Posted Thu Aug 16, 2007, 2:20pm Subject: Is anyone using voltage to control Vibe pump pressure instead of OPV?
I've read alot on the forum about how the 15-16 bar vibe pumps can make it difficult to pull a good shot because the pressure is too high without some form of regulation. The most commonly used approach is to use the Over Pressure Valve to bleed off excess pressure above 9-10 bar. A good machine with a decent OPV seems to work well with this approach but a bunch of machines (ie: my Gaggia Espresso) either has no OPV or the design in many cases is intended for a safety release to prevent damage only and regular use is likely to result in a leaky OPV (unless upgraded to a better quality).
I had come across a discussion some time ago about using a Variac to regulate the Vibe pump pressure/output and it occurred to me that perhaps, after characterizing the pump/pressure/volume behavior on a specific machine using a variac to contol the pump, you could install an appropriate resister inline to the pump and achieve the voltage drop to get the volume/pressure drop needed.
While this approach would still be sensitive to shot volume ( would change pressure for single vs. double) it would not be an issue for me (it's double or nothing). Also it would seem you could arrive at a better compromise between singles and doubles than what is delivered with a 16bar pump running full open....
Anyway, I'm curious if anyone has tried this approach and could help me save time in investigating behavior of the vibe pump at various voltages other than 120V? My searches here have not turned up anything.
As a side note, I noticed the pump in the Gaggia is rated for 110V 50-60hz while my line delivers a full 120 across the terminals.
PaulTheRoaster Senior Member Joined: 2 Aug 2005 Posts: 341 Location: Champaign, Illinois, USA Expertise: I live coffee
Espresso: Faema C84 A/1, Eterna leva... Grinder: Compak K6, Solis Classic Drip: French Press, Swiss Gold... Roaster: RK drum
Posted Thu Aug 16, 2007, 3:29pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
If you do a google search for "variac vibe pump" there are a few places where people report success with that.
Calculating the right resistance value will be a little tricky. A vibe pump is an electromagnet and a diode. I am not sure if there is a good way to measure the actual current or power it draws with a regular multimeter. But there might be a few ways around that.
Posted Thu Aug 16, 2007, 5:43pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
Thanks Paul, re: the diode, that explains the extra pump connections and meter readings I got. I gleaned enough from my searches for proof of concept so full speed ahead I went through my parts bin and found a 10ohm 10 watt resistor and stuck it in there: voltage across the pump dropped from 120 to 110 volts. (what luck for seat of pants!) I have no way to check actual pressure on this thing yet. I will give it a couple days running (I know this machine too well by now) to see how it effects shot pour and taste. The pump is just a bit quieter too. I was mistaken on the pump spec: it says "110/120V 60Hz 55 watts" so I'm still within operating spec and should not be dissipating too much current through the resistor.
Tex Senior Member Joined: 27 Apr 2006 Posts: 840 Location: Texas - That's God's country to everyone else! Expertise: Professional
Espresso: Bunn ES-1A (PID'd), Gaggia... Grinder: Rancilio MD50 Vac Pot: Way too many vintage Silex... Drip: Melitta Clarity Roaster: TurboCrazy &...
Posted Fri Aug 17, 2007, 9:34am Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
OK, I acknowledge up front that I'm the last person that should ever say this, but why are you attacking a pressure problem by reducing the pump's capacity? It's a straight forward proposition to install a Gaggia Classic OPV in your Espresso for ~$20. Is there a particular reason for attacking the problem via the pump?
Posted Fri Aug 17, 2007, 2:34pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
In a word Tex: K.I.S.S. Yeah, I read that thread about retrofitting the OPV. I almost get simple and straighforward out of it. Just a few complications. Is there someone that has that valve in stock now? I can't put the machine out of commission until at least monday when I get a Venus. Gotta have the morning Capp. I will be stripping down the Gaggia after the Venus is on line. I have to peek in the boiler to see how much bigger it has gotten with all those little black chunks it's been blowing. I may look at doing something different about the overpressure situation then... or I may loose interest from using the Venus.
I did get a noticable improvement in the morning shots just dropping the voltage from 120 to 110 though. It took me all of about 20 minutes of risk free, no leak modifications to try it. As Jim suggests I do need to get a reading on pressure though to know what I'm doing, but one thing is for sure: it is a step in the right direction.
Tex Senior Member Joined: 27 Apr 2006 Posts: 840 Location: Texas - That's God's country to everyone else! Expertise: Professional
Espresso: Bunn ES-1A (PID'd), Gaggia... Grinder: Rancilio MD50 Vac Pot: Way too many vintage Silex... Drip: Melitta Clarity Roaster: TurboCrazy &...
Posted Fri Aug 17, 2007, 2:49pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
Frost Said:
In a word Tex: K.I.S.S. Yeah, I read that thread about retrofitting the OPV. I almost get simple and straighforward out of it. Just a few complications. Is there someone that has that valve in stock now? I can't put the machine out of commission until at least monday when I get a Venus. Gotta have the morning Capp. I will be stripping down the Gaggia after the Venus is on line. I have to peek in the boiler to see how much bigger it has gotten with all those little black chunks it's been blowing. I may look at doing something different about the overpressure situation then... or I may loose interest from using the Venus.
I did get a noticable improvement in the morning shots just dropping the voltage from 120 to 110 though. It took me all of about 20 minutes of risk free, no leak modifications to try it. As Jim suggests I do need to get a reading on pressure though to know what I'm doing, but one thing is for sure: it is a step in the right direction.
Firm believer in the K.I.S.S. principle myself - not a bad place to start from. However you get there, the pressure does need regulating in the Gaggia. I'd never considered doing it your way, but if it doesn't harm the pump in any way it sounds like a simple enough solution.
BTW: the OPV was available from an Italian source via eBay. Check with Susan (SJM) for more details.
Posted Fri Aug 17, 2007, 4:19pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
Thanks for the link Susan. Did you get yours installed ok? For $49 I think I'll hold out for a domestic supplier or continue with the 50 cent voltage drop resistor approach. Gaggia is about doing it on a low budget and this thing might be asking me for a $50 boiler when I open it up.... hoping I can just clean it up and replace the gaskets.... getting a slightly larger boiler out of the deal ;^)
Okay, okay, my Achilles heel: finishing projects I start. Blush. It's still sitting in the drawer waiting for me to find out where my get-up-and-go got-up-and-went to.
BUT, Prav did get his installed, and you can see how pleased he was with the results if you check towards the end of this thread:
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