Post By MrJack
Post By MrJack
Gaggia Classic - Poor brew pressure
My classic is not giving me very good brew pressure. I've removed the shower screen and shower screen holder so there should be almost no restriction. I've done a quick test and get 150mL/min...
Steam is fine, and I can get a good strong stream of water out of the wand too.
I've done a full strip down of the machine so far, including:
- brand new boiler, the old one was severely scaled and missing a lot of aluminium inside
- Descaled, scrubbed and flushed group head
- Pulled apart 3-way solenoid valve and descaled, flushed thoroughly
- Pulled apart OPV, descaled and flushed thoroughly
The shower screen and holder have been replaced in the last ~6 months, so they aren't the issue.
I've also got a new brew thermostat on the way (last replaced ~2 years ago).
While cleaning the OPV I fully removed the adjustment valve (via the hex nut) and tried to screw it back to the same depth it was in before... I don't have a pressure gauge to re-calibrate. However the brew pressure was poor before fiddling with this.
The only thing left I haven't touched (or broken) is the pump.
I just ordered a new ULKA EX5 in the final hope of fixing the thing! Otherwise I've spent a good $200 on replacement parts and still a broken machine
Anyone with some more experience care to give insight or opinion on the problem?
What do you mean by "the brew pressure is poor"? How do you know if you can't measure it?
You seem to be describing things you have done to ensure there is no restrictions or blockages - which leads me to think what you are seeing is low flow during extraction (but not with the portafilter absent).
Pressure in a pump driven system like this is the result of restriction to flow - increase resistance and you increase the pressure (for the same flowrate). In an espresso machine, the are two possible routes:
- via the OPV
- via the group
The flow from the pump will be split between the two routes, in a ratio proportional to their relative resistances.
The resistance in the path to the group depends mostly on the grind and dose. Whereas the OPV will vary it's resistance to flow, maintaining roughly the same pressure across a range of flowrates (that is, flowrate through the OPV). It is not designed to open unless the pressure reaches it's setpoint).
When there is not enough resistance in the path to the group, all of the flow from the pump could flow to the group, without the pressure ever reaching the setpoint and opening the OPV (this is a grind/dose/distribution problem).
When the setpoint of the OPV is too low, or there is too much resistance in the puck, the relative resistance of the flow path to the group is much higher, so less flow goes via the group.
People often describe this as there not being enough pressure to push water through the puck, but that is not correct IMHO.
(Edit: significant resistance, such as a blockage, elsewhere in the flow path to the group will also have this effect, but you would also see reduced flow even without the portafilter in place in this scenario).
So, if I had to guess - either your OPV is set incorrectly, your pump is damaged, or you are grinding too fine/dosing too much.
Last edited by MrJack; 29th January 2016 at 04:49 PM.
Hmm yes apologies, I mean flow rather than pressure.
To be clear, the poor flow was occurring both before and after my strip down and cleaning of the unit.
In the last few weeks the pump has gotten much quieter. It starts loud and then goes very quiet which is unusual.
I have witnessed some back-flow from the OPV into the reservoir, by putting the overflow tube into a separate container and seeing a slow trickle.
In regards to the OPV, I've never adjusted it. The machine is 10+ years old and until today was on the factory setting.
Hmmm? How can you say you never adjusted the OPV when you posted earlier that you cleaned it up and removed the adjustment valve. That alone is an adjustment and you will need a pressure gauge to set it right. I am guessing that it is either a pump issue or narrowing of the brew water passage on the lower part of the boiler due to lack of detergent back flushing.
To get the order of events clear:
1. Experience poor flow out of group head
2. Did the things outlined in OP (including OPV clean and adjustment)
3. Still experiencing poor flow out of group head
Yeah, so I'm leaning toward pump issue since I've pulled the boiler and group head apart and thoroughly cleaned them.
Originally Posted by JojoS
I've tried back flushing and there's a good spurt/burst of water out of the drain pipe. That part of the system has been pulled apart and cleaned also.
10 year old pump which has had regular use would be nearing it's time for replacement anyway.
There's not much more it could be at this stage it seems. On most of the Classics that I have worked on, it's been the pump or a blockage in the 3-way that cause the most grief.
I experienced exactly the same thing with my Gaggia Classic and did exactly the same maintenance routine that you've done including replacing the pump (although I was able to re-use my boiler). In the end I only fixed the issue by replacing the 3-way and I have a feeling you'll need to do the same.
