jdrock Senior Member Joined: 24 Jan 2011 Posts: 21 Location: HK Expertise: I live coffee
Posted Tue Mar 1, 2011, 8:58am Subject: No Pre-Infusion on Vibiemme Domobar Super
Hi, Just got my Vibiemme Domobar Super with rotary pump and plumbed-in water line. Everytime when I start the brew, the pressure always ramp up immediately to 9.5bar without any delaying or stopping. By watching the Vibiemme Junior, I can see the pressure slowly climbed to 4bar at around 4 seconds then only shot up to 9.5bar quickly. I believe this is the function of pre-infusion on the E-61. To wet the puck at the low pressure following with the full pressure brew. But why is it not happening on my rotary version? Is that the rotary pump has no pre-infusion? Or I didn't notice? Advice needed before I send it back for warranty. Thanks.
jdrock Senior Member Joined: 24 Jan 2011 Posts: 21 Location: HK Expertise: I live coffee
Posted Wed Mar 2, 2011, 1:18am Subject: Re: No Pre-Infusion on Vibiemme Domobar Super
Yes, I have the regulator installed which always maintain 2 - 4 bars of pressure to the pump, that I can see from he brew pressurw guage when the machine is off. I always assume the brewing pressure will go stright to 4 bar and wait for few seocnds before the actual brew pressure. I am confuse now.
Posted Wed Mar 2, 2011, 9:44am Subject: Re: No Pre-Infusion on Vibiemme Domobar Super
If you adjust the pressure regulator on the water supply line does the pressure gauge change? I ask because the gauge on the machine will hold pressure even on reservoir machines when the machine is off. You should have a separate gauge on the supply line before the machine to verify the line pressure going to the machine. And my reservoir, vibratory VBM Domobar Super does go to around 4 bar, sits there for a little while, then ramps to 9.5 to 10 bar on the gauge.
jdrock Senior Member Joined: 24 Jan 2011 Posts: 21 Location: HK Expertise: I live coffee
Posted Wed Mar 2, 2011, 5:57pm Subject: Re: No Pre-Infusion on Vibiemme Domobar Super
OK, here is the setup, instead of directly connect the machine to the direct line water, I use an external 5 gallon water tank. Then I have an external water pump connect to the tank and supply the water to the machine constantly, this is to ensure the rotary pump does not suck the water directly from the tank. I have read from the forum that we should not let the rotary pump sucks the water from the external reservoir. So I am not sure if it is to do with the external water pump or my setup is wrong. What can a pressure regulator helps for the pre-infusion?
Posted Wed Mar 2, 2011, 7:28pm Subject: Re: No Pre-Infusion on Vibiemme Domobar Super
Is the pump that supplies the pressure to the machine connected to go on when the machines rotary pump is activated? How much pressure does the external pump develop? What pump is it? If you use a blind filter (like backflushing) what is the highest pressure the gauge on the machine shows when the brew mode is on? There are a number of experts on homebarista.com (http://www.home-barista.com) with similar setups as yours who will be able to help with the technical issues.
jdrock Senior Member Joined: 24 Jan 2011 Posts: 21 Location: HK Expertise: I live coffee
Posted Wed Mar 2, 2011, 8:08pm Subject: Re: No Pre-Infusion on Vibiemme Domobar Super
Yes, the external pump will always maintain a minimum pressure to the machine, it has a pressure valve to ensure the water line to the rotary pump always filled. I am not sure what brand is that, it is just a small box with inlet (water tank) and outlet (machine) hose. With the blind filter, I can see the pressure goes up to 9bar immediately and stay for 1 second following with a "hssss" sound (which I believe is blind filter full with water), and the pressure will slightly goes up to 9.5bar and maintain it there. Is that "hsss" sound and 1 second pause mean pre-infusion? But is seems to be too fast. With the correct grind size (25 seconds for 25ml), I can see the coffee start dripping out from the bottomless portafilter in around 2-3 seconds, as compare to the Junior which normally takes around 10 seconds to see the coffee.
DavecUK Senior Member Joined: 21 Sep 2005 Posts: 941 Location: UK Expertise: I love coffee
Posted Thu Mar 3, 2011, 7:18am Subject: Re: No Pre-Infusion on Vibiemme Domobar Super
jdrock Said:
Hi, Just got my Vibiemme Domobar Super with rotary pump and plumbed-in water line. Everytime when I start the brew, the pressure always ramp up immediately to 9.5bar without any delaying or stopping. By watching the Vibiemme Junior, I can see the pressure slowly climbed to 4bar at around 4 seconds then only shot up to 9.5bar quickly. I believe this is the function of pre-infusion on the E-61. To wet the puck at the low pressure following with the full pressure brew. But why is it not happening on my rotary version? Is that the rotary pump has no pre-infusion? Or I didn't notice? Advice needed before I send it back for warranty. Thanks.
Absolutely nothing wrong with the machine, it's simply that the pressure take off point will be after the pump and show the immediate rise in pressure from the rotary pump. Only a pressure measuring portafilter will show the rise in 2 stages, preinfusion first, then a rise to full pressure, then a rise beyond the pump pressure as expansion due to the cooler water entering the brew circuit being heated,
The reason the vibe pump machine showed the ramp characteristics it did is due to the much slower flow rate of the vibe when under pressure and as the preinfusion chamber fills the pump registers the lower pressure value, then once it's full jumps to 9 bar (or whatever it's set to). Rotary pump has much higher water flow, so simple the restriction of the gicleur alone is sufficient to give 9 bar pressure even without a blind filter in the group.
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