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Grimac Mini/La Uno low brew pressure, first plumbed in machine
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benpiff
Senior Member
benpiff
Joined: 5 Feb 2010
Posts: 295
Location: Portland, OR
Expertise: I live coffee

Espresso: RocketR58,GrimacMini,Elli
Grinder: LSM FK Conical, Vario
Roaster: Sonofresco 1lb, Behmor
Posted Sun Apr 7, 2013, 11:12pm
Subject: Grimac Mini/La Uno low brew pressure, first plumbed in machine
 

Hi guys,

I didn't get to test this machine before I bought it, but when I first got it T'd into my sink's cold water line and turned it on, I was able to get water out of the group and everything heats normally. But before pulling a shot, I used my portafilter gauge with needle valve to check brew pressure. The pressure seems to build very slowly, not get above maybe 2-3 bar, and make the machine get very noisy.

The first thing I experimented with was adjusting the OPV tighter, which made the pump louder, the pressure go up a bit (but never past maybe 3 bar), and noticeably less water come through the 3 way valve.

What else should I check? There is a rubber line that runs to the drip tray from another junction box and never see water flow into it (this person has a good photo of it Click Here (s756.photobucket.com)), do you know if this is an expansion valve for the heat exchanger, or is this an OPV (the OPV after the pump just loops back into the line before the pump)? Is my water line pressure the next culprit? I know calibrating the two pressures could be a unique setup for me, so if anyone can email me directly to explain the process for this machine, you'd be a hero!

Edit: I've read a couple different threads that showed people opening up the expansion/OPV valve, and also discussing scale buildup. I definitely have been more distracted by the plumbing aspect than possible scale, so I took out the of the E61 to check the mushroom and gicleur, both looked really good. I removed the expansion valve and there was some murky water in there, but running the pump for a second cleaned that up. I can't get any water to flow through the expansion valve whether it's loose or tight, and adjusting the OPV by the pump still doesn't result in the pressure getting beyond 4 bar in 30 seconds. How long should it take to fill a 2oz shot glass around 9 bar of brew pressure?

Edit 2: I've now done a Cafiza backflush, fully descaled the machine, opened and checked the OPV. It still takes about 25 seconds to fill my 2oz shotglass. Is it most likely the pump or the path to the group?

 
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benpiff
Senior Member
benpiff
Joined: 5 Feb 2010
Posts: 295
Location: Portland, OR
Expertise: I live coffee

Espresso: RocketR58,GrimacMini,Elli
Grinder: LSM FK Conical, Vario
Roaster: Sonofresco 1lb, Behmor
Posted Sun Mar 2, 2014, 1:27pm
Subject: Re: Grimac La Uno low brew pressure, first plumbed in machine
 

Bump, I replaced the Fluid-o-tech pump and removed/checked a few fittings between the pump and the machine, but I don't know why my flow rate is still too slow? I took the e61 apart, descaled and cleaned everything. Does anyone have  any tips for other things I could check? Or do I just need to keep proceeding through pipes and fittings looking for a blockage? Also, what's a minimum diameter for the plumbing lines? I think it came with 1/4 inch.

 
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JY
Senior Member
JY
Joined: 2 Jun 2011
Posts: 27
Location: Washington DC
Expertise: I live coffee

Espresso: Grimac Mini, Pavoni P/Tre,
Grinder: Preciso, Cunill Brasil,...
Vac Pot: Yama, Cory, Rasotherm
Drip: V-60, Clever, Brazen
Roaster: Behmor
Posted Sun Mar 2, 2014, 3:11pm
Subject: Re: Grimac Mini/La Uno low brew pressure, first plumbed in machine
 

My Uno's not plumbed, so I don't have the same setup, but have you checked the pressure before the pump?

After the pump, the water goes to the square brass distribution block where it can either go to the hot water pipe through the solenoid on the side, or to flow meter, and on to the HX. The pressure valve on the end of the block has the silicone pipe that in my machine goes back to the water reservoir.  

After that it's to the boiler, into the injector pipe, and to the group.

You seem to have descaled and checked the entire path. Have you checked the water level in the boiler? If water is passing through to the group, the only other place you might be losing pressure would be through the HX into the boiler.

Hopefully that's not the case.

I would go through the distribution block again. If you check out the blow up on the parts list, there are a few parts in there that could be sticking.

http://www.partsguru.com/user/MINIGRIMAC_LAUNO%5B1%5D.pdf

I also ended up changing the valve with one from Chris'Coffee, which made it much more accurate and easier to adjust:

Click Here (www.chriscoffee.com)

Hope this helps!

JY: IMAG0018.jpg
(Click for larger image)
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