pressure as soon as the speed was turned down just a little bit. You basically turn the 70L/hr pump into an 8L/h pump by bypassing 62L/h around the pump, even when the bypass valve is closed. Hardly efficient, but effective.


- Jake
LMWDP #704


#9: Post by ToM4 »

Hello All

I wanted to add an image, is it possible directly? Sorry I'm new on the forum. It's just to show the CAD part.

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#10: Post by Jake_G »

LMWDP #704