How to adjust brew pressure of rotary pump espresso machine? - Page 2

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benm5678

#11: Post by benm5678 »

Hi,

George - i'm curious, when u put on that PF gauge did it rise gradually?

since the internal gauge jumps very quick on my Duetto (unlike videos i've seen of other machines)...

Jeepin' Geo

#12: Post by Jeepin' Geo » replying to benm5678 »

Ben,

Yes, the PF gauge does rise slowly (showing the pre-infusion ramp) compared to the internal gauge.

George

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akallio

#13: Post by akallio »

As far as I've understood it, the internal gauge shows the pressure between pump and gicleur. It will jump very quickly.

If you use blind filter, I think you should see small and slow pressure ramp up after a while when the boiler heats the static mass of water between pump backflow valve and blind filter.

The conclusion might be that internal gauges are good for diagnosing the machine, but not for diagnosing the shot.

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benm5678

#14: Post by benm5678 »

thanks guys, this makes me feel better that it's not reflecting the pressure ramp on the puck. i looked at Brewtus III internal pics and i see now why its videos show pressure rising slowly and reflects more of the group pressure -- it seems to be hooked up to the top of the brew boiler right before the exit to the e61.

i've noticed too when i put the blind in the duetto and run the pump, after about 10 sec, the pressure goes from 9 to 9.5 - 10 (so heat expansion explains it - cool). But i'm still confused why it doesn't jump up to ~12bar (that's the OPV limit, right?). With the blind in, water has no place to go... so shouldn't the pressure build up enough until the OPV kicks in?

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HB
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#15: Post by HB »

benm5678 wrote:But i'm still confused why it doesn't jump up to ~12bar (that's the OPV limit, right?). With the blind in, water has no place to go... so shouldn't the pressure build up enough until the OPV kicks in?
Rotary pumps don't use the OPV to regulate the pressure since they have their own bypass valve. The OPV (properly called an expansion valve in this case) is regulated to ~12 bar to protect the hydraulics system from excessive pressure during machine warmup or in the event of a pump bypass valve failure.
Dan Kehn

akallio

#16: Post by akallio »

benm5678 wrote:thanks guys, this makes me feel better that it's not reflecting the pressure ramp on the puck. i looked at Brewtus III internal pics and i see now why its videos show pressure rising slowly and reflects more of the group pressure -- it seems to be hooked up to the top of the brew boiler right before the exit to the e61.
Are you talking about the rotary or vibe model? I don't see why there should be that big a difference. Of course the vibe model will have a short ramp up due to pump.
benm5678 wrote:thanks guys, this makes me feel better that it's not reflecting the pressure ramp on the
i've noticed too when i put the blind in the duetto and run the pump, after about 10 sec, the pressure goes from 9 to 9.5 - 10 (so heat expansion explains it - cool). But i'm still confused why it doesn't jump up to ~12bar (that's the OPV limit, right?). With the blind in, water has no place to go... so shouldn't the pressure build up enough until the OPV kicks in?
As HB replied, OPV is not used to control brew pressure on rotary machines. A rotary pump is capable of controlling the output pressure by itself.

The pump will pump water until a pressure of 9 bar (or whatever it is set to) is reached. After that it will only circulate water through the by-pass. Now water in the boiler starts to warm and expand. But it will not flow back through the pump, because there is a backflow valve before to pump to prevent that. So what we have is water trapped between the closed backflow valve and the blind filter. It will expand a bit as boiler element heats it, but not indefinitely because heat is cut off when it is warm enough and maintained there. Because the pressure is over the set brew pressure, pump will not introduce new water into the system.

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benm5678

#17: Post by benm5678 »

Ahh.... cool, now i fully understand -- thanks again! :D