Machine Pumps: Vibration vs. Rotary

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goalerjones

#1: Post by goalerjones »

The 2 kinds I'm remotely familiar with are:
Rotary and
Vibration

I know:
Vibration has shorter life and cannot be used for plumbing machines.

What I don't know:
How each pump actually works?
How cycles are measures in vibration/rotary pumps? Is it from turn on to turn off, or time used in total?

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HB
Admin

#2: Post by HB »

From the FAQs and Favorites for this forum:

How a rotary pump works
How a vibratory pump works

In both type of pumps, the brew time is measured from the time the pump turns on. Because vibratory pumps heat up, their duty cycle is limited (typically 1 minute on, 1 minutes off). Rotary pumps don't have the same limitation.
Dan Kehn

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bluesman

#3: Post by bluesman »

goalerjones wrote:I know: Vibration.........cannot be used for plumbing machines.
But it can. There are many plumbed machines with vibe pumps, e.g. Oscar. A vibe pump won't pass line pressure when off, so you can't use the pressure of the water supply to preinfuse. But that's the only thing it won't do that a rotary will (except lasting for many more years and being easily rebuildable). You just have to replace a dead vibe pump.

goalerjones

#4: Post by goalerjones »

What determines the life of a pump? How many times it's turned on and off, or how long it's used?

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bluesman

#5: Post by bluesman » replying to goalerjones »

"All of the above", plus many more. How it's used is critical, since vibe pumps have a duty cycle below 50%. Running it too long (generally over 60 seconds) will heat it up, so it needs at least as long to cool down before starting up again. Habitually leaving it in for more than a few seconds at full pressure during backflush is unnecessary and hard on it, as is waiting over a minute to see a drop or two from a choking grind.

Ulkas are tough - the same pumps we use power many things, e.g. theatrical fog machines.

okmed

#6: Post by okmed »

bluesman wrote:A vibe pump won't pass line pressure when off, so you can't use the pressure of the water supply to preinfuse.
It will pass line pressure. I have a Strega that uses a vibe pump and have it plumbed in. I installed a switch that removes the pump electrically, this allows me to preinfuse with line pressure. The vibe pump is basically a electrically operated check valve that will allow flow as long as other valves like solenoid valves in the flow path are open. With the Strega, when the lever is pulled down the flow path is opened.

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bluesman

#7: Post by bluesman »

okmed wrote:It will pass line pressure. I have a Strega that uses a vibe pump and have it plumbed in. I installed a switch that removes the pump electrically, this allows me to preinfuse with line pressure. The vibe pump is basically a electrically operated check valve that will allow flow as long as other valves like solenoid valves in the flow path are open. With the Strega, when the lever is pulled down the flow path is opened.
With all due respect, I think you may be making 1 or both of 2 errors: generalizing from the Strega to all vibe pumps, and assuming that your pump is turned off when it's still energized and the piston is withdrawn. First, look at this working animation of an Ulka vibe pump:
Image
The one way check valve is in the outflow port and is spring-loaded to remain closed unless it's being pushed open by pressurized water driven by the pump's piston. There's no solenoid or other opening mechanism on the check valve - it's purely passive (and I can't find an opening pressure spec for it anywhere). But my regulator's set to 25 psi and line water will not pass the pump in my Oscar. I've tried forcing water through other vibe pumps and it will not pass at the maximum pressure I can generate with a 10cc syringe.

Here's a Feb 20, 2014 post by TomC about his modified Strega with a dimmer on the pump:
TomC wrote:Simply stated, on my Strega, with the pump essentially off (it's never completely off, but the flow is so restricted when dialed "off" that it might as well be), my adjustable line pressure provides a very simple, straightforward pre-infusion.
If I understand him correctly, and it's possible that I don't, the pump in his Strega will pass line pressure water when the dimmer he used is dialed all the way down - but the pump is not off. I haven't tried it, but this makes sense if there's enough juice to cycle the pump at all and sufficient current flow to energize the opening solenoid.

The Strega may be plumbed differently from standard pump machines, too. I have a Lutron dimmer on the vibe pump in my Oscar, and line pressure does not flow through when the dimmer is all the way down. The pump makes a clicking noise but there's no flow until I dial it up about halfway, at which point I get about 7 bar at the blind PF, from which point it goes smoothly to 15 at max.

How exactly are you "remov[ing] the pump electrically"? Did you put a SPST switch in the hot wire?

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another_jim
Team HB

#8: Post by another_jim »

okmed wrote:It will pass line pressure. I have a Strega that uses a vibe pump and have it plumbed in. I installed a switch that removes the pump electrically, this allows me to preinfuse with line pressure. The vibe pump is basically a electrically operated check valve that will allow flow as long as other valves like solenoid valves in the flow path are open. With the Strega, when the lever is pulled down the flow path is opened.
Um, the Strega model with both plumb-in and pump has a bypass valve for the pump.
HB wrote:Because vibratory pumps heat up, their duty cycle is limited (typically 1 minute on, 1 minutes off). Rotary pumps don't have the same limitation.
There are some commercial vibe pumps, e.g by Fluid-o-tech, rated for continuous duty. They are or were used only used on blue collar commercial single group machines that never found much traction with home users (e.g. Pavoni Pub, Gaggia TS, Rancilio Class 5). Haven't heard much about them recently, and maybe they've died out due to the smaller rotary units available now.
Jim Schulman

Flitzgordon

#9: Post by Flitzgordon »

I notice that the vibe pumps die easily in the process of descaling.
Not sure if it hit the duty cycle limits or the round ball in the pump had eroded.

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bluesman

#10: Post by bluesman »

another_jim wrote:Um, the Strega model with both plumb-in and pump has a bypass valve for the pump.
Thanks, Jim. I knew there had to be an explanation - I just didn't know what it was. That's why I suggested to okmed that "with all due respect, I think you may be making [an error by] generalizing from the Strega to all vibe pumps...The Strega may be plumbed differently from standard pump machines, too."

The Strega is beautiful - if (OK - when) Oscar dies of natural causes, I'd love to have one!