Brew pressure issue on a QM67

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
User avatar
GC7
Supporter ♡

#1: Post by GC7 »

After almost 3 years of flawless performance, my Quickmill 67 EVO had a brew pressure problem this morning.

Under the resistance of coffee or the blind back flush basket, the pressure would not go above 4 bar.

The pump is functioning properly. I open the flow control and get about 8.2 ml per second. Moving the expansion valve screw to higher pressure does not alter anything. It had been set to 9 bar and worked the day before. I do see the water flowing to the drip tray when using the backflush basket..

I was advised to change the pump vibratory air release valve and the pump pulsor. I ordered them from Chris Coffee whose service people are great.

Does anyone have any ideas if this can restore brew pressure and fix my problem? If not, what could the problem be?

Thanks

JRising

#2: Post by JRising »

So where is the water going?
Can you see it flowing over the priming valve (air release valve) while the gauge shows 4 bar? I find it very hard to believe that that tiny little valve could pass the full flow of a properly functioning pump at 4 bar. No water is going anywhere else? Nothing over the OPV? Nothing from the E61 Drain?

How's it brewing? Does it seem okay like maybe the gauge sticking at 4 Bar while the machine is working just fine?

User avatar
GC7 (original poster)
Supporter ♡

#3: Post by GC7 (original poster) » replying to JRising »

Water seems to be diverted to the drip tray while the pump is under the resistance of coffee or the back flush disk. The coffee yesterday (one shot only) was a nice long preinfusion then up to 4 bar :D finish. Colombia Anaerobic Red Honey Pink Bourbon. Very tasty.

Thanks for the reply and any help. My order from Chris Coffee for the parts and extra general maintenance items is on the way.

JRising

#4: Post by JRising »

With the top off of the machine you can pinch the silicone hoses to see which one is flowing. Don't pinch too long or the pressure will build up enough to blow the hose off of the OPV.

Watch the gauge while you pinch and release the OPV hose. If your pinch is affecting the pressure by even 1/8 of a bar, then you know the OPV is letting flow at 4 bar (or whatever the gauge says).

User avatar
GC7 (original poster)
Supporter ♡

#5: Post by GC7 (original poster) » replying to JRising »

Thanks. The hose at the bottom of what I'm guessing is the 3 way valve when pinched makes the pressure rise to ~5.5 bar. Additionally, holding it a bit forces water out the steam wand (the boiler is filled from a separate probe issue). Other hoses are unaffected when pinched.

JRising

#6: Post by JRising » replying to GC7 »

Oh. Can you describe where this valve is located?

If water is forced into your boiler when brewing, thus displacing water out from a steam wand, then your boiler fill solenoid is leaking internally allowing the high brew circuit pressure (potentially 9 bar) to escape into the low pressure boiler circuit (potentially 1.3 Bar)...
That would be coming out over your safety OPV or vacuum breaker on the boiler, perhaps? (If the steam valve is closed and it can't escape that way)

User avatar
GC7 (original poster)
Supporter ♡

#7: Post by GC7 (original poster) » replying to JRising »

Thanks,
The bottom hose on that brass3-way piece coming out of the brew boiler is what causes the pressure increase if pinched. It swings around to the top of that same piece via a T-hose connector where the other hose I think goes to the E61 brew outlet.The 3rd hoe out of there goes to the drip dray as far as I can tell.


JRising

#8: Post by JRising »

Okay, that's a combination valve. The thick side is the safety valve. It should always be closed unless your boiler pressure exceeds 1.6 Bar, then it opens to let the pressure out and prevent the boiler from rupturing. If the water is coming out the thick side while the boiler gauge is less than 1.5, then replace this whole valve. It is not a good idea to rebuild a safety valve, if it ends up at a higher release pressure or jammed it is nolonger keeping anything safe.

The skinny side is the vacuum Breaker valve. You may be able to rebuild this if it is constantly leaking. You'll find that it seals by the rush of escaping steam and air raising a teflon disk against a spring until the teflon disk touches an o-ring.
If you disassemble it to clean it, work over a towel and work carefully the spring will make an effort to fly across the room and roll away to another dimension. Once reassembled, test it on the machine. It should slam shut when the boiler passes boiling point, if it hisses and leaks steam replace the whole combination valve.

You're in NY... Chris Coffee has them if you need them:
https://www.chriscoffee.com/products/qm ... -opv-combo

Of course, if it's working properly and the Safety is just letting off pressure because the brew-circuit is leaking into the boiler, you'll need to stop that leak first. It is most likely an internal leak over the boiler fill solenoid. Then see if the Safety valve is okay at normal boiler pressures.

User avatar
GC7 (original poster)
Supporter ♡

#9: Post by GC7 (original poster) »

Thank you again

Nothing ever comes out of the thick side of the valve. All that happen under pressure (4 bar) is water diverting to the drip tray. Pinch off the bottom hose and you stop the drip tray but force liquid out of the steam arm (when shut!)

No water leaks anywhere I can see.

JRising

#10: Post by JRising »

Wait, your steam valve (For the steam wand) is leaking 100% of the time? That would be a reason your boiler isn't building enough pressure to close the vacuum breaker...

From all of the above posts, it seems obvious that you have several issues and will need to tackle each of them in turn...
The boiler is obviously overfilled, but you may need to fix the steam valve leak first, to have control over it, but also leave it opening while tracking down the boiler-overfill issue. Almost certainly your brew circuit is leaking to boiler causing the overfill, clean/inspect the boiler-fill valve. Replace if it leaks after cleaning.
Once you think boiler-fill solenoid valve is repaired, empty boiler and allow the machine to refill it. If it stops at a reasonable level, let it heat and see if vacuum breaker is working as normal or still constantly hissing.
What you find after the first couple steps will determine the next.