I would agree. I recently had my gaggia fail with similar symptoms. One give away is that pumping through the steam wand still works fine. The reason why the pump is now quiet is that it only makes noise when building up pressure - sitting at 15 bar doesn't make much noise.
I didn't even need to relpace my 3-way, but just clean it out as per this guide. For me the water flow was only temporarily fixed before another block, hence I cleared it and then immediately did a double descale. I learnt my lesson - while I did do occasional descales on it previously, the few years it spent in the UK with its original owner must have fouled it up badly.
Yeah I think you're right. I've just installed the new pump and no improvement Still sitting at < 150mL/min out of the brew head.
Originally Posted by LeroyC
Yep, steam wand gives strong flow. Measured it at >500mL/min.
Originally Posted by burr
I have stripped apart, descaled and manually cleaned the 3-way. Maybe I didn't clean it enough or the blockage is somewhere I can't get at? I'll investigate re-cleaning and/or replacing and report back!
I think you'll end up buying a new 3-way as apparently small, almost microscopic pieces of scale can get in the part of the valve that you can't see and block it. And no matter what you do you'll never get them out. If you want to have one more go at it make sure you replace all the O-rings and make sure you got it done up nice and tight when you put it back together.
Originally Posted by cyclonite
If you are getting that kind of flow with the PF removed, I can't see how a blockage in the 3 way valve can result in the issues described.
A passing three way valve, on the other hand, would provide an alternate route for water to travel - when there is a lot of resistance in the group then water could preferentially flow through the 3 way valve (preventing the pressure rising).
With no coffee in the PF, there is relatively less resistance in that branch (than through the passing valve) , so water flows that way instead.
If you can check for water coming from the 3 way valve during your shot, it would confirm or discount my hypothesis
You're right, it's not a blocked 3-way per se, rather a small blockage inside the valve that prevents it from working properly. Semantics really, but technically you're right. Still needs to be dealt with in the same way.
Originally Posted by MrJack
The only other thing that can cause this is a 3-way that leaks due to a poor seal. This can happen when the seals are old and perished or if it's not done up tight enough. If this is what's happening there'll be tell tale water marks on the outside of the valve assembly.
Just pulled some shots and can confirm: there is no water coming out of the 3-way valve outlet tube during extraction.
Originally Posted by MrJack
There is still a good spurt of water coming out of the outlet after stopping the extraction.
Similarly, with no PF installed, there is no water coming out of the 3-way while flushing water out of the brew head.
So IIUC the theory is:
A bit of sediment inside the valve could cause the valve (when energised) to not seal properly.
If the valve does not seal properly, there is an alternate path (with probably lower resistance) of flow for the water.
Bingo. But it sounds like that might not be happening.
How certain are you that dose /grind are not the problem?
Possibly a leak from the piping somewhere (or the OPV is set too low)?
Last edited by MrJack; 7th February 2016 at 10:15 AM.
So do you think we can rule out the 3-way?
Dose and grind are pretty good. I have a Super Jolly and can consistently achieve a good espresso with a 2x yield recipe: 20g in 40g out in ~30seconds. Previously it would be about 3-4 seconds until first drop, and give a good looking extraction throughout (using a naked PF).
However with this poor flow it's now about 12 seconds until first drop and then quite a watery extraction.
- double check the OPV overflow tube and see if it's still dripping out water, both during extraction and flushing without a PF.
- Look for any leaks or water internally
OK this is interesting: I turned on the machine from cold and was watching the OPV overflow tube. As it heated up, the water in the tube kept creeping up. When I switched on the brew switch it started a steady drip out of the overflow.
This would suggest the OPV is set (way) too low?
So I've tighted the OPV valve (should be set much higher now) to try to rule out the OPV.
I'm no longer seeing any water creeping out of the OPV overflow tube anymore.
However, bafflingly, the flow hasn't improved and I'm not seeing any leaks or water escaping via the 3-way valve seals or outlet.
I put a blind basket in the PF and the first and second flush attempt didn't work.
On the 3rd go it give a big gush and a few scale particles came out!
Now, the flow out of the brew head is back to normal! I'm sure tightening the OPV valve helped otherwise I wasn't able to get the necessary pressure in the brew chamber to backflush the junk stuck in the 3-way valve.
Last edited by cyclonite; 7th February 2016 at 01:53 PM.
There you go. No matter how much it doesn't make sense it almost always comes back to the 3-way. It sounds like you've cleared it this time. If it happens again it probably means you've got scale in your group head that's making its way back into the 3-way so look out for that. Good luck, hope it's all plain sailing from here.