webhead Senior Member Joined: 23 May 2003 Posts: 8 Location: Belgium Expertise: I live coffee
Espresso: Promac Green Pu Grinder: Santos
Posted Sun May 11, 2008, 1:43am Subject: Pressure remains too high: cause ?
Hi all,
I recently bought a Promac (commercial) machine and I fixed some issues with the autofill etc.
However, whenever I pour a shot the pressure on the gauge jumps to maximum.
It goes like this: Bush the button, pump activates, pressure rises up to about 8 bar all is fine (this takes about 1-2 seconds) The sound changes and the pressure jumps rapidly to about 16bar (max) on the scale, at this point extraction starts. I can get a decent shot out of it, not too light, not too sour and bitter. The same things happen when I use a blind filter. When I use an empty portafilter the pressure builds up to about 7 bar and holds.
I tried screwing the regulator screw in and out in every direction but I don't see any difference. The gauge does indicate a correct line pressure of 4 bar.
I checked the OPV (which reads "12 BAR") and water does flow from it...
Suggestions ?
Just a note : I'm not yet ready to go and buy additional regulators for line pressure etc as long as I haven't extended all tweaking options on my current setup.
webhead Senior Member Joined: 23 May 2003 Posts: 8 Location: Belgium Expertise: I live coffee
Espresso: Promac Green Pu Grinder: Santos
Posted Sun May 11, 2008, 1:56am Subject: Re: Pressure remains too high: cause ?
oh yeah,
I checked my drip box: the OPV output keeps a constant dripping when on line pressure.... I assume this isn't normal.
I have to add that the machine probably didn't see a lot of operation but someone stored with a filled boiler for 6 years on a shelf. I fixed some issues but some still persist.
DavecUK Senior Member Joined: 21 Sep 2005 Posts: 99 Location: UK Expertise: I love coffee
Espresso: Izzo Alex, Fracino Heavenly,... Grinder: Mazzer Mini E Roaster: Toper 1kg (sold) Gene Cafe
Posted Sun May 11, 2008, 7:21am Subject: Re: Pressure remains too high: cause ?
I'll assume it's a rotary pump, if not ignore everything I say.
It's most likely the bypass on the pump, try removing the whole bypass assembly and cleaning in descaler, if that doesn't work buy a new pump.
The OPV is simply doing it's job and they are set to vent at 12 bar, so with a seized bypass, it will vent all the time. Again the fact that it also does it under line pressure would seem to indicate that it's also probably scaled up. Again disassemble and clean in descaler, if that doesn't fix it buy a new OPV.
While your at it check the anti backflow valve (should be after the rotary pump and before the Boiler/HX), again clean in decscaler, replace if it looks bad.
webhead Senior Member Joined: 23 May 2003 Posts: 8 Location: Belgium Expertise: I live coffee
Espresso: Promac Green Pu Grinder: Santos
Posted Sun May 11, 2008, 12:17pm Subject: Re: Pressure remains too high: cause ?
You're probably right.
I removed the OPV, opened it up and you're absolutely right, it's badly scaled up. I aggressively descaled it and it seems to be in perfect order now.
The fact that turning the pump regulation screw in either direction doesn't do anything does kind off hint towards bypass. However, it's a fluid-o-tech small brass pump so asaic there isn't much to be disassembled. I'm not quite sure how I should descale that one.
Also, I'm not seeing an anti-backflow valve ? Water enters a splitter going to OPV, Hx and a manual/electric fill valve for the boiler. No antibackflow here...
DavecUK Senior Member Joined: 21 Sep 2005 Posts: 99 Location: UK Expertise: I love coffee
Espresso: Izzo Alex, Fracino Heavenly,... Grinder: Mazzer Mini E Roaster: Toper 1kg (sold) Gene Cafe
Posted Sun May 11, 2008, 1:19pm Subject: Re: Pressure remains too high: cause ?
The fact that turning the pump regulation screw in either direction doesn't do anything does kind off hint towards bypass. However, it's a fluid-o-tech small brass pump so asaic there isn't much to be disassembled. I'm not quite sure how I should descale that one.
That's good then, just unscrew the bypass assembly and dump it in descaler, later you can run some through the pump as well (after putting the bypass back again) pump would probably appreciate the descaler running through it if it's been used in hard water, it will also descale the whole brew circuit including the group. I suspect your pump is quite saveable.
Also, I'm not seeing an anti-backflow valve ? Water enters a splitter going to OPV, Hx and a manual/electric fill valve for the boiler. No antibackflow here...
Well sometimes they are not obvious a chunky fitting about 2 inches ling with two nuts on it could be the valve. Of course some manufacturers simply don't go to the bother of fitting them...which is a fairly poor show in my opinion. Their rationale will be that the line pressure from the mains connection will prevent any problems...this however, is only true if the line pressure is above about 1.5 or 1.6 bar (whatever pressure the brew boiler is set to in effect), or they figure your mains water supply to the machine will have a 1 way valve fitted (which is good practice to be honest). This also would mean that running off an unpressurised supply would not work in those machines (e.g. drawing from a container), unless a 1 way valve is fitted to the inlet tube...really though the best place for the valve is after the pump!
The Vane pumps have no way of controlling backflow like a vibe pump, the chamber effectively passes liquid in both directions quite easily when it's not moving and on the FOT pumps, when no rotating no centrifugal force to throw the vanes out.
But hey some manufacturers might like to save a few bucks by not fitting one...
P.S. Sort of like their assumption that the machine will run on water that will never scale the machine....so why would you want a drain fitting on the bottom of the boiler...or liberal use of thread-lock instead of PTFE tape, because...hey it's easier and they don't have to remove those fittings maybe 5-10 years later and worry about the brittle metal snapping..<sigh>
webhead Senior Member Joined: 23 May 2003 Posts: 8 Location: Belgium Expertise: I live coffee
Espresso: Promac Green Pu Grinder: Santos
Posted Sun May 11, 2008, 2:19pm Subject: Re: Pressure remains too high: cause ?
My die hard motivation actually made me disassemble the valve, dump it in hot descaler, clean it up and reassemble it in the time between my posts. I actually found a little stem to be stuck pushing the valve in the "closed" function all the time. Loosening up the screw didn't make it come back up so that did not increase the bypass. Al least from what I think I saw. I cleaned and reassembled it and it seems to move just fine now. Let's hope it's back in busyness.
I have a portafilter and a manometer lying around so I'll be tweaking that shot tomorrow.
You're absolutely right about the construction habits these days. The problem is that this doesn't only happen with cheap equipment but also on well known pricey stuff where the company's new management decided to make an extra buck.
I already descaled/flushed my boiler and groupheads and I fitted a small container in line with the waterinlet so I can dump descaler in it and suck it right back in when I engage my machine. I did wonder why there was no boiler drain... looks like one extra nut wouldn't harm the boiler. Maybe a drip box below that nut... plenty of place left... I'm not about the go that far for my tweaking/modding but it couldn't have hurt them to provide such an option...
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