Brew Pressure Sometimes Gets Very High

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bgour
Cappuccino
Posts: 28
Joined: Sat Jan 24, 2009 2:56 am
Location: Vancouver, British Columbia

Brew Pressure Sometimes Gets Very High

Post by bgour » Sun Feb 03, 2019 3:06 pm

Hi All,

S1V1 (rotary pump)

During the course of some regular maintenance today I noticed an odd behaviour. Checking the brew pressure (with a portafilter pressure gauge) the pressure gets to about 130 psi. Most of the time it remains at that pressure but sometimes after a few seconds stable at 130 psi, the pressure will steadily rise and reach 190 psi (!) if I don't cut it sooner.

Is this normal? It's been there since new but I've never though much of it, rationalizing that this is unlikely in an actual brew scenario. Note that my manometer has no bleed valve to simulate pulling a shot, so perhaps my test is unrealistic? Maybe I should rig a bleed-valve and re-test? Also, does the OPV come into play here?

Many thanks,
Brad
Vivaldi S1 V1, timer
Mazzer Mini

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chas
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Re: Brew Pressure Sometimes Gets Very High

Post by chas » Mon Feb 04, 2019 11:00 am

It sounds like you have two problems:

1) The expansion valve should be adjusted to open at 12bar and dump water into the drip tray so you should never see a group boiler pressure higher than that. This is what prevents the boiler from exploding so you should be sure this is correctly adjusted. (See the manual for instructions.)

2) The pressure adjustment mechanism inside the pump is supposed to prevent the pressure from going above 9bar (or whatever you have sent it for) while it is running. Therefore, it sounds like something is not working right inside that mechanism. What you should probably try is adjusting the pressure up and down while the pump is running in case there is something in the pump that might be dislodged. If that doesn't work you might be in for a pump rebuild or a new pump.
Chas
LM GS/3 & LaSpaziale Dream v 1.23 (US 120V)
Mazzer Kony E, Customized Rocky
Hottop P/B

bgour
Cappuccino
Posts: 28
Joined: Sat Jan 24, 2009 2:56 am
Location: Vancouver, British Columbia

Re: Brew Pressure Sometimes Gets Very High

Post by bgour » Mon Feb 04, 2019 5:25 pm

Thanks, Chas. I adjusted the expansion valve and took the opportunity to clean it out. Not bad but a bit of crud in there coating everything.

After adjusting the expansion valve to 12.5 bar I retested and found that I was getting the same runaway pressure behaviour but now the max pressure was about 175 psi. At this point the expansion valve was just starting to kick in but that seems to be enough to halt the pressure rise.

I rigged up a way to bleed pressure from my portafilter manometer (to simulate pulling a shot) and tested again. It turns out that I only see the runaway pressure rise if there is zero water bleed. As soon as I open the valve and get even a few drops per second I no longer get the pressure rise. Shrug - perhaps the pump needs a little flow for the pressure mechanism to work correctly. Either way, I don't think this is happening during normal operation.

All good.

Thanks again!
Vivaldi S1 V1, timer
Mazzer Mini

